Acids, Bases and Salts Class 10 Extra Questions with Answers Science Chapter 2

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Class 10 Science Chapter 2 Extra Questions and Answers Acids, Bases and Salts

Extra Questions for Class 10 Science Chapter 2 Acids, Bases and Salts with Answers Solutions

Extra Questions for Class 10 Science Chapter 2 Very Short Answer Type

Class 10 Science Chapter 2 Extra Questions Question 1.
Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid indicating the physical state of the reactants and products.   [Foreign 2010]
Answer:
Na₂CO₃ (s) + 2HCl (ag) → 2NaCl (aq) + CO₂ (g) + H₂O (l)

Acids Bases And Salts Class 10 Extra Questions Question 2.
During summer season, a milkman usually adds a small amount of baking soda to fresh milk. Give reason.   [CBSE Sample Paper 2009]
Answer:
A milkman adds a very small amount of baking soda so as to prevent spoilage of milk. It leads to change in the pH which does not allow bacteria and enzymes to act and milk does not become sour due to fermentation.

Acid Bases And Salts Class 10 Extra Questions Question 3.
What is the difference between slaked lime and lime water?  [CBSE 2010]
Answer:
A suspension of Ca(OH)₂ in water is called slaked lime. Water containing traces of Ca(OH)₂ is called lime water.

Chapter 2 Science Class 10 Extra Questions Question 4.
Which acid is present in sour milk or curd?
Answer:
Lactic acid.

Acids Bases And Salts Extra Questions Question 5.
Why is potassium iodide added into common salt to use it as table salt?
Answer:
The iodide present in the salt prevents thyroid disorders.

Extra Questions For Class 10 Science Chapter 2 Question 6.
What are the pH values of distilled water and common salt solution?  [CBSE 2010]
Answer:
Both are neutral and have pH close to 7.

Ch 2 Science Class 10 Extra Questions Question 7.
A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by-product of chloralkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.  [NCERT Exemplar]
Answer:
Dry pellets of sodium hydroxide absorb moisture and turn sticky when kept in open which is also a by-product of chloralkali process.

When sodium hydroxide is treated with an acidic oxide it produces salt and water.

Acid Bases And Salts Extra Questions Question 8.
Which bases are called alkalies? Give an example of an alkali. [CBSE 2009, 2010]
Answer:
Soluble bases are called alkalies. For example, sodium hydroxide (NaOH).

Class 10 Chemistry Chapter 2 Extra Questions Question 9.
A knife, which is used to cut a fruit, was immediately dipped into water containing drops of blue litmus solution. If the colour of the solution is changed to red, what inference can be drawn about the nature of the fruit and why? [CBSE 2011]
Answer:
Since the colour of the blue litmus has changed to red, this means that the fruit juice is acidic in nature.

Acid Base And Salt Extra Question Answer Question 10.
How do H⁺ ions exist in water?
Answer:
H⁺ ions in water combine with water (H₂O) molecules and exist as H₃O⁺ ion, called hydronium ion.

Class 10 Science Ch 2 Extra Questions Question 11.
What should be done as remedy if stung by leaves of nettle plant in the wild?
Answer:
The area should be rubbed with the leaf of dock plant.

Extra Questions Of Acids Bases And Salts Class 10 Question 12.
What happens when nitric acid is added to egg shell?  [NCERT Exemplar]
Answer:
Egg shell is made of calcium carbonate. When nitric acid is added to egg shell calcium nitrate, carbon dioxide and water are formed.
CaCO₃ + 2HNO₃ → Ca(NO₃)₂ + CO₂ + H₂O

Acid Base And Salts Class 10 Extra Questions Question 13.
What is the concentration of H⁺ ion in pure water?
Answer:
10^-7

Ncert Class 10 Science Chapter 2 Extra Questions Question 14.
Which one of these has a higher concentration of H⁺ ions? 1 M HCl or 1 M CH₃COOH.   [CBSE 2009]
Answer:
1 M HCl has higher concentration of H⁺ ions.

Class 10 Chapter 2 Science Extra Questions Question 15.
Name an example of olfactory indicators.
Answer:
Vanilla.

Question 16.
Name the chemical substance present in thick white and yellowish clouds present in the atmosphere of Venus.
Answer:
Sulphuric acid.

Question 17.
What is acid rain?
Answer:
Rainwater having pH less than 5.6, is called acid rain.

Question 18.
Name the hardest substance in the body.
Answer:
Tooth enamel (Calcium phosphate).

