Treponema Pallidum of Medical Bacteriology

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Treponema Pallidum of Medical Bacteriology

Treponema pallidum is included in the family Spirochaetaceae. They are slender spirochaetes with fine spirals having pointed ends. Some of them are pathogenic for humans, while others are normal flora in mouth and genitalia.

These pathogens are strict parasites and the diseases caused by Treponema are called Treponematoses. Treponema pallidum is the causative agent of syphilis. The name Treponema pallidum is derived from Greek words, which means, Trepos – Turn Nema – Thread and palladium – Pale staining.

Morphology

It is thin, delicate spirochete with tapering ends, about 10µm long and 0.1-0.2 µm wide. It has about ten regular spirals, which are sharp and angular, at regular intervals of about 1µm. They are actively motile (endoflagella), exhibiting rotation around the long axis, backward and forward movements and flexion of the
whole body.

It cannot be seen under light microscope and does not take ordinary bacterial stains. It can be seen under the dark ground (Figure 7.22) or phase contrast microscope.It can be stained by silver impregnation method.
Treponema Pallidum of Medical Bacteriology img 1

Culture

  • Pathogenic Treponema cannot be grown in artificial culture media.

Pathogenesis

Source of infection – Human beings (patients)
Mode of transmission – Sexual contact
Site of entry – Through minute abrasions/cuts on skin or mucosa

Incubation period – 10 – 90 days

  • Treponema pallidum causes venereal syphilis, which is acquired by sexual contact. The pathogen enters the human body through cut on the skin or mucosa of genital areas.
  • The clinical disease sets in after an incubation period of about a month. There are 3 clinical stage of venereal syphilis, namely – primary, secondary and tertiary syphilis.

Primary syphilis

  • A papule appears on the genital area that ulcerates, forming a chancre of primary syphilis called hard chancre.
  • The chancre is covered by thick exudates, very rich in spirochetes.
  • The regional lymph nodes are swollen, discrete, rubbery and non – tender.
  • Even before the chancre appears, the spirochetes spread from the site of entry into the lymph and bloodstream, so the patient may be infectious during the late incubation period.
  • The chancre invariably heals within 10-40 days, even without treatment, leaving a thin scar.

Secondary syphilis

  • Secondary syphilis sets in 1-3 months after the primary lesion heals. During this interval, the patient is asymptomatic.
  • The secondary lesions are due to widespread multiplication of the spirochetes and dissemination through the blood.
  • Secondary syphilis is characterized by appearance of papular skin rashes, mucous patches in the oropharynx and condylomata (a raised growth on the skin resembling a wart).
  • The lesions are abundant in spirochetes and the patient is most infectious during the secondary stage.
  • There may be retinitis (inflammation of the retina of the eye), meningitis, periostitis, and arthritis.
  • Secondary lesions usually undergo spontaneous healing, in some cases taking as long as 4 or 5 years.
  • After the secondary lesions disappear, there is a period of dormant known as latent syphilis the patient does not show any clinical symptoms but with positive serology.

Tertiary syphilis

  • After several years, manifestations of tertiary syphilis appear. These consist of cardiovascular lesions including aneurysms (enlargement of an artery), gummata (a small rubbery granuloma that has a necrotic centre) and meningovascular manifestations. Tertiary lesions contain few spirochetes.
  • In few cases, neurosyphilis such as tabesdorsalis or general paralysis of the insane develops. These are known as late tertiary or quaternary syphilis.

Congenital syphilis

In congenital syphilis, the infection is transmitted from mother to fetus by crossing the placental barrier.

Non – Venereal syphilis

It may occur in doctors or nurses due to contact with patients lesion during examination. The primary chancre occurs usually on the fingers.

Laboratory Diagnosis

The diagnosis of syphilis includes

  1. Demonstration of Treponemes
  2. Serological tests

Specimen:
Exudates are collected from the chancre. Blood (serum) is collected for serology.

Demonstration of Treponemes

a. Dark ground microscopy:

The wet film is prepared with exudates and examined under dark ground microscope. Under dark field examination Treponema pallidum appears motile spiral organism.

b. Treponemes in tissues:

It can be demonstrated by silver impregnation method of staining.

Serological tests

Non – Treponemal tests – In the standard tests for syphilis includes;

  • VDRL – Venereal Diseases Research Laboratory test.
  • RPR – Rapid Plasma Reagain (Figure 7.23).

VDRL or RPR tests are used for serological screening for syphilis and more useful for the assessment of cure following treatment.
Treponema Pallidum of Medical Bacteriology img 2

Treponemal Tests:

The treponemal tests includes

  • TPHA – Treponema pallidum hemagglutination assay
  • FTA – ABS – Fluorescent treponemal antibody absorption test.

These two tests are used to confirm the diagnosis.

Treatment and Preventive Measure

In early syphilis

  1. Benzathine benzyl penicillin, 24 lakhs units intramuscularly in a single dose.
  2. Alternatively, doxycycline 100 mg twice a day orally for 15 days.

In late syphilis

Benzathine benzyl penicillin 24 lakhs units, intramuscularly once weekly for 3 weeks.

  1. Avoiding sexual contact with an infected individual.
  2. Use of sex barriers (condoms).

Mycobacterium Tuberculosis (Tubercle Bacillus)

Learninsta presents the core concepts of Microbiology with high-quality research papers and topical review articles.

Mycobacterium Tuberculosis (Tubercle Bacillus)

The genus Mycobacterium is distinguished by its thick, complex, lipidrich waxy cell walls. This high lipid content (Mycolic acids) imparts the characteristic of acid fastness or resistance to decolorization by a strong acid after staining with carbol fuchsin. Many of the Mycobacterial species are saprophytes but several species are highly significant human pathogens.

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB) It is a killer disease and ranks as one of the most serious infection diseases of the developing countries. TB is primarily a disease of the lungs but may spread to other sites of the body.

The name Mycobacterium tuberculosis is derived form,

  • Mycobacterium (Greek) – Fungus like bacterium
  • Tuberculosis (Latin) – Swelling or Knob

Morphology

They are acid fast bacilli, slightly curved rods, it may occur singly or in small clumps. They are non-motile, non-sporing, and non-capsulated.

Cultural Characteristics

They are obligate aerobe, optimum temperature is 37°C and optimum pH is 6.4-7.0. The pathogen grows on an enriched culture media – Lowenstein Jensen medium.

The colonies appear in about 2-3 weeks. The colonies are dry, rough, raised, irregular colonies with a wrinkled surface. Initially creamy white and becoming yellowish later (Figure 7.19).
Mycobacterium Tuberculosis (Tubercle Bacillus) img 1

Pathogenesis

Human tuberculosis is divisible into two form, they are Primary TB and Secondary TB. The pathogenesis of Primary Tuberculosis is described in flowchart 7.8.

Source of infection – Airborne droplets
Route of entry – Respiratory tract
Incubation period – 3 – 6 weeks.
Mycobacterium Tuberculosis (Tubercle Bacillus) img 2

Secondary TB – (Post primary TB)

It is caused by reactivation of the primary lesion or by exogenous reinfection. Granulomas of secondary TB most often occur in the apex of the lungs. The necrotic element of the reaction causes tissue destruction and the formation of large area of caseation termed tuberculomas.

The presence of caseous necrosis and cavities are two important clinical manifestations of secondary TB. The cavities may rupture into blood vessels, spreading the bacilli throughout the body and break into airways, releasing the pathogen in aerosols and sputum – called as open tuberculosis (Figure 7.20).
Mycobacterium Tuberculosis (Tubercle Bacillus) img 3

Clinical Symptoms

It includes, cough that lasts for more than 2-3 weeks, weight loss, fever, night sweat and loss of appetite.

Laboratory Diagnosis

Specimen:

In case of pulmonary tuberculosis the most usual specimen is sputum.

Direct Microscopy:

Smear is made from the sputum specimen and stained by Ziehl – Neelson technique. It is examined under oil immersion objective lens. The acid fast bacilli appear as bright red bacilli against a blue background.

Culture:

The specimen is inoculated onto LJ – medium and incubated at 37°C for 2 weeks the tubercle bacilli usually grow in 2-8 weeks. The bacterial growth is confirmed by Ziehl – Neelsonstaining.

1. Tuberculin Skin test

Mantoux test:

This method has been used routinely. In this test 0.1 ml of PPD (Purified protein derivative) containing 5 TU (Tuberculin unit) is injected intradermally on the flexor aspect of forearm (Figure 7.21) The site is examined after 48-72 hours and induration are measured (diameter in mm).

Positive test:

Indurations of diameter d10 mm or more is considered positive.

Negative test:

Indurations of 5 mm or less is negative.

2. Gene Xpert MTB

It is an automated diagnosis test it detects DNA sequences specific for M. tuberculosis and rifampicin resistance by PCR. Results can be obtained within 2 hours.

Treatment

The antitubercular drugs include two types of agents which are;

Bactericidal agents – Rifampicin (R), Isoniazid (H), Pyrazinamide (z), Streptomycin.
Bacteriostatic agents – Ethambutol (E).

The regimen for treating TB consists of an intensive phase of 2 months of isoniazid, rifampin, pyrazinamide and ethambutol, followed by a continuation phase of 4 months of isonizid and Rifampin.

Prophylaxis and Control Measures

The BCG (Bacille – Calmette – Guerin) administered by intradermal injection of the live attenuated vaccine. The immunity may last for about 10 years. The prevention of TB can be done by the following general measures such as

  1. Adequate nutrition.
  2. Practicing good hygiene (washing hands)
  3. Health education.
  4. Cover the mouth with a tissue when you cough or sneeze.

The p-Block Elements Class 12 Notes Chemistry Chapter 7

By going through these CBSE Class 12 Chemistry Notes Chapter 7 The p-Block Elements, students can recall all the concepts quickly.

The p-Block Elements Notes Class 12 Chemistry Chapter 7

The p-block elements are placed in groups 13 to 18 of the periodic table. Their valence shell electronic configuration is ns2np6 to ns2np6 (except He which has 1s2 electronic configuration.)

Group 15 Elements: Group 15 elements include Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb) and Bismuth (Bi).

Table 7.1: Atomic and Physical Properties of Group 15 Elements
The p-Block Elements 12 Notes Chemistry 1
αE111 single bond (E = element); bE3-; cE3+; dWhite phosphorus; eGrey α-format 38.6 atm of Sublimation temperature; g At 63 K h Grey α-form; Molecular N2

As we go down the group, there is a shift from non-metallic to the metallic character through metalloids character. N and P are non-metals, AS and Sb are metalloids and Bi is a typical metal.

→ Occurrence: N2 comprises 78% by volume of the atmosphere. In the earth’s crust, it occurs as sodium nitrate (NaNO3) called Chile saltpetre and potassium nitrate (KNO3) called Indian saltpetre. It is found in the form of proteins in plants and animals. Phosphorus (P) occurs in minerals of the apatite family Ca9 (PO4)6. CaX2 [X = F, Cl, or OH] e.g. fluorapatite Ca9 (PO4)6. CaF2 which are the main components of the phosphate rocks. P is an important constituent of animal and plant matter and is present in bones and living cells.

→ Electronic Configuration: The valence shell electronic configuration of these elements is ns2np3. The s orbital is completely filled and p orbitals are exactly half-filled (px1 py1 Pz1). Thus their electronic configuration is extra stable.

→ Atomic and Ionic Radii: Covalent and ionic radii increase in size down the group due to the addition of the orbit each time. There is a considerable increase from N to P. However, from As to Bi only a small increase in covalent radius is observed. This is due to the presence of completely filled d and /or f orbitals in heavier members.

→ Ionization Enthalpy: I.E. values of Group 15 elements is much greater than that of Group 14 elements due to the extra-stability of half-filled p-orbitals and smaller size. It decreases from top to bottom within the group due to a gradual increase in atomic size. The order of successive ionisation enthalpies is ΔiH1 < ΔiH2 < ΔiH3.

