A student takes 2 ml acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He makes the following observations:I. 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 which is brought near it. The correct observations are:(a) I, II and III (b) II, III and IV(c) III, IV and I (d) IV, I and II
Correct Answer: (d) IV, I and II
Explanation: When acetic acid is taken in a dry test tube and sodium hydrogen carbonate is added to it, a colourless and odourless gas evolves with a brisk effervescence i.e., CO2.
$CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2$
Acetic acid + Sodium hydrogencarbonate →Sodium acetate + water + carbon dioxide
When CO2 is passed through lime water, it turns lime water milky because of formation of calcium carbonate ppt.
$Ca(OH)_2(aq) + CO_2(g) → CaCO_3(s) + H_2O$
lime water white ppt
CO2 being a non-supporter of combustion extinguishes the burning splinter when it is brought near it. So, the correct observations are IV, I and II.
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