Question 19.
The pH of three solutions A, B and C are 4, 9 and 6 respectively. Arrange them in increasing order of acidic strength. [CBSE 2010]
Answer:
The increasing order of acidic strength is : B < C < A.

Question 20.
Name the chemist who had given the pH scale.
Answer:
S.P.L. Sorensen (1909).

Question 21.
Name the acid present in tomato.
Answer:
Oxalic acid.

Question 22.
Acidic and basic solutions in water conduct electricity. Why?
Answer:
Because they produce hydrogen and hydroxide ions respectively.

Question 23.
What would be the colour of litmus in a solution of sodium carbonate?   [CBSE 2009]
Answer:
Red litmus will change to blue in sodium carbonate solution.

Question 24.
The pH of a sample of vegetable soup was found to be 6.5. How is this soup likely to taste?
Answer:
The taste will be slightly sour as it is weakly acidic.

Question 25.
Name the chemical substance which is used in the manufacture of soap as well as used as a preservative in pickles.
Answer:
Sodium chloride (NaCl).

Question 26.
There are two jars A and B containing food materials. Food in jar ‘A’ is pickled with acetic acid while ‘B’ is not. Food of which of jar will stale first? Explain. Name two synthetic indicators which are used to test acids and bases.
Answer:
Food in jar ‘B’ will stale first because it will undergo oxidation and will also be attacked by microorganisms.
Synthetic indicators: Phenolphthalein, methyl orange.

Question 27.
What is the chemical formula of soda ash?
Answer:
Na₂CO₃

Question 28.
Name the substance used for disinfecting drinking water supply.
Answer:
Bleaching powder.

Question 29.
Name a chemical substance which can be used to detect the presence of moisture in a liquid.
Answer:
Anhydrous copper sulphate.

Question 30.
What is meant by water of crystallisation?
Answer:
Water of crystallisation is the fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form.

Question 31.
Which one is a stronger acid, with pH = 5 or with pH = 2?
Answer:
The acid with pH = 2 is a stronger acid.

Question 32.
Fresh milk has a pH of 6. When it changes into curd (yogurt), will its pH value increases or decrease? Why?
Answer:
Its pH will decrease because curd (yogurt) is sour in taste due to presence of acid in it.

Extra Questions for Class 10 Science Chapter 2 Short Answer Type I

Question 1.
How would you distinguish between baking powder and washing soda by heating?   [NCERT Exemplar]
Answer:
Baking soda (NaHCO₃) gives carbon dioxide and water vapour on heating at very low temperature. The gas so formed turns lime water milky, which confirms the presence of carbon dioxide gas.

When washing soda (Na₂CO₃) is heated it does not produce carbon dioxide even at high temperatures, but gives off its water of crystallisation to become anhydrous salt.

Question 2.
A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in the open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and why does it show such a behaviour? Give the reaction involved.   [NCERT Exemplar]
Answer:
Calcium belongs to group 2. Calcium sulphate is a white soft substance. It is known as Plaster of Paris, which can be moulded into different shapes by making its dough.

When Plaster of Paris is left for some time in the open, it turns into a solid mass because of reaction with moisture present in the atmosphere. The solid mass so formed is known as gypsum and cannot be further used for moulding.

The above said group 2 element is calcium sulpahte.

Question 3.
Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.   [NCERT Exemplar]
Answer:
The acid present in ant sting: Methanoic acid
Chemical Formula of methanoic acid: HCOOH
Method to get relief from the discomfort caused by the ant sting: Rubbing baking soda over the area of ant sting.
Explanation: Rubbing baking soda (a base) over ant sting neutralises the methanoic acid present in the ant sting and gives relief from pain.

Question 4.
List two differences between acids and bases on the basis of chemical properties.
Answer:
(i) Dilute acids like HCl and H₂SO₄ evolve H₂ gas on reacting with metals like Zn, Mg and Ca, etc. and dilute bases do not evolve hydrogen gas.
(ii) Acids react with oxides of metals while bases react with oxides of non-metals.

Question 5.
List four main differences between acids and bases.
Answer:

Properties	Acids	Bases
1. Taste	Sour	Bitter
2. Action on litmus paper	They turn blue litmus paper red	They turn red litmus paper blue.
3. Action with phenolphthalein	No action	They turn phenolphthalein pink.
4. Action with carbonates and bicarbonates	They decompose carbonates and bicarbonates to liberate carbon dioxide.	No action

Question 6.
Mention the terms defined by the following sentences:
(a) A soluble base
(b) The insoluble solid formed when two solution are mixed together.
Answer:
(a) Alkali
(b) Precipitate.

