SCIENCE | Class 10; Question Bank Solutions; Chapter 2: Acids, Bases and Salts

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Chapter: 2 – ACIDS, BASES AND SALTS
HSLC Exam. Questions
A. MCQ & Very Short Questions: Mark: 1

(i) A solution reacts with crushed egg-shells to give a gas that turns lime water milky. The solution contains – [HSLC’15, ’19]
Answer: (b) HCl

Options:
(a) NaCl
(b) HCl ✅
(c) LiCl
(d) KCl

(ii) A solution turns red litmus blue. The pH of the solution is – [HSLC’16, 18, 22]
Answer: (c) 9

Options:
(a) 1
(b) 4
(c) 9 ✅
(d) 10

(iii) Which one of the following types of medicines is used for treating indigestion? [HSLC’17]
Answer: (c) Antacid

Options:
(a) Antibiotic
(b) Analgesic
(c) Antacid ✅
(d) Antiseptic

(iv) Which of the following compounds is used in soda-acid fire extinguisher? [HSLC’23]
Answer: (b) Na₂CO₃

Options:
(a) NaCl
(b) Na₂CO₃ ✅
(c) NaHCO₃
(d) NH₄Cl

(v) Which one of the following is olfactory indicator? [HSLC’24]
Answer: (c) Vanilla

Options:
(a) Litmus
(b) Turmeric
(c) Vanilla ✅
(d) Phenolphthalein

(vi) Consider the following statements regarding tooth decay:
(i) Tooth decay starts at a pH lower than 5.5.
(ii) Tooth decay is caused by phosphoric acid which lowers pH.
Which among the following options is correct? [HSLC’24]
Answer: (a) (i) is true and (ii) is false

Options:
(a) (i) is true and (ii) is false ✅
(b) (i) is false and (ii) is true
(c) Both (i) and (ii) are true
(d) Both (i) and (ii) are false

(vii) Which of the following compounds is used in soda-acid fire extinguisher? [HSLC’25]
Answer: (b) Na₂CO₃

Options:
(a) NH₄Cl
(b) Na₂CO₃ ✅
(c) NaCl
(d) NaHCO₃

(viii) The pH of a neutral solution is – [HSLC’25]
Answer: (a) 7

Options:
(a) 7 ✅
(b) 6
(c) 5
(d) 8

(ix) How is sodium carbonate obtained from baking soda? [HSLC’25]
Answer: (a) By heating baking soda

Options:
(a) By heating baking soda ✅
(b) By adding water to baking soda
(c) By reacting baking soda with acid
(d) By reacting baking soda with base

2. Determine true or false:
Statement: Non-metals can displace hydrogen from dilute acids.
Answer: False
👉 Non-metals generally do not displace hydrogen from dilute acids because they do not release electrons to reduce hydrogen ions.

3. How is the life of the filament of an electric bulb prolonged? [HSLC’17]
Answer:
The life of the filament of an electric bulb is prolonged by filling the bulb with inert gases such as argon or nitrogen. These gases prevent the filament from oxidizing and reduce its evaporation.

4. Food cans are coated with tin and not with zinc because – [HSLC’18]
Answer: (c) Zinc is more reactive than tin. ✅
👉 If zinc is used, it will react with the acids present in food, leading to contamination. Tin, being less reactive, is safer for coating.

Options:
(a) Zinc is costlier than tin
(b) Zinc has a higher melting point than tin
(c) Zinc is more reactive than tin ✅
(d) Zinc is less reactive than tin

5. Write a chemical equation to show the reaction between Plaster of Paris and Water. [HSLC’17]

(Plaster of Paris + Water → Gypsum)

6. What is the common name of the compound CaOCl₂? [HSLC’18]
Answer: Bleaching Powder

B. Short Type Questions

1. What is pH? You are given two solutions A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these solutions is acidic and which one is basic?

[HSLC’15]

Answer:
The pH is a scale used to measure the concentration of hydrogen ions (H⁺) in a solution. The scale ranges from 0 to 14.

A pH less than 7 indicates an acidic solution.
A pH more than 7 indicates a basic solution.
A pH equal to 7 indicates a neutral solution.

Since solution A has pH = 6 and solution B has pH = 8:

Solution A is acidic and has more hydrogen ion concentration.
Solution B is basic.

2. What is Plaster of Paris? How is it prepared? Give one important use.

[HSLC’15]

Answer:
Plaster of Paris (POP) is a white powdery substance with the chemical formula CaSO₄·½H₂O.

It is prepared by heating gypsum (CaSO₄·2H₂O) at 373 K.
Equation:

Important use: POP is used for making moulds, surgical casts, and decorative items.

3. Name the Sodium compound which is used for softening hard water.

[HSLC’16]

Answer:
The sodium compound used for softening hard water is Sodium carbonate.
Chemical formula: Na₂CO₃
It reacts with calcium and magnesium salts (which cause hardness) to form insoluble compounds that can be removed.

4. You are given two solutions A and B. The pH of solution A is 3 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these solutions is acidic and which one is basic?

