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Question: Aqueous solution of Nickel sulphate on treating with pyridine and then adding a solution of sodium n...

Aqueous solution of Nickel sulphate on treating with pyridine and then adding a solution of sodium nitrate gives dark blue crystals of:
A. [Ni(py)4]SO4[Ni{(py)_4}]S{O_4}
B. [Ni(py)2(NO2)2][Ni{(py)_2}{(N{O_2})_2}]
C. [Ni(py)4(NO2)2][Ni{(py)_4}{(N{O_2})_2}]
D. [Ni(py)3(NO2)]2SO4{[Ni{(py)_3}(N{O_2})]_2}S{O_4}

Explanation

Solution

Nickel sulphate has the molecular formula NiSO4NiS{O_4}. In an aqueous solution, it dissociates to give nickel ion and sulphate ion. Nickel is present under d-block elements since nickel has outermost electrons present in the d- subshell. The d-block elements exhibit variable valency and are mostly formed as stable complexes. The ionization of nickel sulphate in an aqueous solution can be written as,
NiSO4→Ni2++SO42−NiS{O_4} \to N{i^{2 + }} + S{O_4}^{2 - }.

Complete answer:

When nickel sulphate is treated with pyridine, nickel (ii) pyridine complex is formed. Pyridine is a strong field ligand and hence, it replaces sulphate from nickel sulphate solution. The reaction can be written as follows,
NiSO4+Py→[Ni(Py)4]2+SO42−NiS{O_4} + Py \to {[Ni{(Py)_4}]^{2 + }}S{O_4}^{2 - }
The formed complex is further treated with sodium nitrate, it forms dark blue crystals. The reaction can be written as follows,
[Ni(Py)4]2+SO42−+NaNO3→[Ni(Py)4(NO2)2]+Na2SO4{[Ni{(Py)_4}]^{2 + }}S{O_4}^{2 - } + NaN{O_3} \to [Ni{(Py)_4}{(N{O_2})_2}] + N{a_2}S{O_4}.
The complex appeared as the dark blue crystal is Dinitritotetrapyridine-N-nickel (II).
Thus, an aqueous solution of Nickel sulphate on treating with pyridine and then adding a solution of sodium nitrate gives dark blue crystals of [Ni(Py)4(NO2)2][Ni{(Py)_4}{(N{O_2})_2}].

So, the correct answer is Option C.

Note:

The molecular formula for pyridine is C6H5N{C_6}{H_5}N. It is a neutral and strong magnetic field ligand. Generally, pyridine is used as a solvent. It is used in the preparation of vitamins, drugs, and insecticides.

Nickel sulphate present in an aqueous solution can be obtained as hexahydrate and heptahydrate.

Nickel sulphate hexahydrate is blue to emerald in colour.

Nickel sulphate heptahydrate is green in colour.

Nickel sulphate helps to synthesize other nickel compounds.

It acts as mordants in dyes. It is also used in coatings and ceramics. Sodium nitrate is a white crystalline solid.

It is used as a fertilizer.

It is also used in explosives and propellants.