MCQ

Percentage Composition

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

MCQ

Problem:
10 g of H₂O₂ impure sample when reacted with KI (solution) produced 0.5 g iodine. What is the percentage purity of H₂O₂?
(a) 66.9 %
(b) 0.669 %
(c) 100 %
(d) can't be predicted

Solution:

The reaction is:
$H_{2} O_{2} + 2 KI â†’ I_{2} + 2 KOH$
1 mole of H₂O₂ produce 1 mole of I₂.
Molar mass of H₂O₂= 34 g/mol
mass of H₂O₂= 10 g
Moles of H₂O₂= 10/34 = 0.29 mol
Molar mass of I₂ = 254 g/mol
mass of I₂ = 0.5 g
Moles of I₂ = 0.5/254 = 0.002 mol
0.29 mol of H₂O₂ should produce 0.29 mol of I₂
Purity in H₂O₂ = x %
So, x % of 0.29 = 0.002
$\frac{x}{100} Ã— 0.29 = 0.002$
x = 0.689 %
Closest answer is (b)