Assertion A: The spin only magnetic moment value for is 1.74 BM, whereas for is 5.92 BM. Reason R: In both complexes, Fe is present in +3 oxidation state. [2023]

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Solution

Q.
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: The spin only magnetic moment value for ${[Fe {(CN)}_{6}]}^{3 -}$ is 1.74 BM, whereas for ${[Fe {(H_{2} O)}_{6}]}^{3 +}$ is 5.92 BM.

Reason R: In both complexes, Fe is present in +3 oxidation state.

In the light of the above statements, choose the correct answer from the options given below: [2023]

1 Both A and R are true but R is NOT the correct explanation of A.

2 A is true but R is false.

3 A is false but R is true.

4 Both A and R are true and R is the correct explanation of A.

Ans.
(1)

In ${[Fe {(H_{2} O)}_{6}]}^{3 +},$ $H_{2} O$ is a weak field ligand, so configuration of ${Fe}^{3 +}$ is $t_{2 g}^{1, 1, 1}, e_{g}^{1, 1}$ .

So number of unpaired electrons are 5 and magnetic moment is 5.92 BM.

In ${[Fe {(CN)}_{6}]}^{3 -},$ ${CN}^{-}$ is a strong field ligand, so configuration of ${Fe}^{3 +}$ is $t_{2 g}^{2, 2, 1}, e_{g}^{0, 0}$ .

So number of unpaired electron is 1 and magnetic moment is 1.73 BM.

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