Percentage of Water in a Hydrate / Formula of a Hydrate

Purpose:

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

b. To determine the formula of the hydrate


Introduction:

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.

Procedure:

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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