Answer to Question #167698 in General Chemistry for M3

Question

The reaction of copper(||) carbonate and dilute nitric acid produces copper(||) nitrate. Describe the preparation of copper(||) nitrate crystals by this method including the observations made. Explain each stage of the preparation. [6 marks - 6 QWC]

Answer 1

$CuCO_3(s)+2HNO_3(aq)\longrightarrow Cu(NO_3)_2(aq)+H_2O(l)+CO_2(g)$

Copper metal "dissolves" in nitric acid (HNO₃).The nitrate ion oxidizes the copper metal to copper (II) ion while itself being transformed to NO₂ gas in the process; the copper (II) ion then binds to six water molecules. The physical observed is the copper-coloured metal vanishing as the solution turns blue (from [Cu(H₂O)₆]²⁺, the hexaaquacopper ion) and a brown gas (NO₂) is evolved.

Cu (s) + 4 H₃O⁺ (aq) + 2 NO₃^- (aq) --> [Cu(H₂O)₆]²⁺ (aq) + 2 NO₂ (g)

Hydroxide ion (OH^-) binds to the copper (II) ion even more strongly than does water. As a result, hydroxide ion can displace water from the copper (II) ion, yielding copper hydroxide, Cu(OH)₂, a blue precipitate.

[Cu(H₂O)₆]²⁺ (aq) + 2 OH^- --> Cu(OH)₂ (s) + 6 H₂O (l)