→ Electronegativity: Electronegativity decrease down the group. The difference is not much pronounced amongst the heavier elements.

→ Physical Properties: All the elements are polyatomic. Dinitrogen (N2) is a diatomic gas while others like P4 etc. are solids. The b. pts; in general, increase from top to bottom in the group, but them. pts increase up to As and then decrease up to Bi.

Except for Nitrogen, all the elements show allotropy.

Chemical Properties:
Oxidation states and trends in chemical reactivity: Tire common oxidation states of these elements are – 3, + 3 and + 5. The tendency to exhibit – 3 oxidation state decreases down the group due to an increase in size and metallic character.

N does not show + 5 oxidation state due to the absence of d-orbitals and Bi does not show + 5 oxidation state due to the Inert pair Effect. The only well characterised Bi (V) compound is BiF5. N exhibits + 1, + 2, + 4 oxidation states also when it reacts with oxygen. P also exhibits + 1 and + 4 oxidation states in some oxoacids.

In the case of N, all oxidation states from + 1 to + 4 tend to disproportionate into acid solution1. For example
3 HNO2 → HNO3 + 2 NO + H2O

Similarly, in the case of P nearly all intermediate oxidation states disproportionate into + 5 and – 3 both in alkali and acid,

Anomalous properties of Nitrogen: N differs from its congeners due to

  1. its smaller size.
  2. high electronegativity and high ionisation enthalpy.
  3. non-availability of d-orbitals.

Nitrogen has a unique ability to form an-pit multiple bonds with itself and with other elements having small size and having high electronegativity (e.g., C, O)

N2 has a triple bond: N ≡ N [one a and two K bonds]
∴ Its bond enthalpy (941.4 kJ mol-1) is very high.
P and As can form dπ-pπ bonds with transition metals.

1. Reactivity towards hydrogen: All the elements of Group 15 form hydrides of the type EH3 where E = N, P, As, Sb, Bi. The stability of hydrides decreases from NH3 to BiH3 and hence reducing character increases from NH3 to BiH3. Basicity of hydrides also decreases in the order NH3 > PH3 > AsH3 > SbH3 > BiH3.

Table 7.2: Properties of Hydrides of Group 15 Elements
The p-Block Elements 12 Notes Chemistry 2
2. Reactivity towards oxygen: All these elements form oxides: E2O3 and E2O5. The oxide in the higher oxidation state is more acidic.
Their acidic character decreases down in a group. The oxides of the type EO3 of N and Pare purely acidic, that of As, Sb amphoteric and those of Bi predominantly basic.

3. Reactivity towards halogens:
2E + 3X2 → EX3
2E + 5X2 → 2EX5
N does not form pentahalide due to absence of d-orbitais. All trihalides are stable except that of N.

Pentahalides are more covalent than trihalides.

4. Reactivity towards metals: These elements combine with metals showing – 3 oxidation state in compounds like Ca3N2, Ca3P2, Mg3Bi2.

Dinitrogen, N2:
Preparation:
1. Commercially dinitrogen is produced by the liquefaction and fractional distillation of air when N2 distils the first.

2. Lab. Method:
NH4Cl (aq) + NaNO2 (aq) → N2 (g) + 2H2O (l) + NaCl (aq)

The p-Block Elements 12 Notes Chemistry 3

3. Pure N2 can be obtained from sodium or barium azide.
The p-Block Elements 12 Notes Chemistry 4

→ Properties: Dinitrogen is a colourless, odourless, tasteless and non-toxic gas. It has two stable isotopes: 14N, 15N. It has very low solubility in water.

Because of the high bond enthalpy of N ≡ N, dinitrogen is rather inert at room temperature.

At high temperature, it directly combines with some metals to form largely ionic nitrides and with non-metals, covalent nitrides.
The p-Block Elements 12 Notes Chemistry 5
Haber’s process:
The p-Block Elements 12 Notes Chemistry 6

Uses:

  1. Manufacture of NH3 and Calcium Cyanamide.
  2. To create an inert atmosphere.
  3. Liquid N2 is used as a refrigerant,

Ammonia:
Preparation:
1. From Urea:
NH2CONH2 + 2H2O → (NH4)2 CO3 → 2NH3 + H2O + CO2

2. From ammonium salts and caustic soda/lime.
2NH4Cl + Ca(OH)2 → 2NH3 + 2H2O + CaCl2
(NH4)2 SO4 + 2 NaOH → 2NH3 + 2H2O + Na2SO4

3. On a large scale, it is prepared by Haber’s process.
The p-Block Elements 12 Notes Chemistry 7

The pressure is 200 × 105 Pa and iron oxide with small amounts of K2O and Al2O3 is used as a catalyst,

Properties of Ammonia:

  1. It is a colourless gas with a pungent smell.
  2. It shows hydrogen bonding in solid and liquid states.

Structure of NH3:
The p-Block Elements 12 Notes Chemistry 8

3. It is highly soluble in water. Its aqueous solution is weakly basic.
NH3 (g) + H2O (l) ⇌ NH4+ (aq) + OH– (aq)

4. It forms ammonium salts with acids.
NH3 + HCl → NH4Cl

5. As a weak base it precipitates the hydroxides of many metals
from their salt solutions, e.g.,
The p-Block Elements 12 Notes Chemistry 9
6. Due to its tendency to donate a pair of electrons on N, it acts as a Lewis-Base, forms complexes with Cu2+, Ag+.
The p-Block Elements 12 Notes Chemistry 10
The p-Block Elements 12 Notes Chemistry 11
Uses:

  1. Production of nitrogenous fertilizers.
  2. Production of nitric acid.
  3. Liquid ammonia is a non-aqueous solvent.
  4. Liquid NH3 is a referigerant.

Oxides of Nitrogen: Nitrogen forms a number of oxides in different oxidation state. The details of names, formulae, ox. state, preparation, colour etc. are given:
The p-Block Elements 12 Notes Chemistry 12
Lewis dot main resonance structures and bond parameters of oxides are given on the next page.

Table 7.4 Structures of Oxides of Nitrogen
The p-Block Elements 12 Notes Chemistry 13
Nitric Acid, HNO3
Preparation: It is prepared in the laboratory by heating NaNO3 or KNO3 and cone. H2SO4.
The p-Block Elements 12 Notes Chemistry 14
Method of manufacture of Nitric acid by Ostwald’s process.

Step:
1. Catalytical oxidation of NH3 by O, or air.
The p-Block Elements 12 Notes Chemistry 15
2. NO thus formed combines with 02 giving NO2
2NO (g) + O2 (g) ⇌ 2NO2(g).

3. N02 SO formed dissolves in water to give HNO3.
3NO2 + H2O(l) → 2 HNO3 + NO (g)

Structure of HNO3: In the gaseous state, HNO3 exists as a planar molecule.
The p-Block Elements 12 Notes Chemistry 16
In an aqueous solution, it behaves as a strong acid.
HNO3 (aq) + H2O (Z) → (aq) + NO3 (aq).
Concentrated HNO3 is a strong oxidizing agent.

→ Reaction with Cu:
3Cu + 8 HNO3 (dil) → 3 Cu (NO3)2 + 2 NO + 4 H2O
Cu + 4 HNO3 (cone.) → Cu (NO3)2 + 2NO2 + 2H2O

→ Reaction With Zinc
4 Zn + 10 HNO3 (dil.) → 4 Zn (NO3)2 + 5 H2O + N2O
Zn + 4HNO3 (cone.) → Zn (NO3)2 + 2H2O + 2NO2

→ Reaction with I2
The p-Block Elements 12 Notes Chemistry 17
→ Reaction with Carbon
C + 4 HNO3 → CO2 + 2H2O + 4NO2

→ Reaction with Sulphur
S8 + 48 HNO3 (Cone.) → 8H2SO4 + 48 NO2 + 12 H2O

→ Reaction with Phosphorus
P4 + 20 HNO3 → 4H3PO4 + 20 NO2 + 4H2O

→ Brown Ring Test for nitrates (NO3–)
NO3– + 3 Fe2+ + 4 H+ → NO + 3 Fe3+ + 2H2O.
The p-Block Elements 12 Notes Chemistry 18
Uses of Nitric acid:

  1. Oxidant in the laboratory.
  2. manufacture of ammonium nitrate for fertilizers.
  3. manufacture of explosive like TNT, nitroglycerine. Phosphorus: Phosphorus exists in three important allotropic forms: white, red and black.

White Phosphorus: White Phosphorus consists of discrete tetrahedral molecules as shown:
The p-Block Elements 12 Notes Chemistry 19
White phosphorus P4

Red Phosphorus: Red Phosphorus is obtained by heating white phosphorus at 573 K in an inert atmosphere for several days. It is much less reactive than white phosphorus. It is polymeric, consisting of P4 tetrahedral linked together as shown in Fig. below.
The p-Block Elements 12 Notes Chemistry 20
Red Phosphorus

Black Phosphorus has two forms α-black phosphorus and β-black phosphorus. α-Black phosphorus is formed when red phosphorus is heated in a sealed tube at 803 K. It can be sublimed in air and has opaque monoclinic or rhombohedral crystals. It does not oxidise in the air. β-Black phosphorus is prepared by heating white phosphorus at 473 K under high pressure. It does not bum in the air up to 673 K.

Phosphine (PH3) Preparation:
1. From calcium phosphide and H2O/dil. HCl
Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3.
Ca3P2 + 6HCl → 3CaCl2 + 2PH3.

2. Lab. Method: By heating white phosphorus with cone. NaOH in an inert atom of CO2.
P4 + 3NaOH +- 3H2O → PH3 + NaH2PO2 (Sod. hypophosphite)

Properties:

  1. Colourless gas with rotten fish smell, highly poisonous.
  2. Explodes in contact with traces of oxidizing agents like HNO3 Cl2 etc.,
  3. Slightly soluble in water.
  4. When absorbed in CuSO4 or HgCl2 solutions, phosphides are obtained.
    3 CuSO4 + 2 PH3 → Cu3P2 + 3H2SO4
    3HgCl2 + 2PH2  → Hg2 P2 + 6HCl.
  5. PH3 is weakly basic like NH3.
    PH3 + HBr → PH4Br.

Phosphorus halides: P forms two types of halides, PX3 [X = F, Cl, Br, I]and PX5[X = F,Cl,Br]
Phosphorus trichloride (PCl3)

Preparation:
P4 + 6Cl2 → 4PCl3.

Properties:

  1. Colourless oily liquid.
  2. Hydrolysis in the presence of mixture.
    PCl3 + 3H2O → H3PO3 + 3HCl

Shape: It has a pyramidal shape as shown in which phosphorus is sp3 hybridized.
The p-Block Elements 12 Notes Chemistry 21
Shape of PCl3

Phosphorus pentachloride (PCl5)
Preparation:
The p-Block Elements 12 Notes Chemistry 22

Properties:

  1. It is a yellowish-white powder.
  2. In moist air, it hydrolyses first to PoCl3, and then H3PO4.
    PCl5 + H2O → POCl3 + 2 HCl
    POCl3 + 3H2O → 4 H3PO4 + 3HCl
  3. On heating, it sublimes but decomposes on stronger heating.
    The p-Block Elements 12 Notes Chemistry 23

In gaseous and liquid phases, it has a trigonal bipyramidal structure shown below. The three equatorial P-Cl bonds are equivalent, while the two axial bonds are longer than equatorial bonds. This is due to the fact that the axial bond pairs suffer more repulsion as compared to equatorial bond pairs.
The p-Block Elements 12 Notes Chemistry 24
In the solid-state, it exits as an ionic solid, [PCl4]+[PCl6]– in which the cation, [PCl4]+ is tetrahedral and the anion, [PCl6]+ octahedral.

