Question

An unknown hydrate of cobalt (ll) sulfate, CoSO₄ * XH₂O, is determined to be 10.4 % water. What is the chemical formula of the hydrate?

Answer 1

ANSWER:

Molecular formula of an unknown hydrate of cobalt (ll) sulfate = CoSO₄.XH₂O

Molecular mass of H₂O = 18.015 g/mol

Molecular mass of unknown hydrate of cobalt (ll) sulfate = (154.996 + 18.015X) g/mol

Mass % = 10.4 %

Now,

Mass % = (Molecular mass of H₂O x 100)/(Molecular mass of unknown hydrate of cobalt (ll) sulfate)

10.4 % = (18.015 g/mol x 100)/({154.996 + 18.015X} g/mol)

{154.996 + 18.015X} g/mol = (18.015 g/mol x 100)/(10.4)

{154.996 + 18.015X} g/mol = 173.221 g/mol

18.015X = 18.225

X 1

So, number of hydrate molecule is one.

Hence, the chemical formula of unknown hydrate of cobalt(II) sulfate is CoSO₄*1H₂O.