Question

Suppose the elements X and Y combine to form two compounds $X{Y}_2$ and $X_3{Y}_2.$ When 0.1 mole of $X{Y}_2$ weighs 10 g and 0.05 mole of $X_3{Y}_2.$ weighs 9 g, the atomic weights of X and Y are

• A. 40, 30
• B. 60, 40
• C. 20, 30
• D. 30, 20

Answer 1

The correct option is A 40, 30

We can use mass and mole balance to solve this.
$0.1x+\left(0.1\right)\left(2\right)y=10$
$\left(0.05\right)\left(3\right)x+\left(0.05\right)\left(2\right)y=9$
Solve these two equations and you get
x = 40, y = 30.