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A student takes about 2 mL ethanoic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He reports the following observations - Science

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A student takes about 2 mL ethanoic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He reports the following observations:

I. Immediately a colourless and odourless gas evolves with a brisk effervescence.

II. The gas turns lime water milky when passed through it.

III. The gas burns with an explosion when a burning splinter is brought near it.

IV. The gas extinguishes the burning splinter that is brought near it.

The correct observations are

(A) I, II and III

(B) II, III and IV

(C) III, IV and I

(D) I, II and IV

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Solution 1

When sodium hydrogen carbonate is added to a test tube containing ethanoic acid, the following reaction occurs in the test tube:

CH3COOH + NaHCO3 CH3COONa + H2O + CO2

In this reaction, carbon dioxide gas is evolved immediately. It turns the lime water milky. As carbon dioxide gas is a non-supporter of combustion, it will extinguish the burning splinter.

Hence, the correct option is D.

Solution 2

(D) I, II and IV

Statements I, II and IV are true. The carbon dioxide gas gets liberated. It is colourless, odourless and turns lime water milky. The gas extinguishes the burning splinter when brought near it. This is because; carbon dioxide does not burn or support combustion.

Concept: Chemicals from Common Salt (Uses of Salt) - Preparation and Uses of Baking Soda
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