Oxo-Acids of Phosphorus: P forms a number of oxo-acids like

  1. Hypophosphorous acid (H3PO2) (ox. state + 1)
  2. Orthophosphoric acid (H3PO3) (ox. state + 3)
  3. Pyrophosphrus acid (H4P2O5) (ox. state + 3)
  4. Hypophosphoric acid (H4P2O6) (ox. state +4)
  5. Orthophosph’oric acid (H3PO4) (ox. state + 5)
  6. Pyrophosphoric acid (H4P2O7) (ox. state +5)
  7. Metaphosphoric acid (HPO3) (ox. state + 5)

The compositions of the oxo-acids are interrelated in terms of loss or gain of H2O molecule or oxygen atom.
These acids in the + 3 oxidation state of P tend to disproportionate as follows:
The p-Block Elements 12 Notes Chemistry 25
The acids which contain the P-H bond are strong reducing agents.
The p-Block Elements 12 Notes Chemistry 26
Group 16 Elements: Oxygen (O), Sulphur (S), Selenium (Se), Tellurium (Te) and Polonium (Po) constitute Group 16 of the periodic table. They are also called Chalcogens (ore-forming).

→ Occurrence: Oxygen is the most abundant of all the elements of the earth. Dry air contains 20.95% oxygen by volume. However Sulphur is present in the earth’s crust to 0.03 – 0.1% only. Combined Sulphur is present in gypsum CaSO4. 2H2O, Epsom salt MgSO4.7H2O. Selenium and tellurium are also found as metal selenides and tellurides in sulphide ores.

→ Electronic Configuration: The elements of Group 16 have six electrons in the outermost shell and have ns2np4 general electronic configuration.

→ Atomic and Ionic Radii: Due to the increase in the no. of shells, atomic and ionic radii increase from top to bottom, The size of the oxygen atom is, however, exceptionally small.

→ Ionisation Enthalpy: Ionisation enthalpy decreases down the group.

Table: Some Physical Properties of Group 16 Elements
The p-Block Elements 12 Notes Chemistry 27
aSingle bond; bApproximate value; cAt the melting point; dRhombic sulphur; eHexagonal grey; fMonoclinic form, 673 K.
Oxygen shows oxidation states of + 2 and +1 in oxygen fluorides OF2 and O2F2 respectively.

→ Electron Gain Enthalpy: Because of the compact nature of the oxygen atom, it has less negative electron gain enthalpy than sulphur.

→ Electronegativity: Next to F, oxygen has the maximum value of electronegativity value amongst the elements. Within the group, its value decreases from top to bottom implying that metallic character increases from O to Po.

→ Physical Properties: Oxygen and Sulphur are non-metals, Selenium and Tellurium metalloids, whereas Polonium is a metal. Pollonium is radioactive [t1/2 = 13.8 days]

All these elements exhibit allotropy.
M.Pts and B.Pts. increase with the increase in atomic no. down the group. The large difference between the M.Pts and B.Pts. of oxygen and sulphur may be explained on the basis of their atomicity: Oxygen exists as diatomic molecules (O2) whereas Sulphur exists as polyatomic (S8).

Chemical Properties:
Oxidation states and trends in chemical reactivity:
O = – 2, -1, +1, (in O2F2), + 2 (in OF2)
S = – 2, + 2, +4, + 6 (in SF6)
Se = – 2, (+ 2), +4, + 6 (SeF6)
Te=-2,(+2), +4, + 6(TeF6)
Po = + 2, + 4
[Within brackets less stable.]

The stability of + 4 oxidation state increases and that of + 6 decreases due to the Inert-pair Effect. Bonding in + 4, + 6 oxidation states are primarily covalent.

The anomalous behaviour of oxygen is due to its

  1. small size,
  2. high electronegativity,
  3. absence of d-orbitals.

1. Reactivity with Hydrogen.
(a) There is strong hydrogen bonding in H2O which is not found in H2S.
(b) All the elements of Group 16 form hydrides of the type H2E[E = S, Se, Te, Po]
(c) H2O is neutral. Other hydrides are acidic and acidic character increases.
H2O < H2S < H2Se < H2Te < H2Po
(d) Thermal stability decreases:
H2O > H2S > H2Se > H2Te > H2Po
(e) H2O does do not have reducing character. Reducing character increases from H2S < H2Se < H2Te.

2. Reactivity with Oxygen: All these elements form oxides of EO2 and EO3 types [E = S, Se, Te, or Po]. Both types are acidic in nature.

3. Reactivity towards halogens: Elements of Group 16 form a large no. of halides of the type, EX6, EX4, EX2 where X = halogen. The stability of the halides decreases in the order F– > Cl > Br > I–

Dioxygen, O2:
The p-Block Elements 12 Notes Chemistry 28
Industrially, O2 is obtained from air by first removing CO2 and water vapour and then, the remaining gases are liquified and fractionally distilled to give N2 and O2.

Properties of O2:

  1. Colourless, odourless gas.
  2. 30.8 cm33 of O2 soluble per litre of water at 293 K.
  3. It has three isotopes 16O, 17O, 18O.
  4. Molecular oxygen (O2) is paramagnetic.
  5. Reactions with metals, non-metals and other compounds are as follows:
    The p-Block Elements 12 Notes Chemistry 29
    The p-Block Elements 12 Notes Chemistry 30

Uses:

  • It is used in oxyacetylene welding.
  • Manufacture of many metals, particularly steel.
  • Oxygen cylinders are widely used in hospitals, high altitude flying and mountaineering.
  • The contraction of fuels, e.g., hydrazines in liquid oxygen, provides tremendous thrust in rockets.

→ Simple Oxides: A binary compound of oxygen with another element is called oxide.

Oxides can be simple like MgO, Al2O3 or mixed like Pb3O4, Pe3O4.
In general metallic oxides like CaO, BaO, Na2O are basic. Non-metal oxides like SO2, CO2 are acidic.

Some oxides like Al2O3 are amphoteric. They react with acids as well as bases.
Al2O3 + 6 HCl → 2AlCl3 + 3H2O.
Al2O3 + 2NaOH → 2Na AlO2 + H2O

Ozone, O3: Ozone is an allotropic form of oxygen. At a height of 20 km from sear level, it is formed from atmospheric oxygen in the presence of sunlight.
The p-Block Elements 12 Notes Chemistry 31
The ozone layer protects the earth’s surface from UV rays.

Preparation:
The p-Block Elements 12 Notes Chemistry 32
ΔH° = + 142 kJ mol-1

Properties:

  1. It is a pale blue gas, dark blue liquid and violet-black solid.
  2. O3 is thermodynamically unstable w.r.t. O2.
    ∴ It acts as a powerful oxidizing agent.

O3 → O2 + O
1.  It oxidizes lead sulphide to lead sulphate.
PbS + 4O3(g) → PbSO4 (s) + 4O2

2. It oxidizes I– ions to iodine
2I– (aq) + H2O (l) + O3 (g) → 2 OH– (aq) + I2 (s) + O2 (g)

3. It oxidizes NO to NO2
NO (g) + O3 (g) → NO2 (g) + O2 (g)

Structure: The two oxygen-oxygen bond lengths in the ozone molecule are identical (128 pm) and the molecule is angular as expected with a bond angle of about 117°. It is a resonance hybrid of two main forms:
The p-Block Elements 12 Notes Chemistry 33
Uses:

  1. It is used as a germicide, disinfectant and for sterilising water.
  2. It is also used for bleaching oils, ivory, flour, starch.
  3. It is an oxidizing agent.

Sulphur-Allotropic Forms: Out of numerous allotropes, the two most important forms are:

  • Yellow rhombic (α-sulphur),
  • Monoclinic (β-Sulphur)
    The p-Block Elements 12 Notes Chemistry 34

The temperature 369 K is called Transition temperature.
The p-Block Elements 12 Notes Chemistry 35
The structure of (a) S8 ring in rhombic sulphur and (b) S6 form:
The p-Block Elements 12 Notes Chemistry 36
Both rhombic and monoClinic Sulphur have S8 molecules. These S8 molecules are packed to give different crystal structures. The S8 ring in both forms is puckered and has a crown shape.

In cyclo-S6 the ring adopts the chair form. At elevated temperatures (~ 1000 K) S2 is the dominant species and is paramagnetic like O2

Sulphur Dioxide (SO2):
Preparation:
1. By burning S in air or O2.
S(s) + O2(g) → SO2(g)

2. Lab. Method: By treating a sulphite with dilute H2SO44.
SO32- (aq) + 2H+ (aq) → H2O (l) + SO2(g)

3. Industrially, it is produced by roasting of sulphide ores:
The p-Block Elements 12 Notes Chemistry 37
Properties:
1. It is a colourless gas with a pungent smell.

2. It is highly soluble in water.

3. It liquefies at room temp, under a pressure of 2 atmospheres.

4. Liquified SO2 boils at 263 K.

5, SO2 when dissolved in water, forms sulphurous acid.
SO2(g) + H2O (l) → H2SO3 (aq)

6. Reaction with NaOH:
The p-Block Elements 12 Notes Chemistry 38
The p-Block Elements 12 Notes Chemistry 39
7. Reaction with Cl2:
The p-Block Elements 12 Notes Chemistry 40
8. Reaction with O2:
The p-Block Elements 12 Notes Chemistry 41
9. Moist SO2 behaves as a reducing agent. It reduces iron (III) ions to iron (II) ions and decolourised acidified potassium permanganate(VII) solution. It is a test for SO2 gas.
2Fe3+ (aq) +SO2 + 2H2O → 2 Fe2+ (aq) + SO42- + 4H+
5 SO2 + 2 MnO4– + 2H2O → 5 SO4 2- + 4H+ + 2 Mn2+

Structure: The molecule of SO2 is angular. It is a resonance hybrid of the two canonical structures
The p-Block Elements 12 Notes Chemistry 42
Uses:

  • Refining of petroleum, sugar
  • Bleaching wool and silk.
  • Antichlor, disinfectant and preservative.
  • Manufacture of H2S04 and other industrial chemicals.
  • Liquid S02 is used as a solvent.

Oxo-Acids of Sulphur: Sulphur forms a number of oxo-acids such as H2SO2, H2S2O3, H2S2O4, H2S2O5, H2SxO6 (X = 2 to 5), H2SO4, H2S2O7, H2SO5, H2S2O8.
The p-Block Elements 12 Notes Chemistry 43
Structures of Sulpiwrous and Sulphuric acids

Sulphuric Acid (H2SO4): It is called the king of chemicals and is one of the most widely used industrial chemicals.

→ Manufacture: Sulphuric acid is manufactured by Contact Process which involves 3 steps:

  1. Burning of Sulphur or Sulphide ores in the air to produce SO2.
  2. Conversion of SO2 into SO3 by reaction with air in the presence of catalyst V2O5.
  3. Absorption of SO3, in H2SO4, to give Oleum (H2S2O7).
    The key step is the catalytical oxidation of SO2 with O2 to give SO3 in the presence of V2O5.
    The p-Block Elements 12 Notes Chemistry 44
    The reaction is exothermic, reversible and proceeds with a decrease in volume.
    ∴ Low temperature (720 K) and high pressure (2 bar) are favourable conditions for maximum yield.

The tempi should not be very low otherwise the rate of reaction will below.

The SO3 gas from the catalytical converter is absorbed in concentrated H2SO4 to produced Oleum (H2S2O7) which on dilution with water gives H2SO4 of the desired concentration.
SO3 + H2SO4 → H2S2O7 (oleum)
H2S2O7 + H2O → 2 H2SO4

The sulphuric acid obtained by the contact process is 96-98% pure.
The p-Block Elements 12 Notes Chemistry 45
Flow diagram the iiai1ufat true of sulphuric acid

Properties:

  1. H2SO4 is a colourless, dense, oily liquid.
  2. It dissolves in water producing a large amount of heat. Hence it should be slowly added to water (and never water in acid)

The chemical properties of H2SO4 are due to its
(a) low volatility,
(b) strong acidic character,
(c) strong affinity for water,
(d) ability to act as an oxidizing agent.

