An introduction to titration--why we use it, the advantage of water solution chemistry, and acid-base, conductimetric and redox titrations.

1. Titration
Using water solutions to
make analytical work
faster, easier and
more accurate
Mpcfaculty.net

2. Why Water Solutions?

Why do chemists prefer to conduct reactions in
water solution?
−
Water is a “universal solvent”
−
A true solution is homogeneous

−
Every mL solution mmoles = any other mL mmoles
Water is a non-conductor

No “noise” obscuring conductivity titrations
−
Water is the product of most acid-base reactions
−
Many interesting salts not soluble in water

Enables precipitation reactions

3. Types of Titration

Acid-base titration
−

Oxidation-reduction titration
−

Usually one or the other has a color change
Precipitation titration
−

Requires a weak acid indicator for equivalence pt.
Difficult: equivalence point hard to spot (no ppt)
Conductimetric titration
−
Relies on the different size of the ions reacted and
in excess

4. Acid-Base Titration


Indicator is one color at pH below the equivalence
point and changes color close to equivalence point.
Problem: Titrating an unknown molarity of HCl
(32.20 mL) with 0.0520 M NaOH reaches a color
change at 25.04 mL base. What is molarity of acid?
−
Strong acid and strong base—what is equiv pH?
−
Ma x Va = Mb x Vb so Ma = Mb x Vb
Va
Ma = (0.0520 M) x 25.04 mL = 0.0404 M acid
32.20 mL
−

5. Why Indicators Work If Chosen Properly

If the indicator's
pKa is close to the
equivalence pH,
then the rapid
change in pH
around the equiv pt
makes the indicator
change colors like a
stop light
Methyl orange changes colors just
short of the equivalence pH of 7 when
using strong acid and strong base
Titrations.info
So methyl orange would be a decent indicator if you
titrate base into acid. Would it work if you titrated acid
into base?

6. Why Indicators Work If Chosen Properly

If the indicator's
pKa is close to the
equivalence pH,
then the rapid
change in pH
around the equiv pt
makes the indicator
change colors like a
stop light
Methyl orange changes colors just
short of the equivalence pH of 7 when
using strong acid and strong base
Titrations.info
So methyl orange would be a decent indicator if