Untitled - Kelly Walsh High School

Aqueous Solutions 71
Don’t Forget!
calculations for acid-base titrations are identical to those for any type of titration
reaction. The key to any titration calculation will be moles.
In an acid-base titration you may either add acid to base or base to acid. This
addition continues until there is some indication that the reaction is complete.
Often a chemical known as an indicator will indicate the endpoint of a titration
reaction, the experimental end of the titration. If we perform the experiment
well, the endpoint should closely match the equivalence point of the titration,
the theoretical end of the reaction. All the calculations in this section assume
accurate experimental determination of the endpoint, and that this value is the
same as the equivalence point.
We will work with the following acid-base titration reaction for the remainder
of this section:
2 HC 2H 3O 2(aq) Ca(OH) 2(aq) l Ca(C 2H 3O 2) 2(aq) 2 H 2O(l)
For example, we could use this reaction for determining the concentration of
acetic acid, HC 2H 3O 2, in vinegar. A titration problem will give you information
about one reactant, and ask you for information about the other reactant. In most
titration reactions, information about the products will not be necessary. You only
need to consider the products when we need to balance the chemical equation.
If we want to use the concentration of acetic acid to find the concentration of
calcium hydroxide, we will need this step (the numbers are the coefficients in
the balanced chemical equation):
a 1 mol Ca(OH) 2
b
2 mol HC2H3O2 If we want to use the calcium hydroxide to find out about the acetic acid, we will
need this step:
a 2 mol HC2H3O2 b
1 mol Ca(OH) 2
In titration calculations, you must consider the reaction stoichiometry.