(a) Consider the following diagram. (i) Give the name of the experiment. (ii) What does the experiment demonstrate? (iii) Name one gas that could be used in...
Question 1 Report
(a) Consider the following diagram.
(i) Give the name of the experiment.
(ii) What does the experiment demonstrate?
(iii) Name one gas that could be used in place of HCl gas.
(iv) What colour could be observed in the flask during the spray of water?
(v) Could the gases used in the experiment be collected over water?
(vi) Explain briefly your answer in (a)(v).
(b) A solid substance U when strongly heated decomposes to give a white solid V and carbon (IV) oxide. When water is added to V, W is produced W can be used to test for carbon (IV) Oxide. Identify U, V and W.
Answer Details
The described set-up (a gas in a flask, water sprayed in) is the classic fountain experiment with an acidic gas such as HCl.
(a)(i) Name: the fountain experiment.
(ii) It demonstrates the very high solubility of the gas in water (water rushing up to fill the low-pressure flask).
(iii) A gas that could replace HCl: ammonia (NH3).
(iv) With HCl and litmus in the water, the fountain appears red (the gas is acidic; with ammonia it would appear blue).
(v) No, the gases cannot be collected over water.
(vi) Because they are very soluble in water, so they would dissolve instead of being collected.
(b) U decomposes on heating to a white solid V and carbon(IV) oxide, so U is calcium trioxocarbonate(IV), CaCO3. V reacts with water and its solution tests for CO2, so V is calcium oxide, CaO and W is calcium hydroxide, Ca(OH)2 (lime water).
\(CaCO_3 \rightarrow CaO + CO_2\); \(CaO + H_2O \rightarrow Ca(OH)_2\)
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