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The d- and f-Block Elements — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe d- and f-Block Elements2 Marks
Question
Anhydrous $CuSO _4$ is white but hydrated $CuSO _4$ is blue while both contain $Cu ^{2+}$ ions. Why?
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Answer

Anhydrous $CuSO _4$ and $CuSO _4 .5 H _2 O$ (hydrated copper sulphate) both have $Cu ^{+2}$ which has one unpaired electrons ( $3 d^9$ ) but in anhydrous $CuSO _4$, without $H _2 O$ (ligand), there is no splitting of $d$-orbitals into $t _{2 g}$ and $e _{ g }$ orbitals, could happen. Hence $d-d$ transition does not occur hence it is colourless. Whereas $d-d$ transition occurs in hydrated $CuSO _4$, hence it is blue.

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