CHAPTER – 2: ACIDS, BASES AND SALTS

CHAPTER – 2: ACIDS, BASES AND SALTS

VOLUME – 1

Multiple Choice Questions

1. An aqueous solution ‘A’ turns phenolphthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’, pink colour disappears. Which of the statement is true for solution ‘A’ and ‘B’?
   a) A is strongly basic and B is weak base
   b) A is strongly acidic and B is weak acid.
   c) A has pH greater than 7 and B has pH less than 7.
   d) A has pH less than 7 and B has pH greater than 7.
   Ans. - c) A has pH greater than 7 and B has pH less than 7.
2. Select a pair of olfactory indicators from the following:
   a) Clove oil and turmeric
   b) Onion juice and lemon
   c) Vanilla essence and clove oil
   d) Litmus and methyl orange
   Ans. - c) Vanilla essence and clove oil
3. The acid present in nettle plant is:
   a) Tartaric acid
   b) Oxalic acid
   c) Methanoic acid
   d) Lactic acid
   Ans.- c) Methanoic acid
4. Select the molecule with maximum number of water of crystallisation:
   a) Baking soda
   b) Gypsum
   c) Washing soda
   d) Hydrated copper sulphate
   Ans.- c) Washing soda
5. Which gas is produced when a metal reacts with dilute HCl?
   a) \( CO_2 \)
   b) \( Cl_2 \)
   c) \( O_2 \)
   d) \( H_2 \)
   Ans- d) \( H_2 \)
6. Which of the following is an organic acid?
   a) Hydrochloric acid
   b) Nitric acid
   c) Sulphuric acid
   d) Acetic acid
   Ans- d) Acetic acid
7. Identify the chemical formula of washing soda:
   a) \( NaHCO_3 \)
   b) \( Na_2CO_3 \cdot 5H_2O \)
   c) \( Na_2CO_3 \cdot 10H_2O \)
   d) \( NaOH \)
   Ans- c) \( Na_2CO_3 \cdot 10H_2O \)
8. Identify the pair of weak acids:
   a) \( HCl, CH_3COOH \)
   b) \( HNO_3, HCl \)
   c) \( H_2SO_4, HNO_3 \)
   d) \( CH_3COOH, H_2CO_3 \)
   Ans- d) \( CH_3COOH, H_2CO_3 \)
9. Which of the following is a natural indicator?
   a). Methyl orange
   b). Phenolphthalein
   c). Turmeric
   d). Bromothymol blue
   Answer: c). Turmeric
10. The pH of a neutral solution is:
    a) 0
    b) 7
    c) 14
    d) Between 7 and 14
    Ans- b) 7

Assertion Reason Questions

In each of the questions given below, there are two statements marked as Assertion (A) and Reason (R). Mark your answer as per the codes provided below:

• a) Both A and R are true and R is the correct explanation of A.
• b) Both A and R are true but R is not the correct explanation of A.
• c) A is true but R is false.
• d) A is false but R is true.

11. Assertion (A): Metallic oxides are basic in nature.
    Reason (R): \( MgO \) is a metallic oxide.
    Ans- (a) Both A and R are true, and R is the correct explanation of A
12. Assertion (A): When dry blue litmus paper is exposed to dry HCl gas it turns red.
    Reason (R): Blue litmus turn red in presence of an acid.
    Ans- (d) A is false, but R is true.

Very Short Answer Type Questions

13. Define neutralization reaction with an example.
    OR
    How does a neutralization reaction take place?
    Ans- A neutralization reaction is a chemical reaction in which an acid and a base react to form a salt and water.
    \[ HCl (aq) + NaOH (aq) \rightarrow NaCl (aq) + H_2O (l) \]
14. The pH of a solution of an edible liquid is 4.6. How is the juice likely to be in taste? Also mention the nature of liquid (acidic/basic/neutral).
    Ans- A solution with a pH of 4.6 is likely to taste sour and is acidic. A pH value below 7 indicates acidic nature.
15. Why do acid not show acidic behaviour in the absence of water?
    Ans- In the absence of water, acids do not dissociate to produce \( H^+ \) ions.
16. How is the concentration of \( H_3O^+ \) ions affected when acid is diluted with water?
    Ans- When an acid is diluted with water, the concentration of \( H_3O^+ \) ions decreases.
17. Write an equation to show the reaction between Plaster of Paris and water.
    Ans- \[ CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O \]

