CHEMISTRY
CHAPTER 4
PROBLEM SOLVING IN CHEMISTRY
Steps for solving word problems:
1.
2.
3.
4.
5.
Find unknown
Find knowns
Plan solution
Calculate
Check
A conversion factor is a ratio with a
value of one.
Ex.
1 ft = 12 inches
1.00g water = 1 mL water
100 cm = 1m
Dimensional Analysis is also called
the “factor label method” of
problem solving.
Ex. 52.5 m = ____ mm
52.5 m x 1000 mm
1m
or
= 5.25 x 104 mm
52.5m 1000mm = 5.25 x 104 mm
1m
Ex. 73.2 km = ____ cm
73.2 km 1000m
1 km
73.2 km 1000m 100 cm
1 km
1m
= 7.32 x 106 cm
How many seconds are there in 2.5
years?
2.5 years 365 days
1 year
2.5 years 365 days
1 year
2.5 years 365 days
1 year
2.5 years 365 days
1 year
= 7.9 x 107 s
24 hours
1 day
24 hours
1 day
24 hours
1 day
60 min
1 hour
60 min 60 s
1 hour 1 min
A clock gains 0.25 seconds per minute. How
many seconds will it gain in exactly 180 days?
180 days 24 hr
1 day
180 days 24 hr
1 day
180 days 24 hr
1 day
60 min
1 hr
60 min 0.25s gained
1 hr
1 min
=6.48 x 104 s gained
= 6.5 x 104 s gained
A fictitious unit of length called the “zither” is defined by
the relationship 7.50 cm = 1.00 zither. How many zithers
are in a 100.0 meter distance?
100.0m 100cm
1m
100.0m 100cm 1.00 zither
1m
7.50 cm
= 1333 zithers
= 1330 zithers
What is the mass of a 35.0 mL sample of
concentrated sulfuric acid (density 1.84g/mL)?
35.0 mL 1.84g
1 mL
= 64.4 g
Nolan Ryan threw a fastball 100.8 mi/h. Calculate
this velocity in m/s. 1 mi = 1.6093 km.
100.8 mi
1h
100.8 mi 1.6093 km
1h
1 mi.
100.8 mi 1.6093 km 1000 m
1h
1 mi.
1 km
100.8 mi 1.6093 km 1000 m 1hr
1h
1 mi.
1 km 60 min
100.8 mi 1.6093 km 1000 m 1hr
1 min
1h
1 mi.
1 km 60 min 60 s
45.06 m/s
The density of copper is 8.96g/cm3 at 25oC.
Determine its density in kg/m3.
8.96g
1 cm3
8.96g 1kg
1 cm3 1000g
8.96g 1kg
(100)3cm3
1 cm3 1000g 1m3
=8960 kg/m3 or 8.96 x 103 kg/m3
Copper makes up 1.1 x 10-4 percent by mass of a normal
healthy human. How many grams of copper would be found
in the body of a person weighing 150 lb? (1.0 kg = 2.2 lb)
150 lb man 1.0kg man
2.2 lb man
150 lb man 1.0kg man 1000g man
2.2 lb man 1 kg man
150 lb man 1.0kg man 1000g man 1.1 x 10-4g Cu
2.2 lb man 1 kg man 100g man
= 7.5 x 10-2 g Cu or 0.075g Cu