Question

1/ After 0.62 g of CoCl2⋅6H2O is heated, the residue has a mass of 0.321 g . Calculate the % H2O in the hydrate.

2/What was the actual number of moles of water per formula unit CoCl2Provide two significant figures in your answer.

Answer 1

1 Ans.

Mass of the residue before heating = 0.62g

Mass of the residue after heating = 0.321g

Therefore, mass of water is given by

% of hydrate is

%

Therefore, percent of hydrate is 48%

2 Ans.

Mass of H₂O = 0.299g

Molar mass of H₂O = 18.015g/mol

No. of mol of H₂O is

(No. of mol of H₂O should have two significant figures but it is not yet rounded off)

Molar mass of CoCl₂ = 129.839g/mol

Divide the no. of mols by the no. of mol of CoCl₂

For H₂O, 0.0166 divided 0.00247 = 6.7

For CoCl₂, 0.00247 divided by 0.00247 = 1

Therefore, per unit mol of CoCl₂, there are 6.7 mol of H₂O.