Question

A sample of copper metal is dissolved is 6M nitric acid to liberate a colourless gas (A). Then water is evaporated to leave a blue solid (B) When the blue solid is heated, mixture of gases were produced along with black residue (C). Which of the following is/are correct?

• A. Gaseous mixture liberated on heating solid (B) is $NO_2$ and $O_2$
• B. Bond order of gas (A) is 2.5
• C. Black residue is $CuO$
• D. Gas A is angular molecule

Answer 1

Answer: (A), (B), (C)

A, B, C

Answer 2

Copper reacts with 6M $HNO_3$ to produce colourless NO gas (A) and aqueous $Cu(NO_3)_2$. Evaporating water yields solid blue $Cu(NO_3)_2$ (B). Heating $Cu(NO_3)_2$ decomposes it into black CuO residue (C) and a gaseous mixture of $NO_2$ and $O_2$. Statement A is correct as the gases produced are $NO_2$ and $O_2$. Statement C is correct as the black residue is CuO. Statement B is correct because the bond order of NO (A) is calculated using MO theory to be 2.5. Statement D is incorrect as diatomic molecules like NO are linear, not angular.