Question

Hydrolysis of a compound A, C7H6cl2 was carried out by refluxing with excess potassium hydroxide solution. the resulting solution was acidified with dilute HNO3 acid and excess silver nitrate was added to precipitate the chloride ions as silver chloride. 0.718g of silver chloride was formed from 0.805g of A.

1. calculate the number of chlorine atoms present in each molecule of A liberated by hydrolysis.

2. Suggest an explanation for result in no.1

Answer 1

%Cl in C7H6Cl2 = (2*35.44/161.03)*100 = 44.02% or 44.0% Cl to 3 s.f.

%Cl from AgCl data.
mols AgCl = g/molar mass = 0.718/143.32 = 0.005. mols Cl = 0.005. g Cl = 0.005x 35.44 = 1.41E-4. %Cl in C7H6Cl2 = (g Cl/mass sample)*100 = (1.41E-4/0.805)*100 = 22.05% or 22.1% to 3 s.f.

So there is 44% Cl in the initial compound but after hydrolysis you found only 22.1% which is just half the value you might expect. That means that 1 of the Cl atoms is attached to a coordination sphere and the other Cl atom is outside the coordination sphere. So the ionic Cl was hydrolyzed