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Class 12 NEET Chemistry D And F Block Elements Questions

Question : 113 of 116

Marks: +1, -0

ammonium hydroxide dissolves in copper sulphate
copper sulphate solution reacts with $\mathrm{K}_{4}[\mathrm{Fe}(\mathrm{CN})_{6}]$
ferric chloride reacts with sod. ferrocyanide
anhydrous $\mathrm{CuSO}_{4}$ is dissolved in water.

Solution:

Concept: Characteristic colours of transition metal complexes and precipitates.

Explanation:

Let us analyze the colour changes in each reaction:

When ammonium hydroxide is added to copper sulphate, a deep blue solution of $[\mathrm{Cu}(\mathrm{NH_3})_4]\mathrm{SO_4}$ is formed.
When ferric chloride reacts with sodium ferrocyanide, a Prussian blue precipitate of $\mathrm{Fe_4}[\mathrm{Fe}(\mathrm{CN})_6]_3$ is formed.
When anhydrous $\mathrm{CuSO_4}$ (which is white) is dissolved in water, it forms a blue solution due to the formation of hydrated copper ions $[\mathrm{Cu}(\mathrm{H_2O})_4]^{2+}$ .
When copper sulphate solution reacts with potassium ferrocyanide $\mathrm{K_4}[\mathrm{Fe}(\mathrm{CN})_6]$ , a chocolate brown precipitate of cupric ferrocyanide $\mathrm{Cu_2}[\mathrm{Fe}(\mathrm{CN})_6]$ is formed.

Thus, a blue colouration is not obtained in the reaction of copper sulphate with

\mathrm{K_4}[\mathrm{Fe}(\mathrm{CN})_6]

Answer: Option B

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