Short Answer Type Questions

18. Why it is advised to take precautions while mixing acid with water?
    OR
    Why care should be taken during acid dilution?
    Ans- It is crucial to take precautions when mixing acid with water because the reaction is highly exothermic and it releases a lot of heat. If water is added to concentrated acid, the heat generated can cause the mixture to boil and splash, causing severe burns.
19. Define water of crystallization. Give 2 examples of compound with water of crystallization.
    Ans- Water of crystallization refers to the fixed number of water molecules that are chemically bound within a crystal structure of a compound. Examples – copper (II) sulphate pentahydrate (\( CuSO_4 \cdot 5H_2O \)) and gypsum (\( CaSO_4 \cdot 2H_2O \)).
20. Name the gas evolved when a metal reacts with an acid. How will you test this gas?
    Ans- When a metal reacts with an acid, the gas released is hydrogen gas. A common test for hydrogen gas is to bring a burning matchstick near the gas. If the gas burns with a "pop" sound, it confirms the presence of hydrogen.
21. How baking soda differ from baking powder?
    Ans- Baking soda is a single compound which has sodium hydrogen carbonate which is alkaline basic in nature. Baking powder is a mixture of sodium hydrogen carbonate and a mild edible acid such as tartaric acid.
22. Explain the working of antacid in getting relieve from acidity.
    OR
    Explain how antacids help maintain the pH balance in the stomach.
    Ans- Antacids provide relief from acidity by neutralizing excess stomach acid. They contain bases that react with the hydrochloric acid produced in the stomach, reducing its acidity.

Long Answer Type Questions

23. Give reasons:
    (i) Use of mild base like baking soda provides relief on the areas stung by a honeybee.
    Ans- Bee sting leaves Methanoic acid which causes pain and irritation. Use of mild base like baking soda on the sting area gives relief.
    ii) The colour of copper sulphate crystals changes to white on heating.
    Ans- The blue color of copper sulphate crystals (\( CuSO_4 \cdot 5H_2O \)) changes to white upon heating because the water molecules trapped within the crystal structure, known as water of crystallization, are moved out.
    iii) A solution of baking soda turns red litmus blue.
    Ans- Baking Soda is a mild base and it turns red litmus paper blue.
24. A white powder is used by doctors to support fractured bones
    (i) Write the name and chemical formula of the powder.
    Ans- Plaster of Paris. Its chemical formula is \( CaSO_4 \cdot \frac{1}{2}H_2O \)
    (ii) How is this powder prepared?
    Ans- \[ CaSO_4 \cdot 2H_2O \rightarrow CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \]
    (iii) Give one more use of this powder.
    Ans- In making of pottery and decorative items.
25. i) Write the chemical equation involved in chlor- alkali process?
    Ans- \[ 2NaCl + 2H_2O \rightarrow 2NaOH + Cl_2 + H_2 \]
    ii) What is the substance that are formed at anode and cathode in chlor- alkali process?
    Ans- At anode chlorine gas and at cathode hydrogen gas are formed.
    iii) What are the uses of chlorine?
    Ans- Used for water treatment and pesticides.
    iv) a. Where does the sodium hydroxide solution is formed?
    Ans- It is formed near the cathode.
    b. What are the uses of Sodium hydroxide?
    Ans- Uses in making soaps and detergents.

Case Based Questions

26. Rohit observed that his mother used baking soda to clean kitchen tiles and utensils. Curious, he read on the packet that baking soda is chemically sodium hydrogen carbonate (\( NaHCO_3 \)). He also found out that lemon juice is used to remove stains and bases interact in daily life and decided to do an experiment by mixing both.
    1. Name the type of chemical reaction that occurs when baking soda is mixed with lemon juice.
    Ans- The reaction between baking soda (sodium bicarbonate) and lemon juice (citric acid) is neutralization reaction.
    2. What is the pH range of lemon juice?
    Ans- The pH range of lemon juice is typically between 2 and 3.
    3. (i) What gas is evolved when baking soda reacts with lemon juice?
    OR
    (ii) How can the evolved gas be tested?
    Ans- 3. (i) Carbon dioxide.
    (ii) The presence of carbon dioxide can be tested by bubbling the gas through limewater, which will turn milky.
27. Priya noticed that common salt (\( NaCl \)) is used in cooking, in medicines, and in factories. In her science class, she learned about its production by the neutralization reaction and its use as a raw material in preparing many chemicals like bleaching powder, baking soda, and washing soda.
    1. What is the chemical formula of bleaching powder?
    Ans- \( CaOCl_2 \)
    2. How is bleaching powder prepared?
    \[ Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O \]
    3.(i) How is common salt formed?
    Ans- Common salt (\( NaCl \)) is typically formed by the neutralization reaction between an acid and a base.
    OR
    (ii) Write the reaction involved.
    Ans- One of the most common methods for producing \( NaCl \) is by reacting hydrochloric acid (\( HCl \)) with sodium hydroxide (\( NaOH \)).
    \[ HCl + NaOH \rightarrow NaCl + H_2O \]

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