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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
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