c. Example 2. What is the concentration of a solution that was prepared by
adding 75 mL of alcohol to 175 mL of water?
Solution. Read the problem carefully and determine the unknown quantity.
Solving this type of problem involves expressing the volume of solute per unit
Determine the total volume of solution.
175 mL water
75 mL alcohol
250 mL total volume
Since the unit volume is deciliters, convert the given volume in milliliters to
250.0 mL X -------- = 2.50 dL
To conclude solving the problem express the volume of solute per unit
volume and evaluate the numerical data as follows.
-------- = 30 mL/dL or equivalently, 30
2-31. WEIGHT/WEIGHT PERCENT SOLUTIONS
This type, weight/weight percent solutions (w/w), of percent solution is usually
expressed as (w/w), where "w" denotes weight (usually grams) in both cases. An
example of a correct designation for this type of solution is as follows: 10 g/100 g (w/w),
which indicates to the technician that there are 10 grams of solute for every 100 grams
total solution. The (w/w) denotes that the solution is a "weight in weight" percent
solution. This type of solution is rarely if ever prepared in the clinical laboratory since it
is easier to measure volumes of liquids rather than weigh the liquid on an analytical
balance. One must be familiar with w/w solutions because the common laboratory
acids and bases are manufactured on a weight-in-weight basis. For more discussion on
this, please refer to Lesson 8, Concentrated Acids and Bases.