In water, it ionises in 2 steps:
1. H2SO4 (aq) + H2O (l) → H3O+ (aq) + HSO4– (aq)
Ka1 = very large (> 10)

2. HSO4–(aq) + H2O (l) → H3O+ (aq) + SO4 2- (aq);
Ka2 = 1.2 × 10-2.

(a) It is used to prepare more volatile acids:
NaNO3 + H2SO4 → NaHSO4 + HNO3.
2 NaCl + H2SO4 → Na2SO4 + 2 HCl

(b) Cone. H2SO4 is a strong dehydrating agent
The p-Block Elements 12 Notes Chemistry 46
(c) Hot cone. H2SO4 is a strong oxidising agent
H2SO4 → H2O + SO2 + O

(d) Reaction with metals and non-metals:
Cu + 2 H2SO4 → CuSO4 + SO2 + 2H2O
C + 2H2SO4 (cone.) → CO2 + 2SO2 + 2H2O

Uses of H2SO2 :

  • It is used in the manufacture of hundreds of other compounds and also in many industrial processes.
  • Manufacture of fertilizers.
  • Petroleum refining and manufacture of pigments, paints and dyestuff intermediates.
  • Detergent industry.
  • Metallurgical applications.
  • Storage batteries and so on.

Group 17 Elements: Fluorine, chlorine, .bromine, iodine and astatine are the members of Group 17. They are collectively called halogens (sea-salt producers)

→ Occurrence: Fluorine is present as CaF2 (fluorspar) and Na3 AlF6 (cryolite). Seawater contains chlorides, bromides and iodides of sodium, potassium, magnesium and calcium. The deposits of dried up seas contain NaCl and carnallite, KCl. MgCl2,6Fl2O. Seaweeds contain 0.5% of iodine and Chile saltpetre contains up to 0.2% of sodium iodate.

→ Electronic Configuration: All these elements have seven electrons in their valence shell [ns2np3] which is 1 electron less than the next noble gas.

→ Atomic and ionic radii: The halogens have the smallest atomic radii in their respective periods due to the maximum effective nuclear charge. The size of the anions is greater than the corresponding atoms. The atomic and ionic radii increase from top to bottom.

→ Ionisation Enthalpy: They have little tendency to lose electrons. Thus they have very high ionisation enthalpy. I.E. decreases from top to bottom.

→ Electronegativity: They have high electronegativities. It decreases from top to bottom. Fluorine is the most electronegative element in the periodic table. [F = 4.0]

→ Electron Gain Enthalpy: Halogens have maximum negative- electron gain enthalpy in their corresponding periods. It becomes less negative down the group. Electron gain enthalpy of F is less than that of Cl due to the compact size of F.

→ Physical Properties: F2 and Cl2 are gases. Br2 is a liquid and I2 is solid. They are all diatomic. M.pts and B.pts increase from top to bottom. F2 is yellow, Cl2 is greenish-yellow, Br2 is red and I2 violet in colour.

F2 has a smaller enthalpy of dissociation as compared to Cl2.

→ Chemical Properties:
Oxidation States and Trends in Chemical Reactivity: All the halogens exhibit a -1 oxidation state. However, chlorine, bromine and iodine exhibit +1, + 3, +5 and +7 oxidation states also as explained below:
The p-Block Elements 12 Notes Chemistry 47
Table: Atomic and Physical Properties of Halogens (Group 17)
The p-Block Elements 12 Notes Chemistry 48
aRadioactive; bPauling scale; cFor the liquid at temperatures (K) given in the parentheses; dsolid; eThe half-cell reaction is X2(g) + 2e– → 2X–(aq).
The p-Block Elements 12 Notes Chemistry 49
The higher oxidation states of chlorine, bromine and iodine are realised mainly when the halogens are in combination with the small and highly electronegative fluorine and oxygen atoms, e.g., in interhalogens, oxides and oxoacids.

The oxidation states of +4 and +6 occur in the oxides and oxoacids of chlorine and bromine. The fluorine atom has no d-orbitals in its valence shell and therefore cannot expand its octet. Being the most electronegative, it exhibits only a -1 oxidation state.

All the halogens are highly reactive. They react with metals and non-metals to form halides. The reactivity of the halogens decreases down the group.

The ready acceptance of an electron is the reason for the strong oxidising nature of halogens. F2 is the strongest oxidising halogen and it oxidises other halide ions in solution or even in the solid phase.

In general, a halogen oxidises halide ions of higher atomic number.
F2 + 2X– → 2F + X2 (X = Cl, Br or I)
Cl– + 2X– → 2CT + X2 (X = Br or I)
Br2 + 2I– → 2Br + I2

The decreasing oxidising ability of the halogens in aqueous solution down the group is evident from their standard electrode potentials which are dependent on the parameters indicated below:
The p-Block Elements 12 Notes Chemistry 50
The relative oxidising power of halogens can further be illustrated by their reactions with water. Fluorine oxidises water to oxygen whereas chlorine and bromine react with water to form corresponding hydrohalic and hypohalous acids.

The reaction of iodine with water is non-spontaneous. In fact, I– can be oxidised by oxygen in an acidic medium; just the reverse of the reaction observed with fluorine.
2F2 (g) + 2 H2O (l) → 4H+ (aq) + 4 F (aq) + O2 (g)
X2 (g) + H2O (l) → HX (aq) + HOX (aq) (where X = Cl or Br)
4I– (aq) + 4H+ (aq) + O2 (g) → 2I2 (s) + 2 H2O (l)

Anomalous behaviour of Fluorine: It is due to

  1. Highest electronegativity and Ionisation enthalpy in Group 17.
  2. Small size.
  3. Non-availability of d-orbitals.
  4. The low bond dissociation energy of the F-F bond.

1. Reactivity towards hydrogen: They all react with hydrogen to give hydrogen halides, but an affinity for hydrogen decreases from F to I.

The acidic strength is in order HF < HCl < HBr < HI and stability is under HF > HCl > HBr > HI.

2. Reactivity towards oxygen: Halogens form many oxides with oxygen but most of them are unstable. F forms OF2 and O2F2, but only OF2 is stable. Oxides of Cl, Br, I am powerful oxidizing agents.

3. Reactivity towards metals
Mg + Br2 (l) → MgBr2(s)
The ionic character of halids decreases in the order MF > MCI > MBr > MI.

4. Formation of interhalogen compounds: They form interhalogen compounds among themselves of the type AB, AB3, AB5, AB7 where A = larger size halogen and B = smaller size halogen.

Chlorine, Cl2:
Preparation:
1. By heating MnO2 with cone. HCl
The p-Block Elements 12 Notes Chemistry 51
However a mixture of common salt and cone. H2SO4 is used in place of HCl.
2 NaCl + MnO2 + 3 H2SO4 → 2 NaHSO4 + MnSO4 + 2H2O + Cl2

2. By the action of HC1 on KMn04
2 KMnO4 + 16HCl → 2 KCl + 2 MnCl2 + 5 Cl2 + 8 H2O

Manufacture of Cl2:
1. Deacon’s process:
The p-Block Elements 12 Notes Chemistry 52
2. Cl2 is obtained by the electrolysis of blue solution.

Properties:
1. Greenish-yellow gas with a pungent smell.

2. 2.5 times heavier than air.

3. Can be liquified easily into greenish-yellow liquid.

4. Soluble in water.

5. It reacts with a number of metals and non-metals and other compounds.
2Al + 3Cl2 → 2Al Cl3
2 Na + Cl2 → 2NaCl
2 Fe +3 Cl2 → 2FeCl3
P4 +6 Cl2 → 4PCl
S3 +4 Cl2 → 4 S2Cl2
H2 + Cl2 → 2HCl
H2S + Cl2 → 2HCl + S
C10H16 + 8 Cl2 → 16HCl + 10 C.
8NH3 (excess) + Cl2 → 6NH4Cl + N2
NH2  + 3Cl2 (excess) → NCl3 + 3HCl
The p-Block Elements 12 Notes Chemistry 53
6. Chlorine dissolved in water on standing loses its yellow colour due to the formation of HCl and HOCl. Hypochlorous acid (HOCl) so formed, gives nascent oxygen which is responsible for oxidising and bleaching properties: Its oxidising properties are:

(a) 2 FeSO4 + H2SO4 + Cl2 → Fe2(SO4)3 + 2 HCl
Na2SO3 + Cl2 + H2O → 4 Na2SO4 + 2 HCl
SO2 + 2H2O + Cl2 → 4 H2SO4 + 2HCl
I2 + 6 H2O + 5 Cl2 → 2 HIO3 + 10 HCl.

(b) It is a powerful bleaching agent due to oxidation. It is permanent.
The p-Block Elements 12 Notes Chemistry 54
Uses:

  1. For bleaching wood pulp, cotton and textiles.
  2. In the extraction of gold and platinum.
  3. Manufacture of dyes, drugs, DDT, refrigerants etc.
  4. In sterilising water.

Hydrogen Chloride, HCl:
Preparation-Lab.
Method:
2 NaCl + H2SO2  → Na2SO4 + 2 HCl cone.

Properties:

  1. It is a colourless gas with a pungent smell.
  2. Highly soluble in water.
  3. Can be liquified easily to a colourless liquid and solidified to a white crystalline solid.
  4. It ionises in an aqueous solution.
    HCl + H2O (l) → 4 H3O+ (aq) + Cl– (aq); Ka = 107
    The high value of Ka shows it is a strong acid in water.
  5. Reaction with NH3
    NH3 + HCl → NH4Cl (White dense fumes)
  6. 3 parts of cone. HCl and one part of cone. HNO3 on mixing give aqua regia which is used to dissolve, Au, Pt.
    Au + 4H+ + NO3 + 4 Cl– → AUCl4– + NO + 2H2O
    3Pt + 16H+ + 4NO3– + 18Cl– → 3PtCl62- + 4NO + 8H2O .
  7. Reaction with salts:
    Na2CO3 + 2HCl → 2 NaCl + H2O + CO2 ↑
    NaHCO3 + HCl → NaCl + H2O + CO2 ↑
    Na2SO3 + 2HCl → 2 NaCl + H2O + SO2 ↑

Uses of HCl:

  • Manufacture of Cl2, NH4Cl and glucose from com starch.
  • Extracting glue from bones and purifying bone black.
  • In medicine and as a lab. reagent

Table: Oxo-Acids of Halogens
The p-Block Elements 12 Notes Chemistry 55
Structures of Oxoacids:
The p-Block Elements 12 Notes Chemistry 56
Inter Halogen Compounds:
The p-Block Elements 12 Notes Chemistry 57
Some Properties of Interhalogen Compounds:
The p-Block Elements 12 Notes Chemistry 58

Uses:

  • Interhafogen compounds are very useful fluorinating agents.
  • They can be used as non-aqueous solvents.
  • ClF3 and BrF3 are used for the production of UF6 in the enrichment of 236U.
    U (s) + 3 ClF3 (l) → UF6(g) + 3 Cl F (g) argon (Ar)

Group 18 Elements: Group 18 Elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). Because of ns2nph structure [1s2 for He], They are chemically unreactive. They are called noble gases.

→ Occurrence: Except radon (Rn) which is radioactive, all noble gases occur in the atmosphere in traces. Noble gases constitute 1 % (by volume) of dry air. He is present in pitch blende, monazite, cleveite. Radon is obtained as a decay product of 226Ra.
22688Ra → 22286Ra + 42He

→ Electronic Configuration: All noble gases have ns2np6 electronic configuration except He which is 1s2.

→ Ionisation Enthalpy: They have very high I.E. which decreases down the group.

→ Atomic radii: They increase down the group with an increase in at. number.

→ Electron Gain Enthalpy: They have large positive values because of their stable electronic configuration. They have no tendency to accept electrons.

Physical Properties:

  1. These gases are monoatomic.
  2. They are colourless, odourless and tasteless.
  3. They are sparingly soluble in water.
  4. Due to weak dispersion forces, they have very low m.pts and b. pts.
  5. He has the lowest B.pt (4.2 K) of any known substance.

