Suppose the elements X and Y combine to form two compounds of `XY_(2) and X_(3)Y_(2)`. When 0.1 mole of `XY_(2)` weighs 10 g and 0.05 mole of `X_(3)Y_(2)` weighs 9 g , what are tha atomic masses of X and Y ?

Options

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

Answer

A

Explanation

Let atomic weight of elements X is x and that of element Y is y.
For `XY_(2)`
0.1 mol of `XY_(2)= 10g`
0.1 mol of `XY_(2)=10g`
1.0 mol of `XY_(2)=10/0.1 xx 1.0 = 100 g`
or `x+2y = 100 g mol^(-1)` ………(i)
For `X_(3)Y_(2)` = 9g
1 mol `X_(3)Y_(2) = 9/0.05 = 180` g
or `3x + 2y = 180 g mol^(-1)`...........(ii)
Subtracting eq. (i) from (ii)
`2x = 80 g mol^(-1)` or `x= 40 g mol^(-1)`
and 40 + 2y = 100
or `y=(100-40)/2 = 30 g mol^(-1)`