Chemical Calculations And Chemical Formulas Worksheets With Answer Key Page 7
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Chapter 9 – Chemical Calculations and Chemical Formulas
Exercise 9.8 - Calculating an Empirical Formula:
An ionic compound used in the
brewing industry to clean casks and vats and in the wine industry to kill undesirable yeasts and
bacteria is composed of 35.172% potassium, 28.846% sulfur, and 35.982% oxygen. What is the
empirical formula for this compound? (Obj 17)
1 mol K
? mol K = 35.172 g K
= 0.89958 mol K ÷ 0.89958 = 1 mol K × 2 = 2 mol K
39.0983 g K
1 mol S
? mol S = 28.846 g S
= 0.89958 mol S ÷ 0.89958 = 1 mol S × 2 = 2 mol S
32.066 g S
1 mol O
1
? mol O = 35.982 g O
= 2.2490 mol O ÷ 0.89958 2 mol O × 2 = 5 mol O
15.9994 g O
2
Empirical Formula K
S
O
2
2
5
Exercise 9.9 – Calculating a Molecular Formula Using the Percentage of Each
Element in a Compound: Compounds called polychlorinated biphenyls (PCBs) have
structures similar to chlorinated insecticides such as DDT. They have been used in the past for a
variety of purposes, but because they have been identified as serious pollutants, their only legal
use today is as insulating fluids in electrical transformers. This is a use for which no suitable
substitute has been found. One PCB is 39.94% carbon, 1.12% hydrogen, and 58.94% chlorine
and has a molecular mass of 360.88. What is its molecular formula? (Obj 19)
1 mol C
? mol C = 39.94 g C
= 3.325 mol C ÷ 1.11 = 3 mol C × 2 = 6 mol C
12.011 g C
1 mol H
? mol H = 1.12 g H
= 1.11 mol H ÷ 1.11 = 1 mol H × 2 = 2 mol H
1.00794 g H
1 mol Cl
1
? mol Cl = 58.94 g Cl
= 1.662 mol Cl ÷ 1.11 1 mol Cl × 2 = 3 mol Cl
35.4527 g Cl
2
molecular mass
360.88
Empirical Formula C
H
Cl
n =
=
2
6
2
3
empirical formula mass 180.440
Molecular Formula = (C
H
Cl
)
or
C
H
Cl
6
2
3
2
12
4
6
Review Questions Key
1. Complete each of the following conversion factors by filling in the blank on the top of the
ratio.
3
3
10
g
10
kg
a.
c.
1 kg
1 metric ton
3
6
10
mg
10
g
b.
d.
1 g
1 g
2. Convert 3.45 10
4
kg into grams.
3
10 g
= 3.45 10
7
4
? g = 3.45 × 10 kg
g
1 kg
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