Question

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

Answer 1

Correct Answer - A
Let atomic masses if x and Y be `A_(X)and A_(Y)`, respectively
For `XY_(2), n_(XY_(2))=0.1=(10)/(A_(X)+2A_(Y))`
or `A_(X)+2A=100` . . . (i)
For `X_(3)Y_(2),n_(X_(3)Y_(2))=0.05=(9)/(3A_(X)+2A_(Y))`
or `3A_(X)+2A_(Y)=180` . . .(ii)
On solving Eqs. (i) and (ii) , we get,
`A_(X)=40 g "mol"^(-1)`
`rArrA_(Y)=30 g "mol"^(-1)`