First, let us consider the mol/L concentration. Note that mol/L times the gram

molecular weight (g/mol) yields g/L (mol/L X g/mol = g/L). Thus, g/L can also be

referred to as parts solute per 1000 total solution. And the g/dL concentration times 10

dL/1 L yields parts per 1000. Equivalently, the g/dL concentration times 10 equals the

molar concentration times the gram molecular weight.

a. **Example 1**. What is the molarity of a 4.0 g/dL NaCl solution?

Solution. Read the problem carefully and determine the desired unit of

concentration.

Molarity (mol/L).

Comparable to problems encountered before that involved molarity,

calculating the gram molecular weight is a good place to start.

NaCl

Na

23.0

Cl

+ 35.5

58.5 g/mol

Now that the number of grams per mole has been determined, use it as an

appropriate factor along with the conversion factor that will convert deciliters to liters.

4.0 g

1 mol

10 dL

------ X --------X ------ = 0.68 mol/L

dL

58.5 g

1L

b. **Example 2**. You are directed to prepare 500 mL of a 5.0 mol/L FeSO4

solution. What is the percent concentration of the solution?

Solution. Read the problem carefully and determine the desired unit of

concentration.

Percent concentration (%).

Calculate the GMW of the compound.

FeSO4

Fe 55.8 X 1 =

55.8

S 32.1 X 1 =

32.1

O 16.0 X 4 =

+ 64.0

151.9 g/mol

MD0837

5-3

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