One gram of the chloride of an element was found to contain 0.835 g chlorine. Its vapour density is  85. Find its at. wt.

Wt. of chlorine=0.835g ; wt. of element =1.0−0.835=0.165g V.D = 85; Mol. wt. = 2 x V.D. = 2 x 85 = 170. We know:  Wt. of metal  Wt. of chlorine = Eq. wt. of metal  Eq. wt. of chlorine ; 0.165g0.835g=E35.5∴ E=0.1650.835×35.5=7.02Also, Mol. wt. (given) = Mol. wt. of MClx where x = Valency of  M170=(E×x)+(35.5×x)=7x+35.5x=42.5x∴ x=17042.5=4= Valency . ∴Exact at. wt. = Eq. wt.×Valency =7.02×4=28.08