1 markMCQSection A

When Sodium bicarbonate reacts with dilute hydrochloric acid, the gas evolved is :

Q: When Sodium bicarbonate reacts with dilute hydrochloric acid, the gas evolved is :

The correct option is (c). When sodium bicarbonate ($NaHCO_3$) reacts with dilute hydrochloric acid ($HCl$), carbon dioxide ($CO_2$) gas is evolved, which turns lime water ($Ca(OH)_2$) milky due to the formation of a white precipitate of calcium carbonate ($CaCO_3$).

Acids, Bases and Salts

Reaction of Metal Carbonates and Hydrogencarbonates with Acids

Options

(a)Hydrogen; it gives pop sound with burning match stick.

(b)Hydrogen; it turns lime water milky.

(c)Carbon dioxide; it turns lime water milky.

(d)Carbon dioxide; it blows off a burning match stick with a pop sound.

Official Answer

The correct option is (c). When sodium bicarbonate ( $NaHCO_3$ ) reacts with dilute hydrochloric acid ( $HCl$ ), carbon dioxide ( $CO_2$ ) gas is evolved, which turns lime water ( $Ca(OH)_2$ ) milky due to the formation of a white precipitate of calcium carbonate ( $CaCO_3$ ).

Sodium bicarbonateHydrochloric acidCarbon dioxideLime waterMilkyCalcium carbonate

Marking Scheme

11 Mark for selecting the correct option (c) with correct justification of the chemical reaction.

Hint

Recall the reaction of metal hydrogencarbonates with acids. The gas evolved is also produced during respiration and forms a white precipitate when passed through calcium hydroxide solution.

Quick Oral Answer

When sodium bicarbonate reacts with dilute hydrochloric acid, carbon dioxide gas is evolved. We can confirm its presence by passing it through lime water, which turns milky due to the formation of insoluble calcium carbonate.

Analysis & Explanation

When sodium bicarbonate (a metal hydrogencarbonate) reacts with dilute hydrochloric acid, it produces sodium chloride, water, and carbon dioxide gas. The balanced chemical equation is:

$NaHCO_3(s) + HCl(aq) \rightarrow NaCl(aq) + H_2O(l) + CO_2(g)$

When the evolved carbon dioxide gas is passed through lime water (calcium hydroxide solution), it reacts to form insoluble calcium carbonate, which makes the solution turn milky:

$Ca(OH)_2(aq) + CO_2(g) \rightarrow CaCO_3(s) + H_2O(l)$

Why Option (c) is correct: It correctly identifies the gas as carbon dioxide ( $CO_2$ ) and its characteristic test of turning lime water milky.
Why Option (a) is incorrect: Hydrogen gas is not evolved in this reaction; hydrogen is typically evolved when metals react with acids.
Why Option (b) is incorrect: Hydrogen gas does not turn lime water milky.
Why Option (d) is incorrect: While carbon dioxide does extinguish a burning match stick (as it does not support combustion), it does not produce a pop sound. The pop sound is characteristic of burning hydrogen gas.

Common Mistakes

1Confusing the test for hydrogen gas (pop sound) with the test for carbon dioxide gas (lime water turning milky).
2Writing incorrect chemical formulas for sodium bicarbonate ( $NaHCO_3$ ) or calcium carbonate ( $CaCO_3$ ).

Interesting Facts

Carbon dioxide is denser than air and does not support combustion, which is why it is widely used in fire extinguishers to smother fires.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 1 mark in the CBSE Class 10 Science 2023 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 "Reaction of Metal Carbonates and Hydrogencarbonates with Acids" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2023 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2023 paper.