Question

a substance X used in a material and is insoluble in water. when X reacted with dilute HCl it produces a gas which turns limewater milky. predict the substance X and write the chemical equations involved.

Answer 1

The substance X is Calcium Carbonate or limestone. When it reacts with Hydrochloric acid, it forms calcium chloride, water and carbon dioxide and carbon dioxide is the gas which turns limewater milky.

CaCO3 + 2HCl = CaCl2 + H2O + CO2

Answer 2

❖ The substance X liberates a gas which turns limewater milky,

∴ The gas evolved is carbon dioxide and the substance X is some metal carbonate because metal carbonates liberate carbon dioxide with dilute acids like dilute HCl.

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❖ The metal carbonate is insoluble in water and is used as building materials,

∴ X is limestone or marble, i.e., calcium carbonate $\sf (CaCO_{3})$.

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✬ The reactions are as follows :

$\sf CaCO_{3} (s) + 2HCl (aq) \: ⟶ \: CaCl_{2}(aq) + H_{2}O (l) + CO_{2} (g)$

$\sf Ca(OH)_{2} (aq) + CO_{2} (g) \: ⟶ \: CaCO_{3} (s) + H_{2}O (l)$