→ Chemical Properties: In general, noble gases are least reactive. It is due to

  1. Stable electronic configuration of ns2np6 (or 1s2 for He).
  2. They have high Ionisation enthalpy and more positive electron gain enthalpy,

Neil Bartlett prepared the first compound of Xe: red coloured Xe+ Pt F6– by mixing PtF6– and Xenon. The compounds of Kr are fewer. He, Ne and Ar are not found to form any true compounds. Only KrF2 has been studied. Compound involving Rn viz. RnF2 has been identified but not isolated.

Xenon-fluorine Compounds: Xenon forms three binary compounds with fluorine: XeF2, XeF4, XeF6 by the direct combination of elements under appropriate experimental conditions.
The p-Block Elements 12 Notes Chemistry 59
Xenon-oxygen compounds: Xenon and oxygen form XeO3. Partial hydrolysis of XeF4 and XeF6 gives oxyfluorides XeOF4 and XeO2F2.
The p-Block Elements 12 Notes Chemistry 60
The p-Block Elements 12 Notes Chemistry 61
structures of. (a) XeF2, (b) XeF4, (c) XeF6, (d) XeOF4 and (e) XeO3
XeO3 is a colourless explosive solid and has a pyramidal molecular structure. XeOF4 is a colourless volatile liquid and has a square pyramidal molecular structure.

Uses: He is used in filling balloons because He is a light and non-inflammable gas. It is used in gas-cooled nuclear reactors. Liquid He is used in low temp, physics. It is used in the driving apparatus.

Neon is used in discharge tubes and fluorescent bulbs for display purposes. Argon is mainly used to provide an inert atmosphere in high-temperature metallurgical processes.

There are no significant uses of Xenon and Krypton. They are used in light bulbs designed for special purposes.

Vibrio Cholerae

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Vibrio Cholerae

Vibrio is one of the curved rod bacteria, prominent in the Medical Bacteriology. They are present in marine environment and surface waters worldwide.

Vibrio is a member of the family Vibrionaceae. The most important member of this genus is Vibrio cholerae, the causative agent of cholera. The term Vibrio is derived from Vibrare (Latin word) which means “to shake or vibrate” and the word Cholera is derived from Chole (Greek word) which means, “to bile”.
Vibrio cholerae img 1

Morphology

Vibrio cholerae is gram negative, curved or comma shaped, (1.5um × 0.2 – 0.4um in size) non – capsulated. The organism is very actively motile with a single polar flagellum and the characteristic movement is called as darting motility. In stained smears of mucus flakes from acute cholera patients, the Vibriois seen
arranged in parallel rows. This was described by Robert Koch as “fish in stream” appearance.

Culture Characteristics

Vibrio cholera is strongly aerobic. It grows best in alkaline media with the optimum temperature 37°C and pH 8.2. It is nonhalophilic, therefore, cannot grow in media with a concentration of sodium chloride more than 7% (Figure 7.17). Some of the media in which Vibrio cholerae are cultivated are tabulated below
in Table 7.16.

Table 7.16: Colony morphology of Vibrio cholerae on various media

Media

Colony morphology
Nutrient agar The colonies are moist, translucent round disks (1-2mm in diameter) with a bluish tinge in transmitted light.
MacConkey agar The colonies are colorless at first but become reddish on prolonged incubation due to late fermentation of lactose.
Thiosulphate citrate bile sucrose sugar (pH 8.6) It is used as a selective medium for isolation of Vibrios. It produces large yellow convex colonies due to sucrose fermentation.

Enterotoxin

Vibrios multiplying on the intestinal epithelium produce an enterotoxin called Cholera toxin. It is also known as Choleragen (or CT). This toxin molecule is approximately 84,000 Dalton and consists of two major subunits namely A and B There is only one subunit in A (1A) whereas there are five subunits in B (5B) (Figure 7.18).
Vibrio cholerae img 2

Mode of Action

  • The B (binding) units of enterotoxin get attached to the GM1 (Ganglioside membrane receptors I) on the surface of jejunal epithelial cells. (target cells).
  • The A (active) subunits then enters the target cell and dissociates into 2 fragments, A1 & A2. The A2  fragment links biologically active A1 fragment to the B – subunit.
  • The A1 fragment causes prolonged activation of cellular adenylate cyclase which in turn accumulates CAMP in the target cell. This leads to outpouring of large quantities of water and electrolytes into small intestinal lumen. Thus, resulting in profuse watery diarrhea.

Pathogenesis

The pathogenic mechanism of Vibrio choleraeis discussed below in flowchart 7.7.
Source of Infection – contaminated water or food
Route of entry – fecal – oral route
Site of infection – small intestine
Incubation period – few hours to 5 days (usually 2 – 3 days)
Vibrio cholerae img 3

Clinical Feature

Dehydration, anuria (absence of urine excretion), muscle cramps, hypokalemia (low blood potassium) & metabolic acidosis (low serum concentration of bicarbonates).

Laboratory Diagnosis

Specimen: Stool

Direct microscopy:

It is not a reliable method for rapid diagnosis, the characteristic darting motility of the vibrio can be observed under dark – field microscope.

Culture:

Stool sample is directly inoculated on MacConkey agar and TCBS agar. The plates are examined after overnight incubation at 37°C for typical colonies of Vibrio cholera, and the colonies are identified by gram staining and oxidasetest.

Prophylaxis

1. General Measures:

  • Purification of water supplies
  • Improvement of environment sanitation
  • Infected patients should be isolated, and their excreta must be disinfected

2. Vaccines:

Two types of oral vaccines have been tried recently:

  • Killed oral whole cell vaccines
  • Live oral vaccines

Treatment

1. Oral Rehydrationtherapy:

The severe dehydration & salt depletion can be treated by oral rehydration therapy (as recommended by WHO).

2. Antibiotics:

It is of secondary importance, oral tetracycline was recommended for reducing the period of Vibrio excretion.

Salmonella typhi of Medical Bacteriology

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Salmonella typhi of Bacteriology

The genus Salmonella consists of bacilli that parasites the intestines of vertebrates and human beings. It causes Enteric fever, which includes Typhoid and Paratyphoid fever. The most important species of the genus is Salmonella typhi which causes typhoid fever.

Morphology

Salmonellae are Gram – negative rods (1 – 3µm × 0.5 µm in size). They are motile with peritrichous flagella, non – capsulated and non – sporulated (Figure 7.14).
Salmonella typhi of Bacteriology img 1

Cultural Characteristics

They are aerobic and facultative anaerobe, optimum temperature – 37°C and pH is 7 – 7.5. They grow on the following media and show the following characteristic colony morphology (Table 7.12).

Table 7.12: Colony morphology of Salmonella typhi

Media

Colony Morphology
Nutrient Agar Colonies are large, circular, smooth, translucent
MacConkey Agar Colourless colonies (non – lactose fermenters)
SS – Agar Colourless colonies with black centered.

Pathogenicity

Salmonella typhi causes typhoid fever and its pathogenesis is discussed in flowchart 7.6.

Source of infection – food, feces, fingers, flies
Route of entry – faecal oralroute (ingestion)
Incubation period – 7 – 14 days
Salmonella typhi of Bacteriology img 2

Clinical Manifestations

  • The illness is usually gradual, with headache, malaise (feeling of discomfort), an2orexia (loss of appetite), coated tongue, abdominal discomfort with either constipation or diarrhea.
  • Hepatosplenomegaly (enlargement of liver and spleen), step ladder pyrexia (continuous fever) and rose – spots (during 22nd or 3rd week).

Laboratory Diagnosis

Specimens:

Blood, stool and urine are the clinical samples collected from typhoid patients. The selection of relevant specimen depends upon duration of illness, which is very important for diagnosis (Table 7.13 & Figure 7.15).

Table 7.13: Specimen collection for typhoid

Duration of disease

Specimen examination

% Positivity
1st Week Blood culture 90
22nd Week Blood culture
Faeces culture
Widal test		 75
50
Low titer
3rd Week Widal test
Blood culture
Faeces culture		 80 – 100
60
80

Salmonella typhi of Bacteriology img 3

The bacteriological diagnosis of enteric fever consists of the following methods, which are:

  • Isolation of the bacilli
  • Demonstration of antibodies

Isolation of the bacilli

The typhoid bacilli are isolatedfrom the following clinical specimens which are tabulated (Table 7.14).

Table 7.14: Isolation method of typhoid bacilli from various clinical speciments.

Demonstration of Antibodies:

Slide – agglutination: The isolate is identified by slide agglutination with ‘O’ and ‘H’ antisera.

Widal Test:

It is an agglutination test for detection of agglutinins ‘H’ and ‘O’ in patients with enteric fever. Salmonella antibodies start appearing in the serum at the end of 1st week and rise sharply during the 3rd week of enteric fever.

Prophylaxis

Various types of vaccine and their doses are given in Table 7.15.

Table 7.15: Various types of vaccine and their doses.

Vaccine

Doses
TAB – Vaccine 2 doses of 0.5 ml at an interval of 4-6 weeks
Typhoral 3 doses on alternate days. It gives 65-96% protection for 3-5 years and is safe
Typhin – Vi A single dose of 25µg

Treatment and Control Measures

  • Antibacterial therapy has been very effective in the treatment of patients.
  • Ampicillin, amoxicillin and cotrimoxazole are useful in the treatment of typhoid fever.
  • At present, ciprofloxacin is the drug of choice.
  • Typhoid fever can be effectively controlled by sanitary measures for disposal of sewage, clean water supply and supervision of food processing and handling.

Medical Shigella dysenteriae

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Medical Shigella dysenteriae

The genus Shigellaare exclusively parasites of human intestine and other primates. Shigella dysenteriae is the causative agent of bacillary dysentery or shigellosis in humans. It is a diarrheal illness which is characterized by frequent passage of bloodstained mucopurulent stools.

The four important species of the genus Shigella are: Shigella dysenteriae, Shigella flexneri, Shigella sonnei and Shigella boydii.

Morphology

Shigella are short, Gram negative rods (0.5µm × 1-3 µm in size). They are non – motile, non – sporing and non – capsulated (Figure 7.12).
Medical Shigella dysenteriae img 1

Cultural Characteristics

  • They are aerobes and facultative anaerobes. Optimum temperature is 37°C and optimum pH – 7.4.
  • They can be grown on the following media and show the characteristic colony morphology (Table 7.10 & Figure 7.13)

Table 7.10: Colony morphology of Shigella

Media

Colony Morphology
Nutrient Agar Colonies are circular, convex smooth and translucent
MacConkey Agar Colourless colonies
SS – Agar Colourless colonies

Medical Shigella dysenteriae img 2

Toxins

Shigella dysenteriae produces toxins, which is of 3 types, namely, endotoxin, exotoxin and verocytotoxin. The mode of action of these toxins is illustrated in the Table 7.11.

Table 7.11: Various toxins of Shigelladysenteriae

Toxins

Mode of Action
Endotoxin It is released ater autolysis, it has irritating effect on intestinal wall which causes diarrhea and subsequently intestinal ulcers.
Exotoxin It is a powerful toxin and acts as Enterotoxin as well as neurotoxin
As Enteroxin – It induces fluid accumulation
As Neurotoxin – It damages the endothelial cells of small blood vessels of CNS which results in polyneuritis and coma
Vero cytotoxin It acts on Vero cells

Pathogenesis

The pathogenic mechanism of Shigella dysenteriaeis discussed below in flowchart 7.5.

Source of Infection – Patient or carriers
Route of entry – faecal – oral route
Site of infection – Large intestine
Incubation Period – Less than 48 hours (1-7 days)
Mode of transmission – Food, finger, faeces and flies

Clinical Manifestations

  • Frequent passage of loose, scanty faeces containing blood and mucus.
  • Abdominal cramps and tenesmus (straining to defecate).
  • Fever and vomiting.
  • Hemolytic uremic syndrome (It is a condition caused by the abnormal destruction of red blood cells)

Laboratory Diagnosis

Specimens:
Fresh stool is collected.

