Solution. Read the problem carefully and determine the desired quantity.
Grams of CuSO4.H2O.
Calculate the amount of the anhydrous form needed.
1 dL
10.0 g
100 mL X -------- X -------- = 10.0 g
100 mL
1 dL
Calculate the gram molecular weight of each substance. (NOTE: You will
learn more about gram molecular weights and moles in Lesson 3.)
(1)
List each element in a column.
(2)
Write the atomic weight of each element. (See Appendix C.)
(3) Multiply the weight of each element by the number of that element in the
chemical formula. For example, if there are 2 atoms of hydrogen present in the formula,
multiply the weight of hydrogen by two.
(4) Sum the weights to obtain the total weight, and express the total weight
in grams/mole.
CuSO4 (anhydrous)
Cu 63.5 X 1 = 63.5
S
32.1 X 1 = 32.1
O 6.0 X 4 = + 64.0
159.6 g/mole
CuSO4.H2O (hydrate)
Cu
63.5 X 1 = 63.5
S
32.1 X 1 = 32.1
O
6.0 X 4 = 64.0
H
1.0 X 2 = 2.0
O
6.0 X 1 = + 16.0
177.6 g/mol
If the amount of anhydrous salt needed is now multiplied by the ratio of the
molecular weights of the hydrate to anhydrate the desired results will be obtained.
177.6 g/mol CuSO4.H2O
10.0 g CuSO4 X ---------------------- = 11.1 g CuSO4.H2O
159.6 g/mol CuSO4
MD0837
2-12
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