Keep in mind that moles are not an expression of concentration. The unit
mole is an expression of mass indicating the number of gram molecular
weights. Take caution not to confuse mole with molarity (mol/L). When
reporting moles, write the word moles, DO NOT abbreviate by using an M!!
Section II. MOLARITY AND MOLAR SOLUTIONS
Molarity (mol/L) is defined as the number of moles of a substance per liter of
SOLVING MOLARITY PROBLEMS
a. Example 1. How much Na 4 is needed to make 300 mL of a 2.00 mol/L
Solution. Notice in this problem that the wording suggests that a solution is to
be prepared. If you examine the problem, you should find that the type of solution to be
prepared is a molar solution. Read the problem carefully and determine the unknown
Grams of Na2SO4.
Regardless of the type, most molarity problems require the gram molecular
weight, so calculating the gram molecular weight is a good starting point.
23.0 X 2 = 46.0
32.1 X 1 = 32.1
16.0 X 4 = + 64.0
Express the desired volume in liters.
300 mL X ---------- = 0.300 L
Multiply the volume expressed in liters times the molar concentration times
the gram molecular weight to determine the amount of salt, in grams, needed to prepare
0.300 L X --------X ----------= 85.3 g