Question 7.
Name the product formed in each case when:
(а) hydrochloric acid reacts with caustic soda.
(b) granulated zinc reacts with caustic soda.
Answer:
(a) The product formed is a mixture of sodium chloride and water.
NaOH (ag) + HCl (ag) → NaCl (ag) + H₂O

(b) The product formed is a mixture of sodium zincate and hydrogen gas.
Zn (s) + 2NaOH (ag) → Na₂ZnO₂ (ag) + H₂(g)

Question 8.
Explain why sodium hydroxide solution cannot be kept in aluminium containers? Write equation for the reaction that may take place for the same.
Answer:
Sodium hydroxide solution reacts with aluminium to form sodium metaaluminate and hydrogen is evolved. Therefore, it cannot be kept in a container made of aluminium.

Question 9.
How can you obtain the following gases by using dilute acid and one other substance?
(а) hydrogen
(b) carbon dioxide.
Answer:
(a) Fe + H₂SO₄(dil.) → FeSO₄ + H₂(g)
Mg + 2HCl(dil.) → MgCl₂ + H₂(g)

(b) Na₂CO₃ + 2HCl(dil.) → 2NaCl + H₂O + CO₂(g)
NaHCO₃ + HCl(dil.) → NaCl + H₂O + CO₂(g)

Question 10.
A solution of HCl is taken in a beaker and an electric circuit with a bulb is set up with the solution in series. What happens to the bulb and why?
Answer:
The bulb will start glowing. Glowing of the bulb indicates that there is a flow of electric current through the solution. Electric current is carried through the solution by ions.

Since the cation present in acids is H⁺, this suggests that acids produce hydrogen ions, H⁺(ag), in solution, which are responsible for carrying current through the solution.

Question 11.
If 280 g of washing soda crystals are left in dry air for some time, a loss of weight of 162 g occurs. How can you account for this?
Answer:
Washing soda (Na₂CO₃. 10H₂O) is an efflorescent substance (if exposed to air, it loses most of its water of crystallisation). 280 g of washing soda lose 162 g of its water of crystallisation.

Question 12.
A sample of bleaching powder was kept in an air tight container. After a month, it lost some of its chlorine content. How will you account for it?
Answer:
Bleaching powder if kept even in an air tight container, will slowly decompose on its own and form calcium chlorate and calcium chloride. The reaction is called auto oxidation. This will result in decrease in its chlorine contents.

Question 13.
A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water. Identify the compound. Write chemical equation to prepare the compound. Mention one important use of the compound.
Answer:
The compound is Plaster of Paris (CaSO₄. \(\frac { 1 }{ 2 }\) H₂O). It is formed from gypsum (CaSO₄ . \(\frac { 1 }{ 2 }\) H₂O) upon heating to a temperature of 373 K. It changes back to gypsum on adding water. Plaster of Paris is used for setting fractured bones.

Question 14.
A white powder is added while baking breads and cakes to make them soft and fluffy. Write the name of the powder. Name its main ingredients. Explain the function of each ingredient. Write the chemical reaction taking place when the powder is heated during baking.   [CBSE 2012, 2013]
Answer:
The white powder is known as baking powder. The main ingredients are baking soda (NaHCO₃) and tartaric acid (C₄H₆O₆).

Question 15.
Explain giving reasons:
(i) Tartaric acid is a component of baking powder used in making cakes.
(ii) Gypsum (CaSO₄. 2H₂O) is used in the manufacture of cement.
Answer:
(i) Role of tartaric acid in baking powder (mixture of tartaric acid and sodium hydrogencarbonate) is to neutralise sodium carbonate formed upon heating sodium hydrogencarbonate.

In case it is not done, cake will be better and sodium carbonate will also have injurious side effects.

(ii) The role of gypsum (CaSO₄.2H₂O) in the manufacture of cement is to slow down the process of setting of cement.

Extra Questions for Class 10 Science Chapter 2 Short Answer Type II

Question 1.
What will be the action of the following substances on litmus paper?
Dry HCl gas, moistened NH₃ gas, lemon juice, carbonated soft drink, curd, soap solution.  [NCERT Exemplar]
Answer:
Dry HCl gas: No action
Moistened NH₃ gas: Turns red litmus blue.
Lemon juice: Turns blue litmus red.
Carbonated soft drink: Turns blue litmus red.
Curd: Turns blue litmus red.
Soap solution: Turns red litmus blue.

