8.7 ACID-BASE TITRATION
Titration involves the precise addition of solution in a ________ into a _________ volume of a
sample solution
Sample
Titrant
Standard
Solution
Primary
Standard
Endpoint
The solution being analyzed in a titration (usually in an Erlenmeyer Flask) – The
_____________ is known, but the _____________________ is usually unknown.
The solution in a burette during a titration; concentration is _____________
The titrant is added to the _________. The volume of titrant needed to neutralize the
sample is recorded and used to calculate the ______________ of the sample.
The solution whose concentration is known accurately and precisely
A pure and stable chemical used to determine the __________________ of acids or bases
The point in the titration when there is a sudden change in the _______________ from a
significant change in _____. Phenolphthalein indicator is often used and is usually
___________________ in acidic solutions and __________ in basic solutions. Indicators are
solutions of _________ acids or bases that change colours at certain pH.
Equivalence The point in the titration where _______________ has actually occurred; This is also the
point in which all the reactant in the sample is consumed.
Point
Titration Type #1  Strong Acid with Strong Base
Equivalence point: pH = _____ (i.e. the titration is complete
when the pH of the resulting solution equals ______. Therefore,
the chosen indicator should turn colour (i.e. reach its endpoint) at
a pH of ____.
Example 1: Calculate the volume of titrant needed to reach the
equivalence point in the titration of a 25.0 mL sample of 0.50
mol/L NaOH(aq) by 0.10 mol/L HCl(aq).
Step 1: Determine the amount of OH- in the sample before the
titration
Step 2: Determine the volume of acid needed to react with all the base in the sample.
Example 2: In a titration, a 25.00 mL sample of 0.350 mol/L hydrochloric acid is titrated with
standardized 0.500 mol/L sodium hydroxide solution. Determine the amount of unreacted
hydrogen ions and the pH of the sample after 5.00 mL of NaOH(aq) jas been added.
Titration Type #2  Weak Acid with Strong Base
Equivalence point: pH ___ 7.0
When performing calculations involving weak acids and strong bases, assume that although the acid
is weak, it reacts completely with the hydroxide ions. At the equivalence point, all the acid in the
flask has reacted.
Example 3: A 25.00 mL sample of a weak acid, hypochlorous acid, HClO(aq) is titrated with 0.100
mol/L potassium hydroxide, KOH(aq). The equivalence point is reached when 19.3 mL of the base
has been added. Determine the concentration of the acid and the pH at the equivalence point.
Titration Type #3  Strong Acid with Weak Base
Equivalence point: pH___ 7.0
 Before the titration begins, calculate the pH of the sample using the Kb of the weak base.
 At the equivalence point, H+ ions in the solution are the result of hydrolysis caused by the
conjugate acid of the weak base. Calculate the pH using the Ka of the conjugate acid. The
solution will be acidic and the pH < 7
 Beyond the equivalence point, determine the PH of the solution by the amount of excess
strong acid provided by the titrant. Determine the pH from the H+ produced by the
ionization of the strong acid.
Titration Curves of Different Types of Acids and Bases
Strong Acid and Strong Base
Strong Acid and Weak Base
Weak Acid and Strong Base
Choosing an Appropriate Indicator
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

When selecting an indicator for a titration, the
endpoint and equivalence point should be as close to
each other as possible, so we know the approx.
point that the equivalence point is reached
Acid-Base indicators are weak acids (HIn) – They
have one colour in their acid form and one colour in
their conjugate base form. The Ka values of these
indicators should be low to signify a weak acid
Strong Acid-Strong Base Titrations (Acid Sample and
Base Titrant OR Base Sample and Acid Titrant) –
Rapid change in pH around the equivalence point