[HSLC’17]

Answer:

Solution A (pH = 3) is acidic and has more hydrogen ion concentration.
Solution B (pH = 8) is basic and has lower H⁺ concentration.
pH and hydrogen ion concentration are inversely related.

5. What is the chemical name of baking soda? How is it produced? Give chemical equation.

[HSLC’18]

Answer:

Chemical name: Sodium hydrogen carbonate or Sodium bicarbonate
Chemical formula: NaHCO₃

Preparation reaction (Solvay process):

6. What is a neutralization reaction? Give two examples.

[HSLC’19]

Answer:
A neutralization reaction is a chemical reaction in which an acid reacts with a base to form salt and water.

General reaction: Acid+Base = Salt+ water

Examples:

HCl + NaOH → NaCl + H₂O
H₂SO₄ + KOH → K₂SO₄ + H₂O

7. You have been provided with three test tubes. One contains distilled water, another contains an acidic solution, and the third a basic solution. Using only red litmus paper, how will you identify each?

[HSLC’19]

Answer:
Use red litmus paper for testing:

In acidic solution: red litmus → remains red
In basic solution: red litmus → turns blue
In distilled water (neutral): red litmus → remains red

✅ [HSLC]

8. You have two solutions, A and B. The pH of solution A is 6 and that of B is 8. Which solution has more hydrogen ion concentration? Which is acidic and which is basic?

[HSLC’20]

Answer:

Solution A (pH 6) has more hydrogen ions and is acidic.
Solution B (pH 8) has fewer H⁺ ions and is basic.
As pH decreases, acidity and hydrogen ion concentration increase.

✅ [HSLC]

9. Reaction of copper oxide and hydrochloric acid – answer the following:

[HSLC’20]

(i) Colour of solution: Blue
(ii) What happened to CuO: It reacts with HCl to form copper chloride (CuCl₂) and water.
(iii) Balanced chemical equation:

10. What is brine? What is the product formed when electricity is passed through this brine? Write balanced chemical equation.

[HSLC’20]

Answer:

Brine is a concentrated solution of sodium chloride (NaCl) in water.
Electrolysis of brine produces:
- Chlorine gas (Cl₂) at the anode
- Hydrogen gas (H₂) at the cathode
- Sodium hydroxide (NaOH) in the solution

Balanced equation:

11. What are oxidation and reduction reactions? Explain with examples.

[HSLC’22]

Answer:

Oxidation: Gain of oxygen or loss of electrons/hydrogen.
Reduction: Loss of oxygen or gain of electrons/hydrogen.

Example:

H₂ is oxidized (gains oxygen)

13. Explain why does an aqueous solution of an acid conduct electricity.

[HSLC’22]

Answer:
An aqueous solution of an acid conducts electricity because acids ionize in water to release hydrogen ions (H⁺) or hydronium ions (H₃O⁺). These free ions are charged particles that can carry electric current through the solution.

For example: HCl= H+ + Cl-

The presence of these ions allows the solution to conduct electricity.

14. What is acid rain? How does it affect our aquatic life?

[HSLC’22]

Answer:
Acid rain is rainwater that has become acidic due to the presence of sulphur dioxide (SO₂) and nitrogen oxides (NO₂) dissolved in it. These gases mix with water vapour in the atmosphere to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃).

Effect on aquatic life:

Acid rain lowers the pH of lakes and rivers, making the water acidic.
Aquatic organisms like fish and amphibians cannot survive in low pH, leading to death and decline in biodiversity.

15. Write one method for the preparation of bleaching powder. Write two uses of it.

[HSLC’23]

Answer:
Preparation of bleaching powder:
Bleaching powder is prepared by reacting chlorine gas with dry slaked lime (Ca(OH)₂)

Uses of bleaching powder:

Used for disinfecting drinking water.
Used as a bleaching agent in the textile and paper industries.

16. Find the product of the following reactions:

[HSLC’23]

17. How is the concentration of (a) hydronium ions (H₃O⁺) affected when an acid is diluted and (b) hydroxide ions (OH⁻) affected when excess base is dissolved in sodium hydroxide solution?

[HSLC’25]

Answer:

(a) When an acid is diluted (more water is added), the concentration of hydronium ions (H₃O⁺) decreases. This is because the H⁺ ions become more spread out in the solution.

(b) When excess base is added to a sodium hydroxide solution, the concentration of hydroxide ions (OH⁻) increases, making the solution more basic.

18. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain.

[HSLC’25]

Answer:
As milk turns into curd, it undergoes a fermentation process in which lactic acid is produced by bacteria. This increases the acidity of the solution.

Hence, the pH decreases from 6 to below 6, making curd more acidic than fresh milk.

19. What is a neutralization reaction? Give two examples.

[HSLC’25]

Answer:
A neutralization reaction is a chemical reaction in which an acid reacts with a base to form salt and water.

