Percentage of Water in a Hydrate / Formula of a Hydrate


a.       To find the % of water in crystallized copper (II) sulfate.

b.      To determine the formula of the hydrate


Many salts when crystallized from water solution take up definite proportions of water as an integral part of their crystal structures.  This water of hydration may be driven off by the application of heat.  The number of moles of water driven off per mole of the anhydrous salt is some simple number.  If the formula of the anhydrous salt is known you can determine the formula of the hydrate.



1)      Support a evaporating dish and cover with a watch glass on a wire gauze.  Heat for ~3 minutes to dry, and mass to the nearest 0.01 grams

2)      Add aprox. 5 grams of crystallized copper (II) sulfate to the dish and weigh to the nearest 0.01 grams

3)      Heat the dish and contents gently for 2 minutes.  Then increase heat gradually for 2 more minutes.

4)      Cool and weigh the dish and contents to the nearest 0.01 grams.

5)      Heat the dish and contents for another 2 minutes and reweigh.  Make sure weights are constant, if not reheat again until they are.

6)      Before discarding the product add a small amount of water and note the result to the product in the dish.


Data: (show all calculations in lab book)

1)      Weight of empty evaporating dish and watch glass                        _______________

2)      Weight of empty dish, glass,

and crystallized copper (II) sulfate                                                _______________

3)      Weight of crystallized copper (II) sulfate                           _______________

4)      Weight of dish, glass, and anhydrous copper (II) sulfate   _______________

5)      Weight of anhydrous copper sulfate                                   _______________

6)      Weight of water lost by heating                                           _______________

7)      % of water in crystallized copper (II) sulfate (exp)              _______________

8)      Moles of anhydrous copper sulfate                                     _______________

9)      Moles of water lost by heating                                             _______________

10)  Ratio of moles anhydrous copper (II) sulfate to water lost  _______________

11)  Formula of crystallized copper (II) sulfate                         _______________

12)  % of water by mass in your formula for

       copper (II) sulfate (theo)                                                   _______________

13)  % error                                                                              _______________


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