Question

Anisha has been given a Test tube with chemical A. When dil. HCl is added to A it
produces a gas that dissolves in water and turns blue litmus red.
(i) Identify A
(ii) Identify the gas released (it turns lime water milky)
Please answer this question as fast as possible

Answer 1

Answer:

(i) The chemical A can be a metal carbonate or a metal bicarbonate.

(ii) The gas evolved is carbon dioxide, CO₂ .

Explanation:

(i) Metal carbonates (MCO₃ , M₂CO₃) and metal hydrogen carbonates or metal bicarbonates [MHCO₃ , M(HCO₃)₂] react with dil. HCl to form metal chloride (salt), water and carbon dioxide gas.

                $metal carbonate / metal bi carbonate \longrightarrow salt + H_{2}O + CO_{2}$

e.g. :

                $Na_{2}CO_{3}(s) + 2HCL(aq) \longrightarrow 2NaCl(aq) + H_{2}O(l) + CO_{2}(g)$

                $CaCO_{3} (s) + 2HCl(aq) \longrightarrow CaCl_{2} (aq) + H_{2}O + CO_{2}$

                $NaHCO_{3} (s) + HCl(aq) \longrightarrow NaCl(aq) + H_{2}O(l) + CO_{2}(g)$

                $Mg(HCO_{3}) _{2}(s) + 2HCl(aq) \longrightarrow MgCl_{2} (aq) + 2H_{2}O(l) + 2CO_{2}(g)$

(ii) The gas evolved in CO₂. It dissolves in water and turns blue litmus red. It also turns lime water milky.

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

                 (lime water)                     (milky white

                                                           precipitate)