Explanation:

• Dry HCl gas does not liberate hydrogen ion, hence no action takes place with litmus paper.
• NH₃ gas forms ammonium hydroxide with water which turns red litmus paper blue.
• Lemon juice is citric acid, so it turns blue litmus paper red.
• Carbonate soft drink contains carbon dioxide dissolved in water. Carbon dioxide forms carbonic acid with water; which turns blue litmus paper red.
• Curd contains lactic acid and hence turns blue litmus paper red.
• Soap solution is basic in nature hence it turns red litmus paper blue.

Question 2.
When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.   [NCERT Exemplar]
Answer:
Zinc metal gives hydrogen gas when it is treated with dilute sulphuric acid. Hydrogen gas is utilised in hydrogenation of oil.
Therefore, the gas evolved is hydrogen.

Test for hydrogen gas: When a burning candle is brought near hydrogen gas, it bums with a pop sound which confirms the presence of hydrogen gas.

Question 3.
(i) Identify the compound of calcium which is a yellowish powder and is used for disinfecting drinking water. Write its chemical name and formulae.
(ii) Write the balanced chemical equation of chlor-alkali process.   [CBSE 2012, 2014]
Answer:
(i) The yellowish white solid is known as bleaching powder. Chemically, it is calcium oxychloride or calcium hypochlorite. Its chemical formula is CaOCl₂.

(ii) Chemical equation for chlor-alkali process is

Question 4.
Explain with suitable reason
(a) Ferric chloride is stored in air tight bottles.
(b) On exposure to atmosphere, Glaublar’s salt loses weight while quicklime gains weight.
(c) Common salt (containing traces of magnesium chloride) becomes sticky during the monsoons.
Answer:
(a) Because ferric chloride is deliquescent in nature.
(b) Glaubar’s salt is efflorescent and loses water of crystallisation whereas quick lime is hygroscopic in nature and absorbs moisture from the air.
(c) This is because magnesium chloride is deliquescent and absorbs moisture from the atmospheric air and becomes moist.

Question 5.
(a) A solution has a pH of 7. Explain how you would
(i) increases its pH
(ii) decrease its pH
(b) If a solution changes the colour of litmus from red to blue, what can you say about its pH?
(c) What can you say about the pH of a solution that liberates CO₂ from sodium carbonate?
Answer:
(a) (i) By adding some alkali like NaOH
(ii) By adding some acid like HCl

(b) Since the solution changes the colour of litmus from red to blue it is alkaline and hence it has pH > 7.

(c) Since the solution liberates CO₂ from sodium carbonate, it should be acidic and has pH < 7.

Question 6.
A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water.
(i) Identify the compound.
(ii) Write the chemical equation for its preparation.
(iii) Mention one important use of this compound.
Answer:
(i) Plaster of Paris

(iii) It is used for plastering fractured bones.

Question 7.
Write any three chemical properties of acids.
Answer:
(i) They react with metals to give out hydrogen gas, for example,

(ii) They react with bases to form salt and water, for example,

(iii) They react with metal carbonates to liberate carbon dioxide gas.

Question 8.
Classify the solutions of the following as acids, bases and salts:
Ammonium hydroxide, barium chloride, sodium chloride, sodium hydroxide, sulphuric acid and nitric acid.
Answer:

Acids	Bases	Salts
1. Sulphuric acid	Ammonium hydroxide	Barium chloride
2. Nitric acid	Sodium hydroxide	Sodium chloride

Question 9.
You are given two solutions A and B. The pH of solution A is 6 and pH of solution B is 8.
(i) Which solution is acidic and which is basic?
(ii) Which solution has more H+ ion concentration?
(iii) Why is HCl a stronger acid than acetic acid?   [CBSE 2011]
Answer:
(i) The solution with pH 6 is acidic while the solution with pH 8 is basic.
(ii) The solution with pH 6 has more H⁺ ion concentration.
(iii) HCl is a stronger acid than CH₃COOH since its degree of dissociation (α) is more or it releases more H+ ions in solution than acetic acid.

Question 10.
What is tooth enamel chemically? State the conditions when it starts corroding. What happens when food particles left in the mouth after eating degrade? Why do doctors suggest use of powder/tooth paste to prevent tooth decay? [CBSE 20011, 2014]
Answer:
(i) The tooth enamel is chemically calcium phosphate with the formula Ca₃(PO₄)₂. It is quite hard.
(ii) The enamel starts corroding when the pH inside our mouth falls below 5.5 because the saliva present in the mouth becomes acidic.
(iii) The bacteria present in the mouth breakdown the food particles into acids which damage our teeth by corroding them.
(iv) The contents of the tooth paste are of basic nature. They neutralise the excess acid present. As a result, the corrosion of enamel and decay of teeth are checked.

