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.

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

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

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

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)

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

Study Check Fill in the blanks with the correct prefix: A. 1000 m = 1 ___ m B. 1 × 10−3 g = 1 ___ g C. 0.01 m = 1 ___ m

Solution Fill in the blanks with the correct prefix: A. 1000 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. 0.01 m = 1 ___ m The prefix for 0.01 is centi; 0.01 m = 1 cm.

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

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

Measuring Volume

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.

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

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

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

Solution Identify the larger unit in each of the following: mm or cm A millimeter is 0.001 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 0.001 L, larger than a microliter, 0.000 001 L. kL or mcL A kiloliter is 1000 L, larger than a microliter, 0.000 001 L.