Direct Microscopy:
Saline and Lugol’s iodine preparation of faeces show large number of pus cells, and erythrocytes.

Culture:
For inoculation, it is best to use mucus flakes (if present in the specimen) on MacConkey agar and SS agar. After overnight incubation at 37°C, the plates are observed for characteristic colonies, which is confirmed by Grams staining and biochemical reactions.

Treatment and Prevention

  • Uncomplicated shigellosis is a self – limiting condition that usually recovers spontaneously.
  • In acute cases, oral rehydration therapy (ORT) is done.
  • In all severe cases, the choice of antibiotic should be based on the sensitivity of prevailing strain.
  • Many strains are sensitive to Nalidixic acid and Norfloxacin.
  • Improving personal and environmental sanitation.
  • The detection and treatment of patients and carriers.

Clostridium tetani of Medical Bacteriology

Learninsta presents the core concepts of Microbiology with high-quality research papers and topical review articles.

Clostridium tetani of Medical Bacteriology

The genus Clostridium consists of anaerobic, spore forming Gram positive bacilli. The spores are wider than the bacterial bodies, giving the bacillus a swollen appearance resembling a spindle. The name Clostridium is derived from the word ‘kluster’ (a spindle).

Most species are saprophytes found in soil, water and decomposing plant and animal matter. Some of the pathogens are normal flora of intestinal tract of human and animals.

The genus Clostridium includes bacteria that causes 3 major diseases of human – Tetanus, gas gangrene and food poisoning. Clostridium pathogenicity is mainly due to production of a powerful exotoxin.

Clostridium of medical importance may be classified based on diseases they produce, which is given the Table (7.7).

Table 7.7: Clostridium sp, causing pathogenic diseases.

Organisms

Diseases
Clostridium tetani Tetanus
Clostridium perfringens Gas gangrene
Clostridium botulinum Food poisoning

Morphology

They are Gram positive spore forming rods. The spores are spherical and terminal in position giving a drumstick appearance. They are motile and non – capsulated.

Culture Characteristics

  • They are obligate anaerobes, optimum temperature is 37°C and pH is 7.4.
  • It grows on ordinary media, but growth is enhanced by addition of blood and serum. Clostridia tetani grows on the following media and show the characteristic colony morphology (Table 7.8).

Table 7.8: Colony characteristics of Clostridium tetani

Media

Colony Morphology
Blood agar They produce α – hemolysis which subsequently develop into β – hemolysis (due to tetanolysis) it produces swarming growth.
Cooked meat broth (CMB) Growth occurs as turbidity with gas formation. The meat is not digested but becomes black on prolonged incubation.

Toxins

Clostridium tetani produces two distinct toxins namely,

  • Tetanolysis (haemolysin)
  • Tetanospasmin (neurotoxin)

Tetanolysis

  • Heat labile and oxygen labile toxin.
  • It lysis erythrocytes and also acts as neurotoxin.

Tetanospasmin

  • It is heat labile and oxygen stable powerful neurotoxin.
  • It is protein in nature. consisting of a large polypeptide chain (93,000 Dalton) and a smaller polypeptide chain (52,000 Dalton) joined by a disulphide bond.
  • Mode of Action: Tetanospasminis a neurotoxin, which blocks the release of inhibitory neurotransmitters (glycine and gamma – amino butyric acid) across the synaptic junction.
  • The toxin acts presynaptically, the abolition of spinal inhibition causes uncontrolled spread of impulses in CNS (Central Nerves System).

This results in muscle rigidity and spasms (due to the simultaneous contraction of agonists and antagonists, in the absence of reciprocal inhibition (Figure 7.11).
Clostridium tetani of Medical Bacteriology img 1

Pathogenesis

Clostridium tetani is the causative organism of tetanus or lock jaw disease. pathogenesis of Clostridium tetani was discussed in detail in flowchart 7.4.

Source of infection – Soil, dust, faeces.
Route of entry – Through wound
Incubation period – 6 – 12 days

Clinical Feature

It includes, pain and tingling at the site of wound, Lock jaw ortrismus (It is reduced opening of the jaws), Risus sardonicus (mouth kept slightly open), Dysphasia (impairment of the ability to speak or to understand language) and acute asphyxia.

Laboratory Diagnosis

Specimens:
Wound swab, exudates or tissue from wound.

Microscopy:
Gram staining shows Gram positive bacilli with drumstick appearance.

Culture:
The clinical specimen is inoculated on blood agar and incubated at 37°C for 24-48 hours under anaerobic conditions. The colonies are confirmed by gram staining, where it shows gram positive bacilli with drumstick appearance.

Treatment

Tetanus patients are treated in special isolated units, to protect them from noise and light which may provoke convulsions. The spasm can be controlled by diazepam (0.1 – 0.2 mg/kg) injection. Antibiotic therapy with pencilin or metroniadazole should be done for a week or more.

Prophylaxis

It is done by the following methods, which are as follows.

a. Surgical prophylaxis:

It aims at removal of foreign body, blood clots and damaged tissue in order to prevent anaerobic conditions favorable for the
germination of spores.

b. Immunoprophylaxis:

Tetanus is a preventable disease. Immune prophylaxis is of 3 types, which is given in the (Table 7.9).
Table 7.9: Immunization for tetanus.
Clostridium tetani of Medical Bacteriology img 2

General Principles and Processes of Isolation of Elements Class 12 Notes Chemistry Chapter 6

By going through these CBSE Class 12 Chemistry Notes Chapter 6 General Principles and Processes of Isolation of Elements, students can recall all the concepts quickly.

General Principles and Processes of Isolation of Elements Notes Class 12 Chemistry Chapter 6

The extraction and isolation of an element from its combined form involves various principles of chemistry. Metallurgy is the scientific and technological process of extracting a metal from its ore. The natural materials in which the metals or their compounds occur in the earth are called minerals. The mineral from which the metal is extracted conveniently and economically is called an ore. Ores are usually contaminated with earthly or undesired materials known as Gangue.

The extraction and isolation of metals from their respective ores involve the following major steps :

  1. The concentration of the ore
  2. Isolation of the metal from its concentrated ore, and
  3. Purification of the metal.

Principle Ores of Some Important Metals:
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 1
Among metals, aluminium is the most abundant. For the purpose of extraction, bauxite is chosen for aluminium. For iron, usually oxide ores [Haematite Fe203] are taken. Before proceeding for concentration, ores are graded and crushed to a reasonable size.

Concentration Of Ores: Removal of the unwanted materials (e.g. sand, clays etc.) from the ore is called concentration, dressing, or benefaction. Unwanted impurities present in the ore are called gangue.

The nature of the impurities, the type of the metal and the environmental factors are taken into consideration.
(a) Hydraulic Washing: it is based on the difference in gravities of the ore and the gangue particles. It is, therefore, a type of gravity separation. When a stream of water is run through the powdered ore, the lighter gangue particles are washed away and heavier ore particles settle down.

(b) Magnetic Separation: This procedure is based on the difference in the magnetic properties of the ore and impurities present in it. When passed over the conveyer belt of a magnetic roller, magnetic particles settle in a heap nearer and non-magnetic impurities a bit away, as shown below:
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 2
Magnetic Separation

Froth Floatation Process: This process is used for removing gangue from sulphide ores only. Powdered sulphide ore is mixed with water to which Collectors (e.g. pine oil, fatty acid, xanthates etc.) enhance the non-wettability of the mineral particles and froth stabilizers (e.g. cresols, aniline) which stabilize the froth ore added. The mineral particles become wet by oils while the gangue particles by water.

A rotating paddle agitates the mixture and draws air in it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off from where ore particles are recovered after drying it
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 3
Froth Flotation Process

Leaching: This process consists of treating the powdered ore with a suitable reagent (such as acids bases or other chemicals) which can n selectively dissolve the ore but not the impurities.

In Baeyer’s process, pure aluminium oxide is obtained from the bauxite ore (which contains impurities of Fe2Os and silicates) by treating the powdered ore with a 45% solution of NaOH when alumina dissolves leaving behind impurities like Fe203 which are filtered off.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 4
Na [Al(OH)4] or NaAlO., is neutralized by CO2 when Al(OH)3 gets precipitated.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 5
Al(OH)3, obtained above is filtered, washed and finally heated to about 1473 K to get pure alumina Al2O3
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 6
Extraction of Crude Metal From Concentrated Ore: The concentrated ore must be converted into a form that is suitable for a reduction. Sulphide ore is usually converted into its oxide before reduction. Oxides are easier to reduce.

Two steps are involved
(a) Conversion of the concentrated ore into oxide ore
(b) Reduction of the metal oxide into metal

(a) Conversion To Oxide:
1. Calcination: It is the process of converting ore into its oxide by heating it strongly below its melting point either in the absence or limited supply of air. Volatile matter is driven off.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 7
2. Roasting: It is the process of converting ore into its metallic oxide by heating strongly at a temperature insufficient to melt in excess of air.
2 ZnS + 3O2 → 2 ZnO + 2 SO2
2 PbS + 3O2 → 2 PbO + 2SO2
2 Cu2S + 3O2 → 2 Cu2O + 2 SO2

(b) Reduction of oxide to the metal: It is done with a suitable reducing agent (C or CO or even another metal)
MxO + yC → xM + yCO

Thermodynamic Principles Of Metallurgy: The change in Gibbs energy ΔG is given by
ΔG = ΔH – TΔS …(1)
where ΔH = Enthalpy change at temperature T
ΔS = Entropy change at temperature T

Also ΔG° = -RT ln K. ……….(2)
where R = Gas constant;
K = Equilibrium constant.
The reaction will proceed if ΔG° is negative K in that case will be positive.

This happens only when the reaction proceeds towards products.
1. When the value of ΔG° is negative in equation (1) then only the reaction will proceed. If ΔS is positive, on increasing the temperature (T), the value of TΔS would increase (ΔH < TΔS) and then ΔG will become -ve.

2. If reactants and products of two reactions are put together in a system and the net ΔG of the possible reactions is – ve, the overall reaction will occur. So the process of interpretation involves the coupling of the two reactions, getting the sum of their ΔG and looking for its magnitude and sign. Such coupling is easily understood through Gibbs energy (ΔG°) vs – T plots for the formation of the oxides.

H.J. T Ellingham gave a graphical representation of Gibbs energy. It provides a sound basis for considering the choice of reducing agent in the reduction of oxides. Such a diagram helps us in predicting the feasibility of the thermal reduction of ore.

The reducing agent forms its oxide when the metal oxide is reduced. The role of the reducing agent is to provide ΔG° negative and large enough to make the sum of ΔG° of the two reactions (oxidation of the reducing agent and reduction of the metal oxide) negative.

As we know, during reduction, the oxide of a metal decomposes.
MxO (s) → xM (Solid or Liquid) + \(\frac{1}{2}\) O2(g) ……..(3)

The reducing agent takes away the oxygen.
xM (s or l) + \(\frac{1}{2}\) O2 → MxO(s) ……[ΔG°(M, MxO) ………(4)

If reduction is carried out through equa lion (3), the oxidadion of the reducing agent (e.g. C or CO) will be as:
C(s) + \(\frac{1}{2}\) Oz(g) → CO(g) …………[ΔG(C, CO)]…..(5)
CO(g) + \(\frac{1}{2}\) Oz(g) → CO2(g)……[ΔG(C, CO)]…(6)

If carbon is taken, there may be complete oxidation to CO2
\(\frac{1}{2}\) C(s)+ \(\frac{1}{2}\)O2 (g) → \(\frac{1}{2}\)CO2(g) ….[2 ΔG(C, CO)]…(7)

On subtracting equation (4), we get
MxO(s) + C(s) → xM(s or l) +CO(g) …(8)
MxO (s) + C (s) → xM (s or l) + CO2 (g) …(9)
MxO (s) + \(\frac{1}{2}\)C(s) → xM (s or l) + \(\frac{1}{2}\)CO2 (g). …..(10)

These reactions describe the actual reduction of the metal oxide MxO that is to be accomplished.
Increasing T (Heating) favours a negative value of ΔrG°. Therefore, the temperature is chosen such that the sum of ΔrG° in the two combined redox process is negative.