Question 11.
(a) Write the name given to bases that are highly soluble in water. Give an example.
(b) How is tooth decay related to pH? How can it be prevented?
(c) Why does bee sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How?
Answer:
(a) Alkali, for example, NaOH (Sodium hydroxide).

(b) Lower the pH, more will be tooth decay. Acid formed in the mouth reacts with enamel which is made up of [Ca₃(PO₄)₂] and causes tooth decay.
It can be prevented by brushing our teeth after every meal.

(c) A bee injects formic acid into the skin when it stings which causes pain and irritation. Sodium hydrogencarbonate (baking soda) neutralises formic acid giving relief.

Question 12.
Mention the colour changes observed when the following indicators are added to acids:
(i) Alkaline phenolphthalein solution
(ii) Methyl orange solution
(iii) Neutral litmus solution
Answer:
(i) It gets decolourised
(ii) It turns red or pink
(iii) It turns red.

Question 13.
Choosing only substances from the list given in the box below, write equations for the reactions which you would use in the laboratory to obtain:
(a) Sodium sulphate
(b) Iron (II) sulphate
(c) Zinc carbonate.
Dilute sulphuric acid, copper, iron, copper carbonate, sodium, zinc, sodium carbonate
Answer:
(a) Sodium sulphate
Na₂CO₃ + H₂SO₄ (dil.) → Na₂SO₄ + H₂O + CO₂ (g)

(b) Iron (II) sulphate
Pe + H₂SO₄ (dil.) → FeSO₄ + H₂ (g)

(c) Zinc carbonate
Zn + CuCO₃ → ZnCO₃ + Cu

Question 14.
What is dilution? What precaution should be taken during dilution of a strong acid like sulphuric acid?
Answer:
Dilution is a process in which concentration of a substance decreases by addition of a solvent. Care must be taken while mixing concentrated sulphuric acid with water as the process is a highly exothermic one. The acid must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

Question 15.
Write balanced equations to satisfy each statement:
(a) Acid + Chloride → Salt + Hydrochloric acid gas
(b) Acid + Carbonate → Salt + Water + Carbon dioxide
(c) Acid + Sulphite → Salt + Water + Sulphur dioxide
Answer:
(a) H₂SO₄ + NaCl → NaHSO₄ + HCl (g)
(b) 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂ (g)
(c) 2HCl + CaSO₃ → CaCl₂ + H₂O + SO₂ (g)

Extra Questions for Class 10 Science Chapter 2 Long Answer Type

Question 1.
What are strong and weak acids? In the following list of acids, separate strong acids from weak acids.  [NCERT Exemplar]
Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.
Answer:
Strong acid: Strong acids ionise completely in their aqueous solutions to produce a large number of hydrogen ions. Mineral acids are generally strong acids.

Weak acid: Weak acids do not ionise completely in their aqueous solution. Organic acids are generally weak acids.

Strong acid: Hydrochloric acid, nitric acid, sulphuric acid
Weak acid: Citric acid, acetic acid, formic acid

Question 2.
(i) Explain, why is hydrochloric acid a strong acid and acetic acid, a weak acid? How can it be verified?
(ii) Explain, why aqueous solution of an acid conducts electricity?
(iii) You have four solutions A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7.
(a) Identify the most acidic and most basic solutions.
(b) Arrange the above four solutions in the increasing order of H+ ion concentration.
(c) State the change in colour of pH paper on dipping in solution C and D.   [CBSE 2012, 2013]
Answer:
(i) Hydrochloric acid (HCl) is a stronger acid than acetic acid (CH₃COOH) because it dissociates completely into H⁺ and Cl^– ions in aqueous solution. In order to verify this, add a few drops of universal indicator solution in the test tubes containing the acids. It acquires red colour in hydrochloric acid and yellow in acetic acid which confirms that hydrochloric acid is a stronger acid.

(ii) An aqueous solution of an acid releases ions in aqueous solutions. These ions conduct electricity.

(iii) (a) Most acidic is A (pH = 6) and most basic is C (pH = 12).
(b) The increasing order of H⁺ ion concentration is : C < B < D < A.
(c) The pH paper acquires dark purple colour in solution C and green in solution D.

