e. Examining the solution reveals that the given volume in milliters is first

converted to deciliters, using the appropriate conversion factor. The volume of solution

expressed in deciliters is then multiplied by the weight per volume concentration to yield

the desired quantity, mass of solute expressed in grams per given volume. Notice that

if the correct factor is used the unwanted units cancel out.

The first step in solving any solution problem is to carefully read the problem.

Remember that a unit of concentration consists of two components-- a weight (or

volume) and a volume, thus w/v or v/v. Also notice that in reading the problem, the

wording will suggest that a solution is to be prepared. Words such as "prepare" or

"make" will be used in this type of problem. When making a percent solution, three

things are necessary, that is, mass of solute needed, concentration of the solution to be

prepared, and total volume of solution. Consider and see that all three of these

requirements are met. Mass of solute is usually expressed in grams or milligrams.

Concentration of the solution in g/dL, mg/dL, or (mL/dL). Total volume of solution is

expressed in deciliters. Use the information given in the problem or calculated from

information given in the problem as appropriate factors.

a. **Example 1**. How much NaCl is needed to make 2.0 liters of a 3.0 g/dL NaCl

solution?

Solution. The first step of any problem is to read the problem carefully.

Determine what the problem is asking for.

Grams of solute (NaCl).

Express the volume in deciliters.

10 dL

2.0 L X -------- = 20 dL

1L

Multiply the volume expressed in deciliters times the percent concentration to

determine the grams of NaCl contained in 2.0 liters of a 3.0 g/dL solution.

3.0 g

20 dL X -------- = 60 g

dL

MD0837

2-9

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