Applications:
(a) Extraction of Iron from its Oxides: Concentrated oxide ores of iron are mixed with limestone and coke and fed into a Blast furnace from the top. Here coke reduces oxide to the metal as follows:
FeO(s) + C(s) → Fe(s or l) + CO(g) ……….(11)

In two steps:
1. FeO(s) → Fe(s) + \(\frac{1}{2}\)O2 (g) [ΔG(FeO, Fe)] …….(2)
2. C(s) + \(\frac{1}{2}\) O2 (g) → CO(g) [ΔG(C, CO)] ……..(3)

From (12) and (13), The ne.t Gibbs energy change becomes
ΔG(C, CO) + ΔG(FeO, Fe) = ΔrG ……….(14)

∴ The resultant reaction will take place when the r.h.s. of equation (14) becomes negative.

The reactions occurring in the Blast furnace at different temperatures are as follows:
At 500 – 800 K (lower temp, range)
3 Fe2O3 + CO → 2 Fe3O4 + CO2
Fe3O4 + 4CO → 3 Fe + 4 CO2
Fe2O3 + C0 → 2Fe + CO2

At 900 -1500 K (higher temp, in the blast furnace)
C + CO2 → 2CO
FeO + CO → Fe + CO2

Limestone is also decomposed to CaO which removes silicate impurity of the ore as slag. The slag is in a molten state and separates out from iron.
CaCO3 (s) → CaO (s) + CO2 (g)
CaO (s) + SiO2 (s) → CaSiO2  (fusible slag)

Iron obtained from Blast furnace contains 4% carbon and many impurities in smaller amount (e.g. S, P, Si, Mn) is called pig iron. Cast iron is different from pig iron. It has a slightly lower carbon content (3%) and is extremely hard and brittle.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 8
Blast Furnace

Further Reductions: Wrought iron or malleable iron is the purest form of commercial iron and is prepared from cast iron by oxidising

impurities in a reverberatory furnace lined with haematite. This haematite oxidises carbon to carbon monoxide :
Fe2O3 + 3 C → 2 Fe + 3CO

Limestone is added as a flux and sulphur, silicon and phosphorus are oxidised and passed into the slag. The metal is removed and freed from the slag by passing through rollers.

(b) Extraction of Copper from Cuprous Oxide [Copper (I) Oxide]: Most of the copper ores are sulphide ores, concentrated sulphide ores are roasted/smelted to give oxides.
2 Cu2S + 3 O2 → 2 Cu2O + S

The oxide can then be easily reduced to give Cu metal.
Cu20 + Ccoke → 2 Cu + CO

In the actual process, the ore is heated in a reverberatory furnace after mixing with silica.
In the furnace, iron oxide slags off’ as iron silicate and copper is produced in the form of copper matte which contains Cu2S and FeS.
FeO + SiO2 → Fe Si O3(slag)

In the silica-lined convertor, copper matte is charged. Some silica is added and a hot air blast is blown when the following reactions take place.
2 FeS + 3O2 → 2 FeO + 2SO2
FeO + SiO2 → FeSiO3
2 Cu2S + 3O2 → 2 Cu2O + 2 SO2
2 Cu2O + Cu2S → 6 Cu + SO2
The solidified copper obtained has a blistered appearance due to the evolution of SO2 and so it is called blister copper.

(C) Extraction of Zinc from Zinc Oxide: Zinc oxide is reduced using coke
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 9
The metal is distilled off and collected by rapid chilling.

Electrochemical Principles Of Metallurgy: In electrolysis, metal ions in solution or molten form are reduced or by adding some reducing element. Here
ΔG° =. – n FE° ….(i)
where n = no. of electrons transferred
E° = Standard e.m.f. of the cell [redox couple]
F = Faraday = 96,500 C
ΔG° = Change in standard Gibbs energy.

More reactive metals have large negative values of the electrode potential. So their reduction is difficult. If the difference of two E° values corresponds to a positive E° and consequently negative ΔG° in the equation
1. above, then the less reactive metal will come out of the solution and more reactive metal will go into the solution.
Cu2+ (aq) + Fe (S) → Cu (S) + Fe2+ (aq)

Examples:
Metallurgy of Aluminium: Purified Al2O3 is mixed with Na3 AlF6 or CaF2 to, lower the melting point of the mix and to make the solution conductive. The fused matrix is electrolysed.
2 Al2O3 + 3C → 4 Al + 3 CO2

This process of electrolysis is widely known as the Hall-Fieroult process.

Steel cathode and graphite anode are used. The graphite anode is useful here for the reduction of oxide to the metal.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 10
Electrolytic cell for the extraction of aluminium

The electrolysis of the molten mass is carried out in an electrolytic cell using carbon electrodes. The oxygen liberated at the anode reacts with the carbon of the anode producing CO and CO2.This way for each kg of aluminium – produced, about 0.5 kg of carbon anode is burnt away.

The electrolytic reactions are:
Cathode: Al3+ (melt) + 3e– → Al (l)
Anode: C(s) + O2- (melt) → CO(g) + 2e–
C(s) + 2 O2- (melt) → CO2 (g) + 4e–

Copper from low-grade ores and scraps: Copper is extracted from low grades ores by Hydrometallurgy. It is leached out using acid or bacteria. The solution containing Cu2+ (aq) is treated with iron or H2.
Cu2+ (aq) + H2 (g) → Cu (s) + 2H+(aq)

Oxidation-Reduction: Some non-metals are extracted based on oxidation. Chlorine from prime solution is oxidized to Cl2.
2 Cl– (aq) + 2 H2O (l) → 2 OH– (aq) + H2 (g) + Cl2 (g)

In the extraction of gold and silver, metal is leached with CN–.
Ag → Ag+ + e– oxidation
Au → Au+ + e– oxidation

The metal is later recovered by the displacement method.
4 Au (s) + 8 CN– (aq) + 2H2O (aq) + O2 → 4 [Au (CN)2]– (aq) + 4 OH– (aq)
2 [Au (CN)2]– (aq) + Zn (s) → 2 Au (s) + [Zn (CN)4]2- (aq)
In this reaction zinc acts as a reducing agent.

Refining: To obtain metal of high purity and to remove the last traces of impurities from the extracted metal, they are subjected to refining.

It is based upon the difference in properties of the metal and the impurity.
Several techniques are listed below:

  1. Distillation,
  2. Liquation,
  3. Electrolysis,
  4. Zone refining,
  5. Vapour phase refining,
  6. Chromatographic methods.

1. Distillation: This is useful for low boiling metals like Zn and Hg.

2. Liquation: A low melting metal like tin (Sn) can be made to flow on a sloping surface leaving higher melting impurities.

3. Electrolytic Refining: Impure metal is made anode. A strip of pure metal is made the cathode. The electrolyte (bath) contains soluble salt of the same metal.
Anode: M → Mn+ + e–
Cathode: Mn+ + ne– → M

Copper is refined by the electrolytic method. Here acidified solution of copper sulphate acts as an electrolyte.
Anode: Cu(s) → Cu2+ + 2e
Cathode: Cu2+ + 2e → Cu(s)

4. Zone Refining: This method is based upon the principle that the impurities are more soluble in the melt than in the solid state of the metal. The molten zone moves along with the mobile heater fixed at one end of the impure metal. As the heater moves forward the pure metal crystallises out of the metal and the impurities pass on into the adjacent molten zone. At one end, impurities get concentrated. This end is cut off.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 11
Zone-Refining Process

Vapour Phase Refining: Mond’s Process for Nickel Refining
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 12
The carbonyl complex is subjected to a higher temperature so that it is decomposed to give pure metal.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 13
van Arkel Method for Refining Zirconium or Titanium: This method is very useful for removing all the oxygen and nitrogen present in the form of impurity in certain metals like Zr and Ti. The crude metal is heated in an evacuated vessel with iodine. The metal iodide, being more covalent, volatilises.
Zr + 2I2 → ZrI4.
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 14
Chromatographic Methods: This method is based on the principle that different components of a mixture are differently adsorbed on an adsorbent.

Column Chromatography: It is very useful for the purification of the elements which are available in minute quantities and the impurities are not very different in chemical properties from the element to be purified.

There are several chromatographic techniques such as

  1. Paper chromatography
  2. Gas chromatography

Uses of Aluminium, Copper, Zinc and Iron: Alloys containing Al are light and are very useful. A1 wires conduct electricity. It is used as a reductant.

Copper is used to making wires in the electrical industry. Several alloys of copper with Zn, Sn and Ni are largely used.
Zinc is used for galvanising iron. It is used as a reducing agent. Similarly different forms of iron: Cast iron, Wrought iron, Steel find wide applications.

A Summary of the Occurrence and Extraction of Some Metals is Presented in the following Table:
General Principles and Processes of Isolation of Elements 12 Notes Chemistry 15

Corynebacterium diphtheriae

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Corynebacterium diphtheriae

Several species of the genus Corynebacterium are normal flora of skin, upper respiratory tract (URT), urogenital and intestinal tract. The most important member of the genus is C. diphtheriae the causative agent of diphtheria, a localized inflammation of the throat with greyish white pseudomembrane and a generalized toxemia due to the secretion and dissemination of a highly potent toxin.

The name Corynebacterium diphtheria is derived from Greek word ‘Coryne’ – “Club shaped swellings” or “Knotted rod” ‘Diphthera’ – Leather.

Morphology

They are Gram positive slender rods, pleomorphic club shape or coryneform bacterium Non – motile, non – sporing and non – capsulated (Figure 7.9 a & b).
Corynebacterium diphtheriae img 1

The bacilli are arranged in a characteristic fashion in angular fashion resembling the letters V or L. This has been called Chinese letter or cuneiform arrangement (Figure 7.10).

They are club shaped due to the presence of metachromatic granules at one or both ends. These granules are composed of polymetaphosphates and represent energy storage depots.
Corynebacterium diphtheriae img 2

Cultural Characteristics

  • They are aerobic and facultative anaerobe. Optimum temperature is 37°C and pH 7.2.
  • They grow on the following media and show the characteristic colony morphology (Table 7.5).

Table 7.5: Colony Morphology of Corynebacterium diphtheriae on cultural media

Media

Colony Morphology
Loeffler’s Serum slope They glow on this medium very rapidly. Colonies appear after 6-8 hours of incubation. The colonies are small, circular white or creamy and glistening.
Tellurite Blood Agar Grey or black colonies. Based on colony morphology on tellurite medium, three main biotypes – Gravis, Intermedius and Mitis.

Toxin

• The pathogenicity is due to production of a very powerful exotoxin by virulent strains of diphtheria bacilli.
• The toxigenicity of diphtheria bacillus depends on the presence of a tox<sup>+</sup> gene which can be transferred from one bacterium to another by lysogenic bacteriophages, of which beta phage is the most important.

Properties

The diphtheria toxin is a heat – labile protein and has a molecular weight of about 62,000 Dalton. It consists of two fragments

  • Fragment A (24,000 Dalton) – It has all enzymatic activity.
  • Fragment B (38,000 Dalton) – It is responsible for binding the toxin to the target cells.

Mode of Action

The toxin acts by inhibiting protein synthesis, specifically fragment A inhibits polypeptide chain elongation in the presence of NAD by inactivating the elongation factor (EF – 2) the toxin has special affinity for myocardium, adrenal gland and nerve endings.

Pathogenicity

Source of infection – Airborne droplets
Route of entry – Upper respiratory tract
Incubation period – 3 – 4 days

Site of infection – Faucial (nasal, otitis, conjunctival, laryngeal, genital) diphtheria is most commonly seen in children of 2-10 years.

