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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
99
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 10
moles of Mn (in 100 g) ϭ 38.43 g Mn ϫ
ϭ
0.6995 mol Mn
By following the same pattern, the number of moles of carbon and
oxygen per 100-g sample may be calculated.
moles of C (in 100 g) ϭ 16.80 g C ϫ
ϭ1.399 mol C
moles of O (in 100 g) ϭ 44.77 g O ϫ
ϭ2.798 mol O
The results show the following relationship.
mol Mn : mol C : mol O ϭ 0.6995 : 1.339 : 2.798
To obtain the simplest whole-number ratio of moles, divide each
number of moles by the smallest number of moles.
moles of Mn ϭ
ϭ 1 mol Mn
moles of C ϭ
ϭ2 mol C
moles of O ϭ
ϭ4 mol O
The empirical formula for the compound is MnC 2 O 4 .
Practice Problems
26. The composition of acetic acid is 40.00% carbon, 6.71% hydrogen, and 53.29% oxygen. Calculate the empirical formula for
acetic acid.
27. An unknown compound is analyzed and found to be composed
of 14.79% nitrogen, 50.68% oxygen, and 34.53% zinc.
Calculate the empirical formula for the compound.
28. Calculate the empirical formula for a compound whose analysis
is 74.97% aluminum and 25.03% carbon.
29. The composition of ascorbic acid (vitamin C) is 40.92% carbon, 4.58% hydrogen, and 54.50% oxygen. What is the
empirical formula for vitamin C?
2.798 mol O
ᎏᎏ
0.6995
1.399 mol C
ᎏᎏ
0.6995
0.6995 mol Mn
ᎏᎏ
0.6995
1 mol O
ᎏᎏ
15.999 g O
1 mol C
ᎏᎏ
12.011 g C
1 mol Mn
ᎏᎏ
54.938 g Mn