Question

Wavelength of red light is absorbed by the complex

• A. $[Cu(CN{)}_4{]}^{2-}$
• B. $[Cu(N{H}_3{)}_4{]}^{2+}$
• C. $CuS{O}_4$
• D. $Cu(CN{)}_2$

Answer 1

Answer: (B)

When $N{H}_{4}OH$ is added to the solution containing $C{u}^{2+}$ ions, deep blue solution is obtained.

$C{u}^{2+}+4N{H}_{4}OH\to \underset{\text{deep blue solution}}{[Cu(N{H}_3{)}_4{]}^{2+}}\to +4H_{2}O$
Hydrated cupric compounds absorb radiations corresponding to red light and the transmitted colour is greenish blue (which is complementary to red colour). Thus, cupric compounds give greenishblue colour.