A solution of a salt of a metal was electrolysed for 150 minutes by passing 0.15 A current. The weight of the metal deposited was 0.783 g. The specific heat of the metal is `0.057" cal"//gK`. The atomic mass X of the metal is :

Options

A. `111.80" g"//mol`
B. `52.2" g"//mol`
C. `200" g"//mol`
D. `250" g"//mol`

Answer

A

Explanation

(a) According to Dulong & Petits Law,
Approximate Atomic mass`=(6.4" Cal"//K)/(0.057"Cal"//gK)=112.28" g"`
Quantity of charge passed
`=(0.5" amp")xx(150xx60 s)`
`=1350" amp"-s=1350" C"`
1350 C charge deposit metal =0.738 g
96500 C charge deposit metal
`=((0.738g))/((1350c))xx(96500c)=55.9 g`
`:.` Equivalent mass of metal=55.97 g
Approximate valency`=("App.Atomic mass")/("Equivalent mass")`
`=((112.28g))/((55.97 g))=2.006`
Since valency is a whole number,
Exact valency =2
Exact atomic mass`="Eq.mass"xx"valency"`
`55.97xx2=111.94 g`