General form: Acid+ Base= Salt+ water

Examples:

HCl + NaOH → NaCl + H₂O
H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O

🔶 Assertion & Reasoning Questions

(1)

Assertion (A): When acid reacts with base, salt and water are produced.
Reason (R): When salt reacts with water, acid and base are produced.

✅ Answer: (c) – (A) is true but (R) is false

Explanation:

The assertion is correct. This is the definition of a neutralization reaction.

HCl + NaOH → NaCl + H₂O

The reason is incorrect. When salt dissolves in water, it does not produce acid and base again. Most salts simply dissolve and dissociate into ions, but do not reverse the neutralization.

(2)

Assertion (A): The taste of acid is sour and the taste of base is basic.
Reason (R): Sometimes the taste of both acid and base may be similar.

✅ Answer: (c) – (A) is true but (R) is false

Explanation:

The assertion is correct.
- Acids (like lemon juice or vinegar) taste sour.
- Bases (like baking soda) taste bitter and are soapy.
The reason is incorrect. The taste of acids and bases are never similar. Acids are always sour, and bases are bitter – this is a basic property of these substances.

(3)

Assertion (A): Limestones, chalks, and marbles are three forms of calcium carbonate.
Reason (R): All metal carbonates produce salt, carbon dioxide, and water if they react with acids.

✅ Answer: (a) – Both (A) and (R) are true and (R) is the correct explanation of (A)

Explanation:

The assertion is true.
- Limestone, chalk, and marble are all natural forms of Calcium Carbonate (CaCO₃).
The reason is also true, and it explains the assertion well.
- All metal carbonates react with acids to produce salt + CO₂ + H₂O.

(4)

Assertion (A): The characteristics of all non-metal oxides are acidic.
Reason (R): But they do not produce salt and water when they react with bases.

✅ Answer: (c) – (A) is true but (R) is false

🔹 Explanation:

Assertion is correct – Non-metal oxides like CO₂, SO₂ are acidic.
Reason is false – Acidic oxides do react with bases to form salt and water.

(5)

Assertion (A): Our body works between pH values of 7.0 to 7.8.
Reason (R): When pH value of rainwater is less than 5.6, it is called acid rain.

✅ Answer: (a) – Both (A) and (R) are true and (R) is the correct explanation of (A)

🔹 Explanation:

Human blood has pH ~7.4 (range 7.0 to 7.8 is safe).
Acid rain occurs when pH < 5.6 due to presence of acidic gases like SO₂, NO₂.

MCQ & Very Short Questions

[HSLC Pattern]

(i) The acid is found in curd –
(a) Oxalic acid
(b) Tartaric acid
(c) ✅ Lactic acid
(d) Acetic acid

(ii) The taste of soap solution is bitter because soap solution is a –
(a) ✅ Alkaline
(b) Acidic
(c) Both (a) and (b)
(d) None of these

(iii) When zinc is combined with aqueous solution of sodium hydroxide, production of –
(a) CO₂ gas
(b) N₂ gas
(c) ✅ H₂ gas
(d) SO₂ gas

(iv) When alkali reacts with acid, then production of –
(a) ✅ Salt and water
(b) Salt and hydrogen gas
(c) Water and hydrogen gas
(d) Carbon dioxide and water

(v) In aqueous solution acid releases –
(a) ✅ H⁺ ion
(b) OH⁻ ion
(c) Both (a) and (b)
(d) None

(vi) Hydrochloric acid is a –
(a) Oxyacid
(b) Hydracid
(c) ✅ Both (a) and (b)
(d) Neither (a) nor (b)

(vii) When blue litmus is added to liquid HCl solution, what will be the colour –
(a) Colourless
(b) No change, blue colour
(c) ✅ Red colour
(d) Green colour

(viii) The taste of liquid NaOH is –
(a) Soar
(b) ✅ Bitter
(c) Sweet
(d) Salted

(ix) Which of the following gas will be produced when liquid sulphuric acid is added to a piece of sodium hydroxide –
(a) ✅ H₂
(b) SO₂
(c) H₂S
(d) O₂
(Note: Normally, H₂ gas is not produced in this reaction, but H₂ is given as the answer in the image.)

(x) Methyl orange is –
(a) Red in acidic medium, colourless in basic medium
(b) Yellow in acidic medium, red in basic medium
(c) ✅ Red in acidic medium, yellow in basic medium
(d) Colourless in acidic medium, red in basic medium

(xi) Lemon juice and coffee are –
(a) Red basic
(b) Yellow basic
(c) ✅ Both acidic
(d) Lemon juice is acidic, coffee is basic

(xii) A solution turns red litmus blue, its pH is likely to be –
(a) ✅ 10
(b) 5
(c) 4
(d) 1

(xiii) Which one of the following type of medicine is used for treating indigestion –
(a) ✅ Antacid
(b) Antiseptic
(c) Antibiotic
(d) Analgesic

(xiv) Which among the following is not a base –
(a) ✅ C₂H₅OH
(b) KOH
(c) NH₄OH
(d) NaOH

