Question

Cuprous sulphide and silver sulphide are isomorphous. The atomic mass of Cu is 63.57 g/mole. If the percentage composition of Sulphur in each of these is 20.14% and 12.94% respectively then the atomic mass of silver will be:
A. 208
B. 108
C. 112
D. 115

Answer 1

Correct Answer - B
Suppose the atomic weight of S and M are x and y respectively. Now, for `Cu_(2)S`
`1 xx` mole of `Cu = 2 xx` moles of S
`1 xx (0.7986)/(63.5) = 2xx (0.2014)/(x) -------gt (I)`
(1g of `Cu_(2)S` contains `0.786g` and `0.2014g` of Cu and S respectively. And for `M_(2)S`,
` 1xx (0.8706)/(y) = 2 xx (0.1294)/(x)` ---rarr (II)
(1g of `M_(2)S` constains `0.8706g` and `0.1294g` of M and S respectively from eqns. 1 and 2..
we get `y = 107.7`
`:.` atomic weight of M is `107.70`