Question

Suppose the elements $X$ and $Y$ combine to form two compounds $XY_2$ and $X_3Y_2$. When $0.1$ mole of $XY_2$ weighs $10\ g$ and $0.05$ mole of $X_3Y_2$ 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

Answer - (a) 40, 30

 

Solution - 

XY₂ ⇒ 0.1 mole = 10g

          1 mole = 100g

X₃Y₂ ⇒ 0.05 mole = 9g

             5 mole = 900g

             1 mole = 180g

Let atomic mass of X = a

Let atomic mass of Y = b

then, molecular mass of XY₂ ⇒ a + 2b = 100g —(1)

         molecular mass of X₃Y₂ ⇒ 3a + 2b = 180g —(2)

Subtracting (1) from (2)

      3a + 2b = 180g 

  (-)  a   + 2b = 100g

2a = 80

a = 40g

b = 30g