(xv) Which of the following is used for dissolution of gold?
(a) ✅ Aqua regia
(b) Sulphuric acid
(c) Nitric acid
(d) Hydrochloric acid

(xvi) Which one of the following can be used as an acid-base indicator by a visually impaired student –
(a) Turmeric
(b) Litmus
(c) ✅ Vanilla essence
(d) Petunia leaves

(xvii) An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?
(a) Hydrochloric acid
(b) Ammonium hydroxide solution
(c) Lime
(d) Baking powder
Answer: (a) Hydrochloric acid ✅ [HSLC]

(xviii) Sodium Carbonate is a basic salt because it is a salt of–
(a) strong acid and weak base
(b) weak acid and weak base
(c) strong acid and strong base
(d) weak acid and strong base
Answer: (d) weak acid and strong base ✅ [HSLC]

(xix) Calcium phosphate is present in tooth enamel. Its nature is—
(a) basic
(b) acidic
(c) neutral
(d) amphoteric
Answer: (a) basic ✅ [HSLC]

(xx) Which of the following gives the correct increasing order of acid strength?
(a) Hydrochloric acid water Acetic acid
(b) Acetic acid water Hydrochloric acid
(c) Water Hydrochloric acid Acetic acid
(d) Water Acetic acid Hydrochloric acid
Answer: (d) Water Acetic acid Hydrochloric acid ✅ [HSLC]

(xxi) One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is—
(a) sulphuric acid
(b) acetic acid
(c) tartaric acid
(d) hydrochloric acid
Answer: (c) tartaric acid ✅ [HSLC]

(xxii) To protect tooth decay we are advised to brush our teeth regularly. The nature of tooth paste commonly used—
(a) Neutral
(b) acidic
(c) corrosive
(d) basic
Answer: (d) basic ✅ [HSLC]

(xxiii) Which one of the following salts does not contain water of crystallisation?
(a) Blue vitrol
(b) Baking soda
(c) Washing soda
(d) Gypsum
Answer: (b) Baking soda ✅ [HSLC]

(xxiv) Brine is an—
(a) aqueous solution of sodium bicarbonate
(b) aqueous solution of sodium chloride
(c) aqueous solution of sodium carbonate
(d) aqueous solution of sodium hydroxide
Answer: (b) aqueous solution of sodium chloride ✅ [HSLC]

(xxv) Borax is manufactured from–
(a) washing soda
(b) baking powder
(c) bleaching powder
(d) baking soda
Answer: (a) washing soda ✅ [HSLC]

(xxvi) Alkalis are–
(a) acids, which are soluble in water
(b) bases, which are soluble in water
(c) acids, which are insoluble in water
(d) bases, which are insoluble in water
Answer: (b) bases, which are soluble in water ✅ [HSLC]

(xxvii) Lime water reacts with chlorine to give–
(a) baking soda
(b) washing soda
(c) bleaching powder
(d) baking powder
Answer: (c) bleaching powder ✅ [HSLC]

(xxviii) Sodium hydroxide is used—
(a) weak acid
(b) weak base
(c) strong acid
(d) strong base
Answer: (d) strong base ✅ [HSLC]

(xxix) Sodium hydroxide is used—
(a) as an antacid
(b) in manufacture of soap
(c) in alkaline batteries
(d) as a cleansing agent
Answer: (b) in manufacture of soap ✅ [HSLC]

(xxx) Salt used in food is–
(a) sodium sulphate
(b) sodium hydroxide
(c) calcium chloride
(d) sodium chloride
Answer: (d) sodium chloride ✅ [HSLC]

(xxxi) A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue?
(a) Vinegar
(b) Lemon juice
(c) Common salt
(d) An antacid
Answer: (d) An antacid ✅ [HSLC]

Fill in the blanks:

1. Due to presence of _____ acid, the taste of citrus is sour.
Answer: citric [HSLC]

2. _____ acid is found in orange.
Answer: Citric [HSLC]

3. _____ acid is found in gastric juice.
Answer: Hydrochloric [HSLC]

4. All the alkali are base but all the bases are _____.
Answer: not alkali [HSLC]

5. _____ is dissolved in soda water that is why acidic in nature.
Answer: Carbon dioxide [HSLC]

6. Acids and alkali are _____.
Answer: electrolytes [HSLC]

7. When nitric acid reacts with metal, production of nitrate of metal, _____, _____, nitrogen gas.
Answer: hydrogen, oxides [HSLC]

8. When manganese reacts with dilute nitric acid production of _____ gas.
Answer: hydrogen [HSLC]

9. When acid reacts with base, production of _____ and _____.
Answer: salt, water [HSLC]

10. The base releases _____ ion in aqueous solution.
Answer: OH⁻ (hydroxide) [HSLC]

11. _____ change the red litmus into blue litmus.
Answer: Bases [HSLC]

12. When base reacts with oxides of metal, production of _____ and _____.
Answer: salt, water

13. Hydracids are binary compounds.

14. Perchloric acid is an acid of halogen.

15. Phenolphthalein is a basic indicator and the colour of it is pink in basic solution.

16. pH of basic solution is always more than 7.

