Question

Explain why silver chloride is soluble in aqueous solution of methyl amine.

Answer 1

Hint: Solubility of any compound is dependent on the lattice energy and solvation enthalpies of the salt in the solvent. A salt becomes soluble in a solvent when the solvation enthalpies of the ions formed in the solvent is higher than the lattice enthalpy of the salt.

Complete step by step answer:
First let us understand how a compound is able to dissolve in a given solvent.
Any salt will be soluble in a solvent if the solvation enthalpy is greater than the lattice enthalpy. Solvation enthalpy is the energy released when the ions of a particular salt are dissolved in the solvent, while the lattice enthalpy is the energy holding the ions together in the solute.
Now let us see what happens when silver chloride is dissolved in methyl amine.
What happens is that a coordination compound is formed by the reaction:
$AgCl + 2C{H_3}N{H_2} \to {[Ag{(C{H_3}N{H_2})_2}]^ + }C{l^ - }$
This coordination compound is readily soluble in methyl amine, since it is highly polar in nature, just like methyl amine. The energy released when these ions are released into the solvent are higher than the lattice energy which will keep the ions together. Hence, silver chloride is soluble in an aqueous solution of methyl amine.

Note: Silver chloride is not soluble in water. This is because the energy released when the silver ion and chloride ion are hydrated (dissolved in water) is lesser than the energy which holds them together in the salt form. Note that when it comes to solubility of liquids, polar solvents tend to dissolve polar compounds whereas non polar solvents don’t usually have good solvation abilities. Silver chloride is a white crystalline solid at room temperature.