A student added acetic acid to test tubes I, II, III and IV containing the labelled substances (I: $NaOH$ , II: $NaCl$ , III: $NaHCO_3$ , IV: $Ca(OH)_2$ ) and then brought a burning splinter near the mouth of each test tube. The splinter would be extinguished when brought near the mouth of test tube

Q: A student added acetic acid to test tubes I, II, III and IV containing the labelled substances (I: $NaOH$, II: $NaCl$, III: $NaHCO_3$, IV: $Ca(OH)_2$) and then brought a burning splinter near the mouth of each test tube. The splinter would be extinguished when brought near the mouth of test tube

The correct option is **C**. When acetic acid ($CH_3COOH$) is added to test tube III containing sodium hydrogencarbonate ($NaHCO_3$), a brisk effervescence of carbon dioxide gas ($CO_2$) is produced: $$CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \uparrow$$ Since carbon dioxide gas does not support combustion, it extinguishes the burning splinter brought near the mouth of test tube III. In the other test tubes, either no reaction occurs (with $NaCl$) or neutralization reactions occur without the evolution of any gas (with $NaOH$ and $Ca(OH)_2$).

Carbon and its Compounds

Chemical Properties of Carbon Compounds

Options

(A)I

(B)II

(C)III

(D)IV

Official Answer

The correct option is C.

When acetic acid ( $CH_3COOH$ ) is added to test tube III containing sodium hydrogencarbonate ( $NaHCO_3$ ), a brisk effervescence of carbon dioxide gas ( $CO_2$ ) is produced:

$CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \uparrow$

Since carbon dioxide gas does not support combustion, it extinguishes the burning splinter brought near the mouth of test tube III. In the other test tubes, either no reaction occurs (with $NaCl$ ) or neutralization reactions occur without the evolution of any gas (with $NaOH$ and $Ca(OH)_2$ ).

sodium hydrogencarbonatecarbon dioxide

CO_2

extinguisheseffervescence

NaHCO_3

Marking Scheme

1Identification of the correct test tube (III) / Option C: 0.5 marks
2Explanation of the reaction producing carbon dioxide gas ( $CO_2$ ) which extinguishes the splinter: 0.5 marks

Hint

Recall that acids react with metal hydrogen carbonates (like $NaHCO_3$ ) to liberate carbon dioxide gas ( $CO_2$ ). Think about which gas among the products of these reactions has the property of extinguishing a fire.

Quick Oral Answer

Question: What gas is evolved when ethanoic acid reacts with sodium hydrogencarbonate, and how do you test it? Answer: Carbon dioxide ( $CO_2$ ) gas is evolved. It can be tested by passing it through lime water, which turns milky due to the formation of calcium carbonate ( $CaCO_3$ ), or by bringing a burning splinter near it, which gets extinguished.

Analysis & Explanation

Why Option C is correct: Acetic acid ( $CH_3COOH$ ) reacts with sodium hydrogencarbonate ( $NaHCO_3$ , present in test tube III) to produce sodium acetate ( $CH_3COONa$ ), water ( $H_2O$ ), and carbon dioxide gas ( $CO_2$ ). The chemical equation is:

$CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \uparrow$

Carbon dioxide ( $CO_2$ ) is a non-combustible gas and does not support combustion, so it extinguishes a burning splinter brought near the mouth of the test tube.

Why other options are incorrect:
Option A (I - $NaOH$ ): Acetic acid reacts with sodium hydroxide ( $NaOH$ ) in a neutralization reaction to form sodium acetate and water. No gas is evolved, so the burning splinter is not extinguished.

$CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O$

Option B (II - $NaCl$ ): Acetic acid does not react with sodium chloride ( $NaCl$ ) under normal conditions, so no gas is evolved.
Option D (IV - $Ca(OH)_2$ ): Acetic acid reacts with calcium hydroxide ( $Ca(OH)_2$ ) to form calcium acetate and water. This is also a neutralization reaction with no gas evolution.

$2CH_3COOH + Ca(OH)_2 \rightarrow (CH_3COO)_2Ca + 2H_2O$

Common Mistakes

1Students might confuse the neutralization reaction of $NaOH$ or $Ca(OH)_2$ with gas-evolving reactions.
2Forgetting that carbon dioxide is the specific gas that extinguishes a burning splinter, whereas hydrogen gas (from metals and acids) burns with a pop sound.

Interesting Facts

Sodium bicarbonate ( $NaHCO_3$ ), commonly known as baking soda, is a key ingredient in dry chemical fire extinguishers because it releases carbon dioxide gas when heated or reacted with acids, smothering the fire.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 1 mark in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Chemical Properties of Carbon Compounds" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a MCQ question from Section B in the CBSE Class 10 Science 2011 paper.