17. Sodium bicarbonate is used in soda-acid fire extinguishers.

18. Bleaching powder is used for disinfecting drinking water to make it free of germs.

19. Lime stone is one of the raw materials for the production of baking soda.

20. During indigestion the stomach produces too much acid, and this causes pain and irritation.

True or False:

(i) When acid reacts with metals, production of hydrogen gas and salts of metal. – True
(ii) When magnesium reacts with dilute nitric acid, production of carbon dioxide gas. – False
(iii) When acid reacts with bicarbonate then production of carbon dioxide. – True
(iv) Acids reacts with oxides of metal to produce salt and water. – False
(v) Acids bases are non-electrolytes. – False
(vi) The anion of arsenic acid is arsenite. – False
(vii) Litmus is a oxidation-reduction indicator. – False
(viii) The red litmus is often changed into blue colour in acidic medium. – False
(ix) Phenolphthalein is a natural indicator. – False
(x) Both bases and alkalis are soluble in water. – False
(xi) To get optimum pH of an acidic soil, it is treated with dilute carbonic acid. – False
(xii) Copper sulphate crystals are always wet due to presence of water of crystallisation in them. – True
(xiii) Plaster of Paris should be stored in moisture proof container. – True
(xiv) Bleaching powder reacts with dilute acids to produce chlorine. – True
(xv) Both bases and alkalis are soluble in water. – False

Very Short Answer Type Questions

Name the acid which is found in vinegar.
→ Acetic acid
What do you mean by acid?
→ Acids are substances that release hydrogen ions (H⁺) in aqueous solution.
What is called concentrated acid? Give example.
→ An acid that contains very little water is called concentrated acid. Example: Concentrated sulphuric acid.
What is called dilute acid? Give example.
→ An acid that contains more water than acid is called dilute acid. Example: Dilute hydrochloric acid.
What is called base? Give example.
→ A base is a substance that can accept hydrogen ions or donate a pair of valence electrons. Example: Sodium hydroxide (NaOH).
What is called alkali? Give example.
→ A base that dissolves in water is called an alkali. Example: Potassium hydroxide (KOH).
Name one each of concentrated base and dilute base.
→ Concentrated base: NaOH solution, Dilute base: Dilute NH₄OH
What change will be seen when blue litmus solution is added to the citrus juice?
→ It will turn red, as citrus juice is acidic.

12. How will you prove that the orange juice is either acidic or basic with the help of litmus?
→ Add blue litmus to the orange juice. If it turns red, it is acidic.

13. Why is lime water basic in nature?
→ Lime water contains calcium hydroxide (Ca(OH)₂), a base, which makes it basic in nature.

14. Why are the fruit juice and curd not kept in the pot of bell metal?
→ Because bell metal contains copper, and acids in fruit juice and curd react with copper forming toxic compounds.

15. What is called oxyacid? Give example.
→ Acids that contain oxygen, hydrogen, and another element are called oxyacids.
Example: H₂SO₄ (Sulphuric acid).

16. Name the plants from where the litmus pigment can be obtained?
→ Lichens

17. What is called indicator? Give example.
→ Substances that show a colour change in acids and bases.
Example: Litmus, Phenolphthalein

18. What do you mean by a factory indicator?
→ Synthetic indicators prepared in laboratories.
Example: Methyl orange, Phenolphthalein

19. Write the reaction between metal oxide and dilute HCl.
→ Metal oxide + Dilute HCl → Salt + Water
Example:
CuO + 2HCl → CuCl₂ + H₂O

20. Why are metallic oxides called basic oxides?
→ Because they react with acids to form salt and water, showing basic nature.

21. What is universal indicator?
→ A mixture of indicators that shows a wide range of pH values with different colours.

22. What is pH?
→ A scale used to measure the acidity or basicity of a solution; ranges from 0 to 14.

23. What are acidic salts? Give examples.
→ Salts that are formed from a strong acid and weak base.
Example: NH₄Cl, CuSO₄

24. What are basic salts? Give examples.
→ Salts that are formed from a strong base and weak acid.
Example: Sodium acetate (CH₃COONa)

25. Name the products which are formed from the chloro-alkali process.
→ Chlorine (Cl₂), Sodium hydroxide (NaOH), Hydrogen (H₂)

26. Write the chemical formulae of the following salts:
Baking soda → NaHCO₃
Bleaching powder → CaOCl₂

27. What type of pH should the soil have for health growth of plant?
→ Neutral to slightly acidic (pH around 6 to 7)

28. Which acid is injected into our body by a bee-setting that cause pain?
→ Methanoic acid (Formic acid)

29. What do you mean by hygroscopic nature of common salt?
→ The ability to absorb moisture from the air.

30. What is the common name of sodium hydrogen carbonate?
→ Baking soda

31. Name one metal carbonate which is soluble in water and one which is insoluble in water.
→ Soluble: Sodium carbonate (Na₂CO₃)
→ Insoluble: Calcium carbonate (CaCO₃)

32. Where is hydrogen used as a fuel?
→ In fuel cells and rockets.

33. Out of tape water, sea water and pure water, which is the best conductor of electricity?
→ Sea water (due to high salt content)

34. Why is sulphuric acid called “King of Chemicals”?
→ Because it is used widely in the manufacture of many industrial and chemical products.

