Q25
1 markMCQSection SECTION-B

Four students studied reactions of zinc and sodium carbonate with dilute hydrochloric acid and dilute sodium hydroxide solutions and presented their results as follows. The (✓) shows evolution of gas and (-) shows no reaction. The right set is:

Acids, Bases and Salts
Chemical Properties of Acids and Bases

Options

(A)HCl\text{HCl}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (✓); NaOH\text{NaOH}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (✓)
(B)HCl\text{HCl}: Zn\text{Zn} (-), Na2CO3\text{Na}_2\text{CO}_3 (✓); NaOH\text{NaOH}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (✓)
(C)HCl\text{HCl}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (✓); NaOH\text{NaOH}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (-)
(D)HCl\text{HCl}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (-); NaOH\text{NaOH}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (✓)
Official Answer

The correct option is C: HCl\text{HCl}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (✓); NaOH\text{NaOH}: Zn\text{Zn} (✓), Na2CO3\text{Na}_2\text{CO}_3 (-).

ZincSodium carbonateHydrochloric acidSodium hydroxideHydrogen gasCarbon dioxide

Marking Scheme

  • 10.5 marks
  • 20.5 marks

Hint

Recall that acids react with both metals and carbonates to release gases (H2\text{H}_2 and CO2\text{CO}_2 respectively). Strong bases like NaOH\text{NaOH} react with active metals like Zn\text{Zn} to release H2\text{H}_2 gas, but they do not react with basic salts like Na2CO3\text{Na}_2\text{CO}_3.

Quick Oral Answer

Zinc reacts with dilute hydrochloric acid to evolve hydrogen gas, and with sodium hydroxide to form sodium zincate and hydrogen gas. Sodium carbonate reacts with hydrochloric acid to evolve carbon dioxide gas, but it does not react with sodium hydroxide.

Analysis & Explanation

Based on the chemical properties of acids and bases described in the NCERT text:

  1. Reaction of Zinc with Hydrochloric Acid (HCl\text{HCl}): Metals react with acids to displace hydrogen and form a salt, evolving hydrogen gas.

Zn(s)+2HCl(aq)ZnCl2(aq)+H2(g)\text{Zn}(s) + 2\text{HCl}(aq) \rightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)\uparrow

Thus, gas is evolved (✓).


  1. Reaction of Sodium Carbonate with Hydrochloric Acid (HCl\text{HCl}): Metal carbonates react with acids to produce salt, water, and carbon dioxide gas.

Na2CO3(s)+2HCl(aq)2NaCl(aq)+H2O(l)+CO2(g)\text{Na}_2\text{CO}_3(s) + 2\text{HCl}(aq) \rightarrow 2\text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow

Thus, gas is evolved (✓).


  1. Reaction of Zinc with Sodium Hydroxide (NaOH\text{NaOH}): Zinc is an amphoteric metal and reacts with strong bases like sodium hydroxide on warming to form sodium zincate and hydrogen gas.

2NaOH(aq)+Zn(s)Na2ZnO2(s)+H2(g)2\text{NaOH}(aq) + \text{Zn}(s) \rightarrow \text{Na}_2\text{ZnO}_2(s) + \text{H}_2(g)\uparrow

Thus, gas is evolved (✓).


  1. Reaction of Sodium Carbonate with Sodium Hydroxide (NaOH\text{NaOH}): Sodium carbonate is a basic salt and does not undergo any reaction with a strong base like sodium hydroxide. No gas is evolved (-).

Therefore, Option C correctly represents these observations.

Common Mistakes

  1. 1Students often assume that bases do not react with metals at all, forgetting that zinc reacts with sodium hydroxide to form sodium zincate and hydrogen gas.
  2. 2Students might incorrectly assume that sodium carbonate reacts with sodium hydroxide because both contain sodium.

Interesting Facts

Zinc is one of the few metals that can react with both acids and strong bases to produce hydrogen gas because of its amphoteric nature.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2014?

This question carries 1 mark in the CBSE Class 10 Science 2014 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Acids, Bases and Salts" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Chemical Properties of Acids and Bases" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2014 paper?

This is a MCQ question from Section SECTION-B in the CBSE Class 10 Science 2014 paper.