1. Writing Conversion Factors
General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 1
Chemistry and Measurements
1.8
Writing Conversion Factors
Lectures
© 2013 Pearson Education, Inc.

2. Equalities Equalities
use two different units to describe the same measured amount.
are written for relationships between units of the metric system; between U.S. units or between metric and U.S. units.
Examples:

3. Equalities and Conversion Factors
Equalities are
written as a fraction.
used as conversion factors.
can be represented with one equality in the numerator and the second equality in the denominator.
Examples:

4. Common Equalities

5. Exact and Measured Numbers in Equalities
Equalities between units of
the same system are definitions with numbers that are exact.
different systems (metric and U.S.) are measurements with numbers that have significant figures.
The equality of 2.54 cm = 1 in. is an exception and considered to be exact.

6. Metric Conversion Factors
We can write equalities as conversion factors.

7. Metric-US Conversion Factors
Metric–US conversion factors are written as a ratio with
a numerator and denominator.
Example:

8. Equalities on Food Labels
The contents of packaged foods
in the U.S. are listed in both metric and U.S. units.
indicate the same amount of a substance in two different units.

9. Learning Check
Write equalities and conversion factors for each pair of units.
1. liters and mL
2. hours and minutes
3. meters and kilometers

10. Solution Write equalities and conversion factors for each pair
of units.

11. Conversion Factors in a Problem
A conversion factor
may be obtained from information in a word problem.
is written for that problem only.
Example 1: The motorcycle was traveling at a speed of
85 km/h.
Example 2: One tablet contains 500 mg vitamin C.

12. Percent as a Conversion Factor
A percent factor
uses a ratio of the parts to the whole in a fraction.
uses the same units for the parts and whole.
uses the value 100 for the whole.
can be written as two factors.
Example: A food contains 18% (by mass) fat.

13. Parts per Million, Parts per Billion
Parts per Million, ppm is the same as mg per kilogram mg/kg of substance.
Parts per Billion, ppb is the same as g per kilogram g/kg of substance.
Example: The maximum dose of lead in pottery glaze is 2 ppm.

14. Chemistry Link to Health
Toxicology and Risk-Benefit Assessment
One measure of toxicity is the LD50 or lethal dose,
which is the concentration of the substance that
causes death in 50% of the test animals.
A dose is typically measured in ppm (mg/kg) of body
mass or ppb (μg/kg).

15. Chemistry Link to Health
Toxicology and Risk-Benefit Assessment

16. Learning Check
Write the equality and conversion factors for each of the following.
1. meters and centimeters
2. jewelry that contains 18% gold
3. one liter of gas is $ 0.95

17. Solution
Write the equality and conversion factors for each of the following.