B. Short Type Questions (Marks: 2/3)

1. What is an acid base indicator? Give two examples of synthetic acid-base indicators.
→ Acid-base indicators are substances that change colour when added to acidic or basic solutions.
Examples: Phenolphthalein, Methyl orange

2. What is the difference between strong acid and weak acid? Give two examples from each.
→ Strong acid: Completely ionizes in water.
Examples: HCl, HNO₃
→ Weak acid: Partially ionizes in water.
Examples: CH₃COOH, H₂CO₃

3. What is the difference between strong base and weak base? Give two examples from each.
→ Strong base: Completely dissociates in water.
Examples: NaOH, KOH
→ Weak base: Partially dissociates in water.
Examples: NH₄OH, Ca(OH)₂

4. Choose strong and weak acids and strong and weak bases from the following:
Strong acids: HNO₃, HCl
Weak acids: CH₃COOH, H₂CO₃
Strong bases: NaOH
Weak bases: NH₄OH, Ca(OH)₂

5. Why do we feel a burning sensation in the stomach when we overeat? What is the medicine used called? Give one example.
Answer: We feel a burning sensation in the stomach when we overeat because of excess acid (HCl) production. This acid irritates the stomach lining. The medicine used to neutralize this acid is called an antacid.
Example: Milk of magnesia (Mg(OH)₂).

6. How is bleaching powder produced? Give the reaction involved.
Answer: Bleaching powder is produced by passing chlorine gas over dry slaked lime (Ca(OH)₂).
Reaction:
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

7. What is the basic theory of the manufacture of baking soda?
Answer: Baking soda is manufactured by the Solvay process. In this, sodium chloride (NaCl), ammonia (NH₃), and carbon dioxide (CO₂) are reacted in water to form sodium bicarbonate (NaHCO₃), which precipitates out.
Equation:
NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl

8. How is plaster of Paris prepared? What reaction takes place?
Answer: Plaster of Paris is prepared by heating gypsum (CaSO₄·2H₂O) at 373 K.
Reaction:
CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O

9. Write the chemical formula of washing soda. What happens when crystals of washing soda are exposed to air?
Answer: Chemical formula of washing soda is Na₂CO₃·10H₂O.
On exposure to air, it loses water of crystallization and becomes a white powder (efflorescence).

10. What does "slinking of lime" stand for? Write the chemical equation for the reaction involved.
Answer: “Slinking of lime” refers to the reaction of quicklime (CaO) with water to form slaked lime (Ca(OH)₂), releasing heat.
Reaction:
CaO + H₂O → Ca(OH)₂ + Heat

11. Given the pH values of four different liquids as 7.0, 14.0, 4.0, 2.0, which of these could be that of -
(i) Lemon juice - 2.0
(ii) Distilled water - 7.0
(iii) 1M sodium hydroxide solution - 14.0
(iv) Tomato juice - 4.0

12. What is “baking powder”? How does it make the cake soft and spongy?
Answer: Baking powder is a mixture of baking soda (NaHCO₃) and a mild acid like tartaric acid.
When heated, it releases CO₂ gas, which makes the cake soft and spongy.

13. Write the chemical formula of bleaching powder. How is bleaching powder prepared? For what purposes is it used in paper industries?
Answer: Formula: CaOCl₂
It is prepared by reacting chlorine gas with dry slaked lime.
Reaction:
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Used in paper industry for bleaching wood pulp.

14. Why does tooth decay start when the pH of the mouth is lower than 5.5?
Answer: Tooth enamel made of calcium phosphate dissolves in acid. When pH drops below 5.5 due to acid produced by bacteria, tooth decay starts.

15. Why should curd not be kept in copper or brass vessels? What is done to protect it?
Answer: Curd is acidic and reacts with copper or brass, forming poisonous compounds. These vessels are often coated with tin to prevent this.

16. Comment on the statement “All alkalies are bases but all bases are not alkalies”.
Answer: Alkalies are water-soluble bases. All alkalies (e.g., NaOH, KOH) are bases, but some bases (like CuO, Fe(OH)₃) are not soluble in water, so not all bases are alkalies.

17. What is acid rain? What is its pH? How does it affect aquatic life?
Answer: Acid rain is rainfall with a pH below 5.6 due to sulfur and nitrogen oxides in the air. It lowers the pH of water bodies, harming aquatic organisms.

18. (a) What is the action of litmus on -
(i) Dry ammonia gas – Red litmus turns blue.
(ii) Solution of ammonia gas in water – Red litmus turns blue.

(b) Observations on adding ammonium hydroxide to aqueous solution of -
(i) Ferrous sulphate – Green ppt of ferrous hydroxide forms.
(ii) Aluminium chloride – White gelatinous ppt of aluminium hydroxide forms.

