Untitled - Kelly Walsh High School

Aqueous Solutions 73
Don’t Forget!
Quick Tip
of this step will use the definition of molarity, moles solute/ liters of solution.
For this problem, our setup will be:
(0.0500 L)a 0.100 mol HC2H3O2 ba
L
1 mol Ca(OH) 2
b
2 mol HC2H3O2 2.50 10 3 mol Ca(OH) 2
If the problem begins with milliliters instead of liters, you will need to convert
the milliliters to liters.
This calculation leaves us with the appropriate number of significant figures and
the correct units.
Molarity is a useful means of reporting concentrations. However, in most problems
concerning molarity, you should use the definition (mol/L) instead of M.
The first part of this problem appears in numerous problems involving solutions.
Moles are critical to all stoichiometry problems, so you will see this step
over and over again. This is so common, that anytime you see a volume and a
concentration of a solution, you should prepare to do this step.
Now let us try an example needing additional information after the mole ratio
step. How many grams of calcium hydroxide are necessary to titrate 0.200 mol of
acetic acid? As usual, we begin by adding this information to the balanced
chemical equation:
2 HC2H3O2(aq) Ca(OH) 2(aq) l Ca(C2H3O2) 2(aq) 2 H2O(l) 0.200 mol ? g