JEE MAIN - Chemistry (2022 - 27th June Morning Shift - No. 16)
The number of statements correct from the following for Copper (at. no. 29) is/are ____________.
(A) Cu(II) complexes are always paramagnetic.
(B) Cu(I) complexes are generally colourless
(C) Cu(I) is easily oxidized
(D) In Fehling solution, the active reagent has Cu(I)
Answer
3
Explanation
(A) $\mathrm{Cu}$ (II) complexes are always paramagnetic as they have one unpaired electron due to $d^{9}$ configuration of $\mathrm{Cu}(\mathrm{II})$
(B) $\mathrm{Cu}(\mathrm{I})$ complexes are generally colourless due to $d^{10}$ configuration.
(C) $\mathrm{Cu}(\mathrm{I})$ is easily oxidised to $\mathrm{Cu}^{+2}$ in aqueous solution
$2 \mathrm{Cu}^{+} \rightarrow \mathrm{Cu}^{+2}+\mathrm{Cu}$
$\mathrm{Cu}^{+1}$ disproportionates to $\mathrm{Cu}^{+2}$ and $\mathrm{Cu}$
$\left(E_{\text {cell }}^{\circ}>0\right.$ for this cell reaction in aqueous solution)
In Fehling's solution, active reagent has $\mathrm{Cu}(\mathrm{II})$ which is reduced to $\mathrm{Cu}(\mathrm{I})$ on reaction with aldehydes.
Hence (D) statement is incorrect
(B) $\mathrm{Cu}(\mathrm{I})$ complexes are generally colourless due to $d^{10}$ configuration.
(C) $\mathrm{Cu}(\mathrm{I})$ is easily oxidised to $\mathrm{Cu}^{+2}$ in aqueous solution
$2 \mathrm{Cu}^{+} \rightarrow \mathrm{Cu}^{+2}+\mathrm{Cu}$
$\mathrm{Cu}^{+1}$ disproportionates to $\mathrm{Cu}^{+2}$ and $\mathrm{Cu}$
$\left(E_{\text {cell }}^{\circ}>0\right.$ for this cell reaction in aqueous solution)
In Fehling's solution, active reagent has $\mathrm{Cu}(\mathrm{II})$ which is reduced to $\mathrm{Cu}(\mathrm{I})$ on reaction with aldehydes.
Hence (D) statement is incorrect
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