Cobalt (ii) nitrate (co(no3)2) exists as a hydrate with the composition of 37.1% water and 62.9% cobalt nitrate by mass. determine the molecular formula for this hydrate.

Co(NO₃)₂·6H₂O

Explanation:

Assume that you have 100 g of the hydrate.

Then you have 62.9 g Co(NO₃)₂ and 37.1 g H₂O.

1. You will need a chemical equation with masses and molar masses, so let’s gather all the information in one place.

:                                           182.94      18.02

                 Co(NO₃)₂·xH₂O ⟶ Co(NO₃)₂ + xH₂O

Mass/g:                                         62.9          37.1

2. Use the molar masses of each compound to calculate its number of moles.

3. Calculate the molar ratio of the two products.

Divide each number by the smaller number of moles (0.3438 mol).

4. Round off each number to the closest integer.

1 mol of Co(NO₃)₂ combines with 6 mol H₂O, so x = 6.

The formula of the hydrate is Co(NO₃)₂·6H₂O.

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