Question 3.
Fill the missing data in the following table:

Answer:

Question 4.
(a) Explain how antacids give relief from acidity. Write the name of one such antacid.
(b) Fresh milk has a pH of 6. How does the pH change as it turns to curd? Explain your answer.
(c) A milkman adds a very small amount of baking soda to fresh milk. Why does this milk take a longer time to set as curd?
(d) Mention the nature of toothpastes. How do they prevent tooth decay?
Answer:
(a) Our stomach produces hydrochloric acid that helps in digestion of food. During indigestion, our stomach produces excess acid. Antacids neutralise the excess of acid produced and gives relief from hyperacidity. Milk of magnesia (magnesium hydroxide) is one of such antacid.

(b) pH will decrease as it turns to curd because curd is acidic due to the presence of lactic acid.

(c) It takes longer time to set as curd as the presence of baking soda (sodium hydrogen carbonate) makes the milk basic and it does not allow it to become acidic easily.

(d) Toothpastes are basic in nature. They neutralise the acid formed in mouth which causes tooth decay.

Question 5.
(a) Explain the following chemical properties of acids with the help of balanced chemical equations only.
(i) when an acid reacts with a metal carbonate
(ii) when an acid reacts with a metal bicarbonate
(iii) when an acid reacts with a metal oxide.
(b) You are given three solutions A, B and C with pH values 2, 10 and 13 respectively. Write which solution has more hydrogen ion concentration among the three and state the nature ‘acidic or basic’ of each solution.
Answer:
(a) (i) CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
(ii) NaHCO₃ + HCl → NaCl + H₂O + CO₂
(iii) Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

(b) ‘A’ has maximum [H₃O⁺] equal 10^-2 mol L^-1
‘A’ acidic whereas B and C are basic in nature.

Question 6.
Complete the following reaction:
(i) 2NaCl (aq) + 2H₂O(l) →
(ii) Ca(OH)₂ + Cl₂ →
(iii) NaCl + H₂O + CO₂ + NH₃ →
(iv)
(v) Na₂CO₃ + 10H₂O
Answer:
(i) 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
(ii) Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Acids Bases and Salts HOTS Questions With Answers

Question 1.
A student prepared solutions of (i) an acid and (ii) a base in two separate beakers. She forgot to label the solutions and litmus paper was not available in the laboratory. Since both the solutions were colourless, how would she distinguish between the two?  [NCERT Exemplar]
Answer:
While answering this question, we need to make certain assumptions. Let us assume that laboratory has all the necessary items but no litmus paper. We can use phenolphthalein to check which of the beakers contains acid and which one contains a base. Apart from that, we can also use other natural indicators; like China rose or turmeric.

Question 2.
Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B and C.  [NCERT Exemplar]
Answer:
Baking powder which is a salt used in bakery products. It give sodium carbonate and carbon dioxide gas on heating. Sodium carbonate is used to remove hardness of water. Carbon dioxide turns lime water milky.

Therefore,

• Salt A, which is sodium bicarbonate and used as baking powder.
• Salt B is sodium carbonate, which is used to remove hardness of water.
• The C is carbon dioxicje gas which turns lime water milky.

Question 3.
In one of the industrial processes used for manufacture of sodium hydroxide, a gas X is formed as by product. The gas X reacts with lime water to give a compound Y which is used as bleaching agent in chemical industry. Identify X and Y giving the chemical equation of the reactions involved.   [NCERT Exemplar]
Answer:
Sodium chloride is used in the manufacture of sodium hydroxide by the Chlor-Alkali process. In this process chlorine and hydrogen gas are formed as by products along with sodium hydroxide. Chlorine gas reacts with lime water to produce bleaching power which is used as bleaching agent in chemical industries.

Therefore,

• The gas ‘X’ is chlorine.
• Compound Y is calcium oxychloride which is commonly known as bleaching powder and used as bleaching agent in chemical industries.

Question 4.
In the following schematic diagram for the preparation of hydrogen gas as shown in Figure. What would happen if following changes are made?   [NCERT Exemplar]
Answer:

(a) In place of zinc granules, same amount of zinc dust is taken in the test tube.
(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
(c) In place of zinc, copper turnings are taken.
(d) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.
Answer:
(a) When zinc dust is taken instead of zinc granules to react with sulphuric acid, hydrogen gas is formed. But the rate of reaction increases in the case of zinc dust compared to zinc granules, because of increased surface area of zinc dust which increases the rate of reaction.

