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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
93
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 10
Example Problem 10-3
Converting Mass to Moles
A roll of copper wire has a mass of 848 g. How many moles of copper are in the roll? Use the atomic mass of copper given on the
periodic table to apply a conversion factor to the mass given in the
problem.
moles of Cu ϭ grams Cu ϫ
moles of Cu ϭ 848 g Cu ϫ
ϭ13.3 mol Cu
Note that the conversion factor is arranged so that g Cu cancel,
leaving only mol Cu, the desired quantity.
Example Problem 10-4
Converting Moles to Mass
Calculate the mass of 0.625 moles of calcium.
Use the molar mass of calcium to apply a conversion factor to the
number of moles given in the problem. According to the periodic
table, the atomic mass1 of calcium is 40.078 amu, so the molar mass
of calcium is 40.078 g.
mass of Ca ϭ mol Ca ϫ
mass of Ca ϭ 0.625 mol Ca ϫ
ϭ25.0 g Ca
The conversion factor is arranged so that mol Ca cancel, leaving
g Ca, the desired quantity.
Practice Problems
6. Calculate the mass of 6.89 mol antimony.
7. A chemist needs 0.0700 mol selenium for a reaction. What
mass of selenium should the chemist use?
8. A sample of sulfur has a mass of 223 g. How many moles of
sulfur are in the sample?
40.078 g Ca
ᎏᎏ
1 mol Ca
grams Ca
ᎏᎏ
1 mol ca
1 mol Cu
ᎏᎏ
63.546 g Cu
1 mol Cu
ᎏᎏ
grams Cu