1. 2.4 Prefixes and Equalities
Using a retinal camera, an ophthalmologist photographs the retina of the eye.
Learning Goal Use the numerical values of prefixes to write a metric equality.

2. Prefixes
A special feature of the SI as well as the metric system is that a prefix can be placed in front of any unit to increase or decrease its size by some factor of ten.
For example, the prefixes milli and micro are used to make the smaller units.
milligram (mg)
microgram (μg or mcg)
Core Chemistry Skill Using Prefixes

3. Metric and SI Prefixes
Prefixes That Increase the Size of the Unit

4. Metric and SI Prefixes
Prefixes That Increase Decrease the Size of the Unit

5. Prefixes and Equalities
The relationship of a prefix to a unit can be expressed by replacing the prefix with its numerical value.
For example, when the prefix kilo in kilometer is replaced with its value of 1000, we find that a kilometer is equal to 1000 meters.
kilometer = 1000 meters (103 m)
kiloliter = 1000 liters (103 L)
kilogram = 1000 grams (103 g)

6. Daily Values for Selected Nutrients
The U.S. Food and Drug Administration uses metric prefixes to express amounts of daily nutrient requirements.

7. Study Check
Fill in the blanks with the correct prefix: A m = 1 ___ m B. 1 × 10−3 g = 1 ___ g C m = 1 ___ m

8. Solution
Fill in the blanks with the correct prefix: A m = 1 ___ m The prefix for 1000 is kilo; 1000 m = 1 km. B. 1 × 10−3 g = 1 ___ g The prefix for 1 × 10−3 is milli; 1 × 10−3 g = 1 mg. C m = 1 ___ m The prefix for 0.01 is centi; 0.01 m = 1 cm.

9. Measuring Length
Ophthalmologists measure the diameter of the eye’s retina in centimeters (cm), while a surgeon measures the length of a nerve in millimeters (mm). Each of the following equalities describes the same length in a different unit. 1 m = 100 cm = 1 × 102 cm 1 m = 1000 mm = 1 × 103 mm 1 cm = 10 mm = 1 × 101 mm

10. Measuring Volume
Volumes of 1 L or smaller are common in the health sciences. When a liter is divided into 10 equal portions, each portion is called a deciliter (dL). Examples of some volume equalities include the following: 1 L = 10 dL = 1 × 101 dL 1 L = 1000 mL = 1 × 103 mL 1 dL = 100 mL = 1 × 102 mL

11. Measuring Volume

12. The Cubic Centimeter
The cubic centimeter (abbreviated as cm3 or cc) is the volume of a cube whose dimensions are 1 cm on each side. A cubic centimeter has the same volume as a milliliter, and the units are often used interchangeably. 1 cm3 = 1 cc = 1 mL and 1000 cm3 = 1000 mL = 1 L A plastic intravenous fluid container contains 1000 mL.

13. The Cubic Centimeter
A cube measuring 10 cm on each side has a volume of cm3.
10 cm × 10 cm × 10 cm = 1000 cm3 = 1000 mL = 1 L

14. Measuring Mass
When you visit the doctor for a physical examination, he or she records your mass in kilograms (kg) and laboratory results in micrograms (μg or mcg). Examples of equalities between different metric units of mass are as follows: 1 kg = 1000 g = 1 × 103 g 1 g = 1000 mg = 1 × 103 mg 1 g = 100 cg = 1 × 102 cg 1 mg = 1000 μg, 1000 mcg = 1 × 103 μg

15. Study Check
Identify the larger unit in each of the following: A. mm or cm B. kilogram or centigram C. mL or μL D. kL or mcL

16. Solution Identify the larger unit in each of the following:
mm or cm A millimeter is m, smaller than a centimeter, 0.01 m.
kilogram or centigram A kilogram is 1000 g, larger than a centigram, 0.01 g.
mL or μL A milliliter is L, larger than a microliter, L.
kL or mcL A kiloliter is 1000 L, larger than a microliter, L.