Faucial diphtheria is the most common type. The infection is confined to humans only. The toxin has both local (flowchart 7.3) as well as systemic effects.
Corynebacterium diphtheriae img 3
Flowchart 7.3: Localized effect of diphtheria toxin

Systemic effects

The toxin diffuses into the blood stream and causes toxemia. It has got affinity for cardiac muscle, adrenal and nerve endings. It acts on the cells of these tissues.

Clinical Manifestations

  1. Laryngeal obstruction, asphyxia (it is a condition of severe deficient supply of oxygen, causing suffocation).
  2. Diphtheritic myocarditis (inflammation of heart muscle), polyneuropathy (damage of multiple peripheral nerves), paralysis of palatine (the top part of the inside of the mouth) and ciliary muscles.
  3. Degenerative changes in adrenal glands, kidney and liver may occur.

Specimen:
Two swabs from the lesions are collected. One swab is used for smear preparationand other swab for inoculation on culturemedia.

Direct microscopy:
Smears are stained with both Gram stain and Albert stain.

  • Gram Staining – Gram positive slender rods were observed.
  • Albert staining – Club shaped with metachromatic granules were observed.

Culture:
The swabis inoculated on Loeffler’s serum slope, after overnight incubation at 37°C, the plates were observed for characteristic colonies, which are identified by gram staining.

Prophylaxis

Diphtheria can be controlled by immunization. Three methods of immunization are available (Table 7.6).
Corynebacterium diphtheriae img 4
Table 7.6: Immunization for diphtheria

Treatment

The specific treatment for diphtheria consists of administration of antitoxin with dose of 20,000-100,000 units of ADS intramuscularly and antibiotic therapy using penicillin.

Neisseria meningitidis (Meningococcus)

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Neisseria meningitidis (Meningococcus)

The genus Neisseria is included in the family Neisseriaceae (Figure 7.6). It contains two important pathogens Neisseria meningitidis and Neisseria gonorrhoeae, both the species are strict human pathogens. N. meningitides causes meningococcal meningitis (formerly known as cerebrospinal fever).

The word Meningitis is derived from Greek word ‘meninx’ means membrane and ‘it is’ means inflammation. It is an inflammation of meanings of brain or spinal cord. Bacterial meningitis is a much more severe disease than viral meningitis.

Morphology

They are Gram negative diplococci (0.6µm-0.8µm in size) arranged typically in pairs, with adjacent sides flattened. They are non – motile, capsulated (Fresh isolates). Cocci are generally intracellular when isolated from lesions (Figure 7.7).
Neisseria meningitidis (Meningococcus) img 1

Cultural Characteristic

They are strict aerobes, but growth is facilitated by 5-10% CO<sub>2</sub> and high humidity. The optimum temperature is 35°C-36°C and optimum pH is 7.4-7.6. They are fastidious pathogens, growth occurs on media enriched with blood or serum. They grow on the following media and show the characteristic colony morphology (Table 7.4).
Neisseria meningitidis (Meningococcus) img 2

Table 7. 4: Colony morphology of Neisseria Meningitides on media

Name of the Media

Colony Morphology
Chocolate agar Colonies are large, colorless to grey opaque colonies.
Mueller Hinton agar Colonies are small, round, convex grey, translucent with entire edges. The colonies are butyrous in consistency and easily emulsified.

Pathogenesis

N. meningitidis is the causative agent of meningococcal meningitis, also known as pyogenic or septic meningitis. Infection is most common in children and young adults. Meningococci are strict human pathogens. Human nasopharynx is the reservoir of N.meningitidis. The pathogenesis is dicussed in the
flowchart 7.2.

Source of infection – Airborne droplets
Route of entry – Nasopharynx
Site of infection – Meninges
Incubation period – 3 days

Flowchart 7.2: Pathogenesis of Neisseria Meningitides
Neisseria meningitidis (Meningococcus) img 3

Laboratory Diagnosis

Specimens:

CSF, blood, nasopharyngeal scrapings from petechiae lesions are the specimens collected from pyogenic meningitis patients.

Direct Microscopy:

CSF is centrifuged, and smear is prepared from the deposit for gram staining. Meningococci are Gram negative diplococci, present mainly inside polymorphs and many pus cells are also seen.

Culture:

The centrifuged deposit of CSF is inoculated on chocolate agar. The plate is incubated at 36°C under 5-10% CO2 for 18-24 hours. After incubation period, meningococcusis identified by gram staining, colony morphology and biochemical reactions. N. meningitides is catalase and oxidase positive (Figure 7.8).
Neisseria meningitidis (Meningococcus) img 4

Treatment and Prophylaxis

Penicillin – G is the drug of choice. In penicillin allergic cases, chloramphenicol is recommended.

  • Monovalent and polyvalent vaccines (capsular polysaccharide) induce good immunity in older children and adults.
  • Conjugate vaccines are used for children below the age of 2 years.

Streptococcus pyogenes (Flesh eating Bacteria)

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Streptococcus pyogenes (Flesh eating Bacteria)

The genus Streptococcus includes a large and varied group of bacteria. They inhabit various sites, notably the upper respiratory tract. However, some species of which Streptococcus pyogenes is the most important and are highly pathogenic. The name Streptococcus is derived from Greek word ‘Streptos’ which means twisted or coiled.

Morphology

  • They are Gram positive, spherical or oval cocci and arranged in chains (0.6µm-1µm)
  • They are non – motile, non – sporing. Some strains are capsulated (Figure 7.4).

Streptococcus pyogenes (Flesh eating Bacteria) img 1

Cultural Characteristics

  • They are aerobe and facultative anaerobe. Optimum temperature is 37°C and pH is 7.4 to 7.6
  • They grow only in media enriched with blood or serum. It is cultivated on blood agar. On blood agar, the colonies are small, circular, semitransparent, low convex, with an area of clear hemolysis around colonies (Figure 7.5).
  • Crystal violet blood agar – a selective medium for Streptococcus pyogenes.

Streptococcus pyogenes (Flesh eating Bacteria) img 2

Antigenic Structure

Capsule:

It inhibits phagocytosis

Cell wall:

The outer layer of cell wall consists of protein and lipoteichoic acid which helps in attachment to the host cell. Middle layer of cell wall consists of Group Specific C – Carbohydrate that is used for Lancefield grouping. Inner layer of cell wall is made up of peptidoglycan which has pyrogenic and thrombolytic activity.

Toxins and Enzymes:

Streptococcus pyogenes produces several exotoxins and enzymes which contribute to its virulence.

Toxins and Hemolysins:

Streptococci produces two types of hemolysins which are Streptolysin O and Streptolysin S.

Erythrogenic toxin: (Pyrogenic exotoxin)

The induction of fever is the primary effect of this toxin and it is responsible for the rash of scarlet fever.

Enzymes:

The various enzyme of Streptococcus pyogenes which exhibits virulence activity are listed in Table 7.3.

Enzymes of Streptococcus pyogens and its virulence nature

Enzymes

Virulence nature
Streptokinase (fibrinolysin) It promotes the lysis of human fibrin clot by catalyzing the conversion of plasminogen into plasmin. It facilitates the spread of infection by breaking down the fibrin barrier around the lesions.
Deoxyribonucleases It liquefy the highly viscous DNA that accumulate in thick pusand responsible for thin serous character of streptococcal exudates
Hyaluronidase It breaks down hyaluronic acid of the tissues and favours spread of streptococcal lesion along intercellular spaces.
Other enzymes NADase, lipase, amylase, esterase, phosphates and other enzymes.

Pathogenesis

Streptococcus pyogenes is intrinsically a much more dangerous pathogen than Staphylococcus aureus and has a much greater tendency to spread in the tissues.

Mode of transmission:

Streptococcal infections are transmitted by the following ways:
Streptococcus pyogenes (Flesh eating Bacteria) img 3

Streptococcal diseases may be broadly classified, and it is shown in flowchart 7.1
Streptococcus pyogenes (Flesh eating Bacteria) img 4

Suppurative Infections

1. Respiratory tract infection

a. Streptococcal sore throat:

Sore throat (acute tonsillitis and pharyngitis) is the most common streptococcal diseases. Tonsillitis is more common in older children and adults. The pathogen may spread from throat to the surrounding tissues leading to suppurative (pus – formation) complication such as cervical adenitis (inflammation of a lymph node in the neck) otitis media (inflammation of middle ear), quinsy (ulcers of tonsils) Ludwig’s angina (purulent inflammation around the sub maxillary glands) mastoiditis (inflammation of mastoid process).

b. Scarlet fever:

The disease consists of combination of sore throat and a generalized erythematous (redness of skin or mucous membranes) rash.

2. Skin infections

a. Erysipeals:

It is an acute spreading lesion. The skin shows massive brawny oedema with erythema it is seen in elderly persons or elders.

b. Impetigo: (Streptococcal pyoderma)

It is a skin infection that occurs most often in young children. It consists of superficial blisters that break down and eroded areas whose surface is covered with pus. It is the main cause leading to acute glomerulonephritis in children.

c. Necrotizing fasciitis:

It is an invasive, infection characterized by inflammation and necrosis of the skin, subcutaneous fat and fascia. It is a life-threatening infection.

3. Streptococcal toxic shock syndrome

Streptococcal pyrogenic exotoxin leads to streptococcal toxic shock syndrome (TSS). It is a condition in which the entire organ system collapses, leading to death.

4. Genital infections

Streptococcus pyogenes is an important cause of puerperal sepsis or child bed fever (infection occur when bacteria infect the uterus following child birth)

5. Deep infection

Streptococcus pyogenes may cause pyaemia (blood poisoning characterized by pus forming pathogens in the blood) septicemia (A condition in which bacteria circulate and actively multiply in the bloodstream) abscess in internal organs such as brain, lung, liver and kidney.

Non – Suppurative Complication

Streptococcus pyogenes infections are sometimes followed by two important non – suppurative complications which are, acute rheumatic fever and acute glomerulonephritis. These complications occur 1-4 weeks after the acute infection and it is believed to be the result of hypersensitivity to some streptococcal
components.

1. Rheumatic fever

It is often preceded by sore throat and most serious complication of haemolytic streptococcal infection. The mechanism by which Streptococci produce rheumatic fever is still not clear. A common cross – reacting antigen exist in some group A streptococci and heart, therefore, antibodies produced in response to the streptococcal infection could cross react with myocardial and heart valve tissue, causing cellular destruction.

2. Acute glomerulonephritis

It is often preceded by the skin infection. It is caused by only a few “nephritogenic types (strains)”. It develops because some components of glomerular basement membrane are antigenically similar to the cell membranes of nephritogenic streptococci.

The antibodies Formed against Streptococci cross react with glomerular basement membrane and damage. Some patients develop chronic glomerulonephritis with ultimate kidney failure.

Laboratory Diagnosis

Specimens:

Clinical specimens are collected according to the site of lesion. Throat swab, pus or blood is obtained for culture and serum for serology.

Direct Microscopy:

Gram stained smears of clinical specimens is done, where Gram positive cocci in chains were observed. It is indicative of streptococcal infection.

Culture:

The clinical specimen is inoculated on blood agar medium and incubated at 37° C for 18-24 hours. After incubation period, blood agar medium was observed for zone of beta – haemolysis around colonies.

Catalase test:

Streptococci are catalase negative which is an important test to differentiate Streptococci from Staphylococci.

Serology:

Serological tests are done for rheumatic fever and glomerulonephritis. It is established by demonstrating high levels of antibody to streptococci toxins. The standard test is antistreptolysin Otitration. ASOtitres higher than 200 units are indicative of prior Streptococcal infection.

Treatment and Prophylaxis

  • Penicillin G is the drug of choice.
  • In patients allergic to penicillin, erythromycin or cephalexin is used.
  • Antibiotics have no effect on established glomerulonephritis and rheumatic fever.
  • Prophylaxis is indicated only in the prevention of rheumatic fever, it prevents streptococcal reinjection and further damage to the heart.
  • Penicillin is given for a long period in children who have developed early signs of rheumatic fever.