Question

A chemist is given a sample of the CuSO4 hydrate and asked to determine the empirical formula of it. The original sample weighed 42.75 g and after heating the sample weighed 27.38 what is the formula

Answer 1

let there be X H2O , formula is CuSO4.XH2O

mass of it = 42.75

after heating the water is lost , hence X H2O is lost

water lost = 42.75-27.38 = 15.37 g

molar mass of H2O is 18.015 g/mol

X ( 18.015) = 15.37

X = 0.8532 moles

now CuSO4 mass = 27.38 g ,

CuSO4 moles = 27.38 / 159.6 = 0.17155            ( where 159.6 g/mol is molar mass of CuSO4)

now ratio of H2O moles/ CuSO4 moels = 0.8532/0.17155 = 5

hence emperical formula is CuSO4.5H2O