Weight/Volume Percent Solutions - Laboratory Mathematics

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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
dL
MD0837
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