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Question: \(HgC{l_2}\) is a covalent compound sparingly soluble in water, the solubility increases by the addi...

HgCl2HgC{l_2} is a covalent compound sparingly soluble in water, the solubility increases by the addition of chloride ions due to:
A) Common ion effect
B) Formation of a complex [HgCl4]2−{[HgC{l_4}]^{2 - }}
C) Weakening of Hg−ClHg - Cl bonds
D) Strong ion-dipole forces.

Explanation

Solution

We know that a covalent compound is the one which is formed by the sharing of valence electrons in order to complete the octet of each element present in the compound. Covalent compounds are insoluble in water but are soluble in organic solvents. HgCl2HgC{l_2} is a triatomic molecule where the HgHg atom is bonded with two ClCl atoms.

Complete solution:
When Chloride ions will be added to HgCl2HgC{l_2} ,the chemical equation will be written as:
HgCl2+2Cl−→[HgCl4]2−HgC{l_2} + 2C{l^ - } \to {[HgC{l_4}]^{2 - }}
Here we see that formation of an ionic complex is taking place. Ionic compounds are more soluble in water than covalent compounds. Hence a water-soluble complex is obtained which increases the solubility of HgCl2HgC{l_2} when chloride ions will be added into it.
The increase in the solubility could not be because of the common ion effect as we know that when a common ion effect takes place the solubility of the compound always decreases. And also, for the common ion effect to occur the compound must be an ionic compound to form ion after dissociation and here HgCl2HgC{l_2} is a covalent compound.
Also, we know that covalent bonds are very strong and a large amount of energy is required to break a covalent bond so weakening of Hg−ClHg - Cl bond is also not the correct reason and also as HgCl2HgC{l_2} is not a ionic compound so the reason for the increase in solubility could not be strong ion-dipole forces.

Hence the option B is the correct answer.

Note: The solubility of HgCl2HgC{l_2} after the addition of chloride ions increases from 6%6\% at 20∘C20^\circ C to 36%36\% in 100∘C100^\circ C. Also HgCl2HgC{l_2} is considered to be highly toxic in nature as any form of mercury when absorbed is poisonous as it has some corrosive properties which can cause internal damage to stomach, mouth and also cause throat ulcers.