On dissolving 2.0g of metal in sulphuric acid. 4.51g of the metal sulphate was formed. The specific heat of the metal is 0.057 cal `g^(-1)`. What is the valency of the metal and exact atomic mass?

Explanation

Equivalent mass of `SO_(4)^(2-)` radical
`=("Ionic mass")/("Valency")=(96)/(2)=48`
Mass of metal sulphate =4.51 g ltbr. Mass of metal =2.0g
Mass of sulphate radical =(4.51-2.0)=2.51g
2.51 g of sulphate combine with 2.0g of metal.
So, 48 g of sulphate will combine with
`(2)/(2.51)=48=38.24g` metal
Equivalent mass of metal =38.24
According to Dulong and Petit's law,
Approximate atomic mass `=(6.4)/("specific heat")=(6.4)/(0.057)=112.5`
`"Valency"=("Approximately atomic mass")/("Equivalent mass")`
`=(112.5)/(38.24)=2.9=3`
Exact atomic mass `=38.24xx3=114.72`.