19. Write any three chemical properties of acids.
Answer:

Acids turn blue litmus red.
Acids react with metals to produce hydrogen gas.
Acids react with carbonates to produce CO₂.

20. Why does bleaching powder give a typical smell in the air?
Answer: Bleaching powder gives a typical smell due to the release of chlorine gas (Cl₂) when it reacts with moisture in air.

21. How will you prepare dilute sulphuric acid from concentrated sulphuric acid? Give reason for your answer.
Answer: Always add acid to water slowly with stirring (never add water to acid).
Reason: The process is exothermic and adding water to acid may cause splashing and burns.

22. Name the natural source of the following acids:
(a) Methanoic acid – Ant sting
(b) Citric acid – Citrus fruits (e.g., lemon, orange)
(c) Oxalic acid – Spinach
(d) Ascorbic acid – Amla (Indian gooseberry), citrus fruits

23. Write down the natural sources of the following acids:
(a) Ethanoic acid – Vinegar
(b) Lactic acid – Sour milk or curd
(c) Tartaric acid – Tamarind, grapes
(d) Hydrochloric acid – Human stomach (gastric juice)

24. Write down four important characteristics of acids:

Acids turn blue litmus red.
They taste sour.
They react with metals to produce hydrogen gas.
They have a pH less than 7.

25. When hydrochloric acid is added to sodium carbonate and sodium bicarbonate, then production of sodium chloride and water is written with a chemical reaction.
Answer:
With sodium carbonate:
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑
With sodium bicarbonate:
NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

26. Mention four important characteristics of base:

Bases turn red litmus blue.
They taste bitter.
They feel soapy to touch.
They have a pH more than 7.

27. When acid reacts with metal, what is the name of gas which is produced from this reaction? Write with a chemical reaction.
Answer: Hydrogen gas is produced.
Example: Zn + 2HCl → ZnCl₂ + H₂↑

28. What will be the colour of turmeric in acid, neutral and basic medium?

Acidic: Yellow
Neutral: Yellow
Basic: Reddish brown

29. What will be the colour of litmus in acid, neutral and basic medium?

Acidic: Blue to red
Neutral: No change
Basic: Red to blue

30. What will be the colour of phenolphthalein in acid, neutral and basic medium?

Acidic: Colourless
Neutral: Colourless
Basic: Pink

31. What will be the colour of methyl orange in acid, neutral and basic medium?

Acidic: Red
Neutral: Orange
Basic: Yellow

32. Write the names of two natural indicators.

Litmus
Turmeric

33. The H₂SO₄ solution is acidic but C₂H₅OH is not acidic. Explain with reasons.
Answer: H₂SO₄ (sulphuric acid) ionizes in water to give H⁺ ions, making it acidic.
C₂H₅OH (ethanol) does not ionize to give H⁺ ions in solution, so it is not acidic.

34. Write down the name of acids and bases which is required to prepare Na₂CO₃ and MgSO₄.

Na₂CO₃: Sodium hydroxide (base) + Carbonic acid (acid)
MgSO₄: Magnesium hydroxide (base) + Sulphuric acid (acid)

35. What will be the action of the following substances on litmus paper?

Dry HCl gas – No change (needs moisture)
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

36. What happens when zinc metal is treated with dilute solution of a strong acid, a gas is evolved. Which is utilized 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.
Answer: The gas evolved is hydrogen (H₂).
Reaction: Zn + 2HCl → ZnCl₂ + H₂↑
Test: Bring a burning matchstick near the gas – it burns with a pop sound confirming H₂.

37. What happens when nitric acid is added to eggshell?
Answer: Eggshells contain calcium carbonate (CaCO₃). When nitric acid is added, carbon dioxide gas is released.
Reaction:
CaCO₃ + 2HNO₃ → Ca(NO₃)₂ + H₂O + CO₂↑

C. Essay Type Questions (Marks: 4/5)

1. For making cake, baking soda instead of baking powder in cake:

(a) How will it affect the taste of the cake and why?
Answer: Using baking soda alone can make the cake taste bitter because it is a base (sodium bicarbonate). Without an acid to react with, it does not neutralize completely, resulting in a bitter taste.

(b) What can baking soda be converted into baking powder?
Answer: Baking powder is a mixture of baking soda (sodium bicarbonate) and a weak acid like tartaric acid. So, baking soda can be converted into baking powder by adding an edible acid.

(c) What is the role of tartaric acid added to baking soda?
Answer: Tartaric acid reacts with baking soda during baking to produce carbon dioxide gas, which helps in rising and making the cake soft and fluffy. It also neutralizes the bitterness of baking soda.

2. Write an activity to show the reaction of acids with metal carbonates and metal hydrogen carbonate salts.
Answer:
Take some dilute HCl in a test tube. Add a pinch of sodium carbonate (Na₂CO₃) or sodium hydrogen carbonate (NaHCO₃). You will observe brisk effervescence due to the formation of CO₂ gas.

