Weight/Volume Percent Solutions

percentage, which means parts per 100 total parts. This method is used with all three

of the basic comparisons of percent concentration statements, that is, weight/weight,

weight/volume, and volume/volume. The percent weight/weight is not commonly used

in the clinical laboratory.

2-27. WEIGHT/VOLUME PERCENT SOLUTIONS

a. The weight per unit volume system of percent concentration is the most

frequently used method in the clinical laboratory. This method is used when a solid

solute is mixed with a liquid solvent. Since percent is parts per 100 parts of total

solution, then a weight/volume percent solutions (w/v) unit would be grams of solute per

100 milliliters of total solution (g/100 mL). In the clinical laboratory and related

situations, any time a w/v solution is described by a number followed by a percent

symbol (grams per 100 mL (g/100 mL). Since 100 milliliters is equal to one deciliter,

then a percent w/v concentration can be expressed as grams per deciliter (g/dL).

b. Another expression of w/v percent concentration used in the laboratory

involves the use of fractional parts of the gram while retaining the unit of volume of

solution. Examples of this kind would be milligram per deciliter or milligram percent.

These may be expressed as mg/dL, mg/100 mL, or mg

c. The following problems may be solved using dimensional analysis (see

Appendix A); however, simple ratio and proportion will suffice in some instances. Both

methods of problem solving will yield comparable results.

d. Example. If a 5.0 g/dL solution of NaCl is to be prepared with a volume of

50 mL, how much NaCl would be required?

Solution. Based on definition the same problem could be solved using

appropriate factors.

By dimensional analysis, we would solve as follows:

After reading the problem carefully it should be quite evident that the desired

quantity is the amount of solute expressed in grams.

Express the volume in dL

1 dL

50. 0 mL X = -------- = 0.500 dL

100 mL

Multiply the volume expressed in deciliters times the percent concentration to

determine the amount of solute contained in the specified amount of total solution.

5.0 g

0.500 dL X = ------ = 2.5 g

MD0837

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