Question

A chemist is given a sample of the CuSO4 hydrate and asked to determine its the empirical formula. The original sample weighed 42.75 g. After heating to remove the waters of hydration, the sample weighed 27.38 g. Determine the formula for this hydrate.

Answer 1

Answer: The formula for this hydrate is $CuSO_4.5H_2O$

Explanation:

Decomposition of hydrated copper sulphate is given by:

$CuSO_4.xH_2O\rightarrow CuSO_4+xH_2O$

Molar mass of $CuSO_4$ = 160 g/mol

According to stoichiometry:

(160+18x) g of $CuSO_4.xH_2O$ decomposes to give 160 g of anhydrous $CuSO_4$

Thus 42.75  g of $CuSO_4.xH_2O$ decomposes to give=$\frac{160}{160+18x}\times 42.75$g of anhydrous $CuSO_4$

$\frac{160}{160+18x}\times 42.75=27.38$

$x=5$

Thus the formula for this hydrate is $CuSO_4.5H_2O$