Question

A 0.5370 g sample of a pure soluble chloride compound is dissolved in water, and all of the chloride ion is precipitated as AgCl by the addition of an excess of silver nitrate. The mass of the resulting AgCl is found to be 1.2523 g.

What is the mass percentage of chlorine in the original compound?

Answer 1

I THINK you may have a typo in your problem. I THINK you want mass percent chloride and not mass percent chlorine.
mols AgCl = 1.2523/molar mass AgCl.
mols Cl^- = same as mols AgCl (because you have 1 mol Cl in 1 mol AgCl).
g Cl^- = mols Cl^- x atomic mass Cl^-
%Cl^- = (mass Cl^-/mass sample)*100 = ?

IF you want mass % chlorine, then go back and find mass Cl2 etc.