Thus, when zinc dust is used in the place of zinc granules, hydrogen gas is produced at a faster rate.

(b) Zinc granules give hydrogen gas; along with zinc chloride; when they react with hydrochloric acid.

Thus, when hydrochloric acid is used in place of sulphuric acid, zinc chloride is formed instead of zinc sulphate; along with hydrogen gas and the reaction takes place at the same rate.

(c) Copper does not react with dilute acids under normal conditions because copper lies at lower position in the reactivity series and does not displace hydrogen from dilute acids.
Thus, if copper turnings are taken in place of zinc granules, no reaction will take place.

(d) If sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated, sodium zincate is formed along with hydrogen gas. Heating the test tube will increase the rate of formation of hydrogen gas as heating the reaction mixture increases the rate of reaction.

Question 5.
Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.   [NCERT Exemplar]
Answer:

Answer:

Therefore,

• Compound “X’ is sodium hydroxide (NaOH).
• Compound ‘A’ is zinc sulphate (ZnSO₄).
• Compound ‘B’ is sodium chloride (NaCl).
• Compound ‘C’ is sodium acetate (CH₃COONa).

Question 6.
A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at the anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G and Z.   [NCERT Exemplar]
Answer:
Calcium carbonate gives carbon dioxide gas when it reacts with hydrochloric acid.

Carbon dioxide turns lime water milky when passed through it because of formation of calcium carbonate. When carbon dioxide; so formed; is passed through lime water, it turns milky because of the formation of calcium carbonate.

On electrolysis of brine, chlorine gas is produced at the anode. Therefore G is Cl₂.
Bleaching powder is used in disinfecting drinking water.
Therefore Z can be CaOCl₂.
When chlorine is passed through dry calcium hydroxide [Ca(OH)₂], bleaching powder CaOCl₂ is formed.

Therefore, Y is calcium hydroxide, Ca(OH)₂.
Since Y reacts with a gas to give a carbonate, the gas is CO₂ and the carbonate is CaCO₃.

Therefore, the metal carbonate X is calcium carbonate, CaCO₃.
Therefore,

• Metal carbonate ‘X’ is calcium carbonate.
• Solution ‘Y is lime water (Calcium hydroxide).
• Gas ‘G’ is chlorine gas.
• Dry Y’ is dry calcium hydroxide (dry slaked lime).
• Compound ‘Z’ is bleaching powder (Calcium oxychloride).

Question 7.
A substance X used as an antacid reacts with hydrochloric acid to produce a gas Y which is used in extinguishers.
(а) Name the substances X and Y.
(b) Write a balanced equation of the reaction between X and hydrochloric acid.   [CBSE 2011]
Answer:
(a) Substance X is sodium hydrogencarbonate (X) and the gas evolved Y is carbon dioxide.
(b)

Question 8.
You are provided with the following materials in your laboratory:
Answer:
Hydrochloric acid (HCl), sulphuric acid, (H₂SO₄), nitric acid (HNO₃), acetic acid (CH₃COOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide [Ca(OH)₂], magnesium hydroxide [Mg(OH)₃] and ammonium hydroxide (NH₄OH).
If we test each of the above solutions one by one with a drop of the following indicators, what colour change will you observe?
Red litmus, blue litmus, phenophthalein, methyl orange.
Answer:
Acidic substances: HCl, H₂SO₄, HNO₃, CH₃COOH
They will turn blue litmus red and methyl orange red. There will be no effect on red litmus and phenolphthalein.

Basic substances: NaOH, KOH, Ca(OH)₂, Mg(OH)₂, NH₄OH. They will turn red litmus blue and phenolphthalein pink. There will be no effect on blue litmus and methyl orange.

Question 9.
The crystals of a compound A on keeping in air get converted into a white powder. Its solution in water gives blue colour with red litmus. It is used to remove permanent hardness from water.
(a) Identify the substance. Write chemical formula for its crystalline form.
(b) From the given information, identify the nature of the substance.
(c) Write two more uses of the substance.   [CBSE 2013]
Answer:
(a) The substance is washing soda. Its chemical formula is Na₂CO₃.10H₂O.
(b) Since the aqueous solution of the substance in water turns red litmus blue, it is of basic nature.
(c) (i) It is used in laundry for washing clothes.
(ii) It is used in the manufacture of glass, paper and chemicals like caustic soda (NaOH), and borax (Na₂B₄O₇), etc.

