Class 10 Acids, Bases and Salts Mock Test (CBSE)

Topics in Acids, Bases and Salts

• Acids and bases in the laboratory
• Reaction of acids and bases with metals
• Reaction of metal carbonates and hydrogencarbonates with acids
• Reaction of metallic oxides with acids
• Neutralisation
• Reaction of non-metallic oxides with bases
• Acids and bases in water solution
• pH scale
• Family of salts
• pH of salts
• Chemicals from common salt
• Water of crystallisation

Acids, Bases and Salts practice questions with answers

1. Q1Multiple choice·1 mark
   When a small amount of red-brown iron(III) oxide is reacted with dilute hydrochloric acid, the solution gradually turns yellow-brown. This colour change is due to the formation of which of the following substances?

   1. (a)Iron(III) hydroxide
   2. (b)Iron(II) chloride
   3. (c)Iron(II) hydroxide
   4. (d)Iron(III) chloride
   Show answer and step marks

   1. Correct option: (d) Iron(III) chloride. Iron(III) oxide ($\text{Fe}_2\text{O}_3$) is a basic metallic oxide that reacts with dilute hydrochloric acid to form salt ($\text{FeCl}_3$) and water, imparting a characteristic yellow-brown colour to the solution due to dissolved $\text{Fe}^{3+}$ ions.+1

   Answer: (d)
2. Q2Multiple choice·1 mark
   Which gas is usually liberated when an acid reacts with a metal?

   1. (a)Carbon dioxide
   2. (b)Oxygen
   3. (c)Hydrogen
   4. (d)Nitrogen
   Show answer and step marks

   1. Correct option: (c) Hydrogen+1

   Answer: (c)
3. Q3Assertion and reason·1 mark
   Assertion (A): Dry hydrogen chloride gas does not change the colour of dry blue litmus paper. Reason (R): Hydrogen chloride produces hydrogen ions ($\text{H}^+$) only in the presence of water.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). Dry HCl does not release $\text{H}^+$ ions without water, hence it shows no acidic property.+1

   Answer: (a)
4. Q4Assertion and reason·1 mark
   Assertion (A): The reaction of sodium hydroxide with hydrochloric acid is an exothermic neutralization reaction. Reason (R): Neutralization reactions always result in the formation of a strong base and hydrogen gas.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (c)+1

   Answer: (c)
5. Q5Short answer·2 marks
   Two aqueous solutions, P and Q, have pH values of 3 and 11 respectively. Solution P is reacted with zinc granules, while solution Q is reacted with carbon dioxide gas. State the nature of the products formed in each reaction and identify which solution contains a higher concentration of hydroxide ions ($\text{OH}^-$).
   Show answer and step marks

   1. P (acidic) reacts with zinc to form a salt (zinc salt) and hydrogen gas.+0.5
   2. Q (basic) reacts with carbon dioxide, an acidic non-metallic oxide, to form a salt (a carbonate) and water.+0.5
   3. Q has the higher pH (11), so it has the higher concentration of $\text{OH}^-$ ions.+1

   Answer: P forms salt and hydrogen gas; Q forms salt and water; Solution Q has a higher $[\text{OH}^-]$.
6. Q6Long answer·5 marks
   (a) Define water of crystallisation with a suitable chemical example. (b) Describe an activity with a labeled observation to demonstrate that copper sulphate crystals contain water of crystallisation. Write the chemical equation for the reaction involved when water is added back to the anhydrous salt.
   Show answer and step marks

   1. Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.+1
   2. Example, any one of: copper sulphate pentahydrate $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$; washing soda $\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$; gypsum $\text{CaSO}_4 \cdot 2\text{H}_2\text{O}$; green vitriol $\text{FeSO}_4 \cdot 7\text{H}_2\text{O}$; or any other valid hydrated salt.+1
   3. Activity: heat a few blue copper sulphate crystals in a dry boiling tube over a flame.+1
   4. Observation: the blue crystals turn white, and water droplets collect on the inner walls of the tube.+1
   5. Adding a few drops of water to the white anhydrous salt turns it blue again: $\text{CuSO}_4(s) + 5\text{H}_2\text{O}(l) \to \text{CuSO}_4 \cdot 5\text{H}_2\text{O}(s)$.+1

   Answer: (a) The fixed number of water molecules in one formula unit of a salt, e.g. $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ (or any other valid hydrated salt). (b) On heating blue copper sulphate crystals in a dry tube they turn white and water droplets form on the walls; adding water turns the white powder blue again: $\text{CuSO}_4 + 5\text{H}_2\text{O} \to \text{CuSO}_4 \cdot 5\text{H}_2\text{O}$.

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