The molecular masses of sulphate and hydroxide of a metal M are 142 and 40 respectively. Calculate atomic mass and valency of the metal.

Explanation

Let the valency of metal be x and atomic weight be m.
`:.` Metal sulphate is `M^(** **) SO_4^(2-) implies M_(2) (SO_4)_x`
`:. ` Metal hydroxide is `M^(** **) O overset(bar)(H_4^(-2)) = > M (OH)_x`
`:.` Molecular weight of metal sulphate is
` 2m + 96x = 142 to ` (1)
Molecular weight of metal hydroxide is m + 17x = 40
`implies 2m + 34x = 80 to` (2)
From (1) and (2)

`impliesx = 1`
`:.` From (1) `implies 2m + 96(1) =142`
`implies 2m = 142 - 96 = 46 implies m = 23 `
`:.` Valency and atomic weight of the metal are 1 and 23, respectively.