Question 10.
A substance X is used as a building material and is insoluble in water. When reacted with dilute HCl, it produces a gas which turns lime water milky. Predict the substance. Write the chemical equations evolved.
Answer:
The substance is probably calcium carbonate (CaCO₃), also called lime stone or marble. It is used as a building material. On reacting with dilute HCl, it evolves CO₂ gas which turns lime water milky.

Question 11.
When electricity is passed through a common salt solution, sodium hydroxide is produced along with the liberation of two gases ‘X’ and T. The gas ‘X’ burns with a pop sound whereas T is used for disinfecting drinking water.  [CBSE 2011]
(i) Identify X and Y.
(ii) Give the chemical equation for the reaction stated above.
(iii) State the reaction of Y with dry slaked lime.
Answer:
(i) The gas X’ is H₂ and gas ‘Y’ is Cl₂.
(ii) The chemical equation for the reaction is:

(iii) Cl₂ reacts with slaked lime to form bleaching powder.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Extra Questions for Class 10 Science Chapter 2 Value Based

Question 1.
Aman is fond of eating fast foods and chat. He was suffering from a stomach pain and indigestion for a number of days. Doctor advised him to take antacid tablet after each meal and avoid spicy and junk food. He followed the advice and was cured rapidly.
(i) What is an antacid?
(ii) How are antacid tablets helpful in such indigestion? Justify by the relevant chemical reaction.
(iii) Mention the values exhibited by Aman and the doctor.
Answer:
(i) Antacid is a substance which can neutralise acidity in the stomach.
(ii) The antacid tablets or gels contain base like NaHCO₃ or Mg(OH)₂ which neutralise the effect of excess HCl released in the stomach as
NaHCO₃ + HCl → NaCl + H₂O + CO₂
(iii) Knowledge of Chemistry, caring.

Question 2.
Ayush has cold drinks, chocolates and sweets every day. His teeth were getting damaged. His science teacher asked him to brush his teeth after every meal as well as after eating sweets.
(i) How do the teeth get damaged due to eating chocolates and sweets?
(ii) Brushing of teeth is helpful and prevent tooth decay. Justify.
(iii) Mention the values exhibited by the science teacher.
Answer:
(i) On eating sweets/chocolates the pH of mouth becomes less than 5.5, so tooth enamel gets corroded and tooth decay starts.
(ii) Using toothpaste, which is basic in nature can neutralise the excess acid formed in the mouth and prevent tooth decay.
(iii) Caring, helpful nature, knowledge of Chemistry.

Question 3.
Mohan and Priyanka were playing in the garden. Priyanka was stung by a bee and started crying and returned home. Her mother immediately observed the affected area and applied a thin coating of toothpaste as first aid, then took her to the nearest doctor.
(i) Why did Priyanka cry?
(ii) Name the chemical substance present in bee sting.
(iii) How is toothpaste effective in such incident?
(iv) Mention the values exhibited by Priyanka’s mother.
Answer:
(i) Priyanka cried because the bee injected an acid while stinging which caused pain and irritation.
(ii) Formic acid or Methanoic acid (HCOOH)
(iii) Toothpaste is basic in nature so it neutralise the effect of formic acid and gives relief.
(iv) Knowledge of Chemistry, caring nature.

Question 4.
Manshi is a student of class X in a city school. There was a tall tree at the edge of the garden having a large honeycomb attached to it. Some students were playing cricket in the school playground. Suddenly the cricket ball hit the honeycomb due to which a large number of honey-bees started flying here and there. Manshi was stung on her face by a honey-bee. The sting was so painful that Manshi started crying. One of her classmates Shanti quickly got some baking soda and made a paste of it with water. Then she applied the paste on the stung area of the face. On rubbing baking soda solution, Manshi felt a lot of relief from the pain.
(a) What kind of liquid is injected into the skin when honey-bee strings?
(b) Why did rubbing baking soda solution on the stung area of skin give relief from pain?
(c) What type of chemical reaction takes place when baking soda solution is rubbed on the area stung by honey-bee?
(d) What values are exhibited by Shanti and the classmates?
Answer:
(а) Honey-bee sting injects an acidic liquid into the skin.

(b) Baking soda is a mild base. Being a base, baking soda solution neutralises the acidic liquid injected by honey-bee sting and neutralises its effect. This gives relief from pain.

(c) Neutralisation reaction (between an acid and a base)

(d) The values displayed by Shanti and classmates are

• Awareness
• Knowledge of Chemistry and
• Desire to remove the suffering of others.