Question

Suppose the elements X and Y combine to form two compounds XY₂ and X₃Y₂. When 0.1 mole of XY₂ weighs 10 g and 0.05 mole of X3Y2 weighs 9 g, the atomic weights of X and Y are _______ .

(A) 30, 20 

(B) 40, 30 

(C) 60, 40 

(D) 20, 30

Answer 1

Correct option: (B) 40, 30

0.1 mol of XY₂ = 10 g

∴ 1 mol of XY₂ = 100 g

i.e, Molecular weight of XY₂ = 100

0.05 mol of X₃Y₂ = 9 g

∴ 1 mol of X₃Y₂ = 180 g

i.e., Molecular weight of X₃Y₂ = 180

Let atomic weights of X and Y be x and y respectively.

x + 2y = 100 ….(1)

3x + 2y = 180 ….(2)

Substrating (1) from (2),

2x = 180 - 100

x = 40

Substituting x = 40 in (1),

40 + 2y = 100

∴ y = 30