Reaction:

3. (a) What do you mean by ionic product of water and pH value?
Answer:
The ionic product of water (Kw) is the product of the concentrations of H⁺ and OH⁻ ions in pure water.

pH is the negative logarithm of the hydrogen ion concentration:

(b) You are given 1 M H₂SO₄ solution. How will you prepare from it 400 mL of a solution with pH = 2?
Answer:
pH = 2 means [H⁺] = 10⁻² M.
Since H₂SO₄ is a strong acid and gives 2 H⁺ per molecule, we need 0.005 M H₂SO₄.
Use dilution formula:

Take 2 mL of 1 M H₂SO₄ and dilute it to 400 mL.

(c) Using solid NaOH, how will you prepare 400 mL of a solution with pH = 12?
Answer:
pH = 12 → pOH = 2 → [OH⁻] = 10⁻² M
Molarity = 0.01 M; Volume = 400 mL = 0.4 L
Moles = M × V = 0.01 × 0.4 = 0.004 mol
Mass = moles × molar mass = 0.004 × 40 = 0.16 g NaOH
Dissolve 0.16 g NaOH in 400 mL of water.

4. (a) Name three important mineral acids. Give two important uses of each of them.
Answer:

Hydrochloric acid (HCl):
- Used in cleaning metals
- Used in the manufacture of medicines
Sulphuric acid (H₂SO₄):
- Used in car batteries
- Used in the production of fertilizers
Nitric acid (HNO₃):
- Used in the manufacture of explosives
- Used in making dyes and fertilizers

(b) What is the difference between a normal salt and an acidic salt? Explain with example.
Answer:

Normal Salt: Formed when all replaceable hydrogen atoms of acid are replaced.
Example: NaCl (from HCl and NaOH)
Acidic Salt: Formed when partial hydrogen atoms of a polybasic acid are replaced.
Example: NaHSO₄

5. (a) How will you classify different types of oxides into three main categories? Explain with suitable examples.
Answer:

Acidic Oxide: Non-metal oxides that form acid in water.
Example: CO₂ + H₂O → H₂CO₃
Basic Oxide: Metal oxides that form base in water.
Example: Na₂O + H₂O → 2NaOH
Amphoteric Oxide: Oxides that react with both acids and bases.
Example: Al₂O₃
[HSLC]

(b) What is the difference between a base and an alkali? Explain with suitable examples.
Answer:

Base: Substances that neutralize acids. Example: CuO
Alkali: Bases that dissolve in water. Example: NaOH
All alkalis are bases, but not all bases are alkalis. [HSLC]

6. How can you classify salts into different types? Give two examples of each type.
Answer:

Normal Salt: NaCl, K₂SO₄
Acidic Salt: NaHSO₄, NaHCO₃
Basic Salt: Mg(OH)Cl, Zn(OH)Cl
Double Salt: Mohr's salt, Potash alum

7. How is common salt found in nature? Give any four important uses of common salt.
Answer:

Found in sea water and rock salt deposits.

Uses:

Used in food.
Used in the manufacture of washing soda.
Used in the manufacture of caustic soda.
Used in soap and glass industry.

8. What are the different steps of Solvay’s process for the manufacture of washing soda? Give its important uses.
Answer:
Steps:

Brine solution is saturated with ammonia.
CO₂ is passed to form sodium bicarbonate.
Bicarbonate is filtered, heated to form sodium carbonate.
Sodium carbonate is crystallized to washing soda.

Uses:

Used in softening water
Used in detergent industries
Used in glass and soap manufacturing

Case Study Based Question Answers

Case Study (1): Properties of Acids, Bases, and Salts

1. What is the taste of acids?
Answer: Acids have a sour taste.

2. What ions are produced if bases react with water?
Answer: Bases produce hydroxide ions (OH⁻) when they react with water.

3. What is the effect of salts on litmus paper?
Answer: Salts are neutral substances; their liquid forms have no effect on litmus paper.

Case Study (2): Acid Rain

1. What is acid rain?
Answer: Acid rain is the rain of cloud water containing acidic particles, formed when gases like sulfur dioxide and nitrogen oxides dissolve in rainwater.
[HSLC]

2. With presence of what chemicals, such rains can take place?
Answer: Acid rain is caused by the presence of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere.

3. How acid rains can occur?
Answer: These gases mix with water, oxygen, and other chemicals in the atmosphere and form acids, which then fall as acid rain.
[HSLC]

Case Study (3): Acids and Bases as Ions and Electrolytes

1. Mainly what make Acids and Bases?
Answer:

Acids are made of hydrogen ions (H⁺) and non-metal anions.
Bases are made of hydroxide ions (OH⁻) and metal cations.
[HSLC]

2. What types of ions form Acids?
Answer: Acids form hydrogen ions (H⁺) when dissolved in water.

3. Are acids and bases are electrolytes?
Answer: Yes, both acids and bases are electrolytes, as they produce ions in solution and can conduct electricity.

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