MCQ

Percentage Composition

By Sakshi Goel | 19 May'20 | 1 K Views

MCQ

Problem:
A mixture of pure AgCl and AgBr contains 60.94% Ag by mass. What is % of AgCl in sample?
(a) 80.36 %
(b) 19.64 %
(c) 4.8 %
(d) 34.19 %

Solution:

Consider weight of sample mixture = 1 g
Let mass of AgCl = x g
Mass of AgBr = (1 - x) g
Molar mass of AgCl = 143.5 g/mol
Molar mass of AgBr = 188 g/mol
molar mass of Ag = 108 g/mol
Mass % of Ag in AgCl = $\frac{108}{143.5} Ã— 100 = 75.3 %$
Similarly, mass % Ag in AgBr = $\frac{108}{188} Ã— 100 = 57.4 %$
Total % Ag in mixture = 60.94 %
So, (75.3 % of x) + (57.4 % of (1-x)) = 60.94 % of 1 g
0.753x + 0.574(1-x) = 0.6094
0.753x + 0.574 - 0.574x = 0.6094
0.179x = 0.0354
x = 0.198 g
% AgCl in sample = $\frac{0.198}{1} Ã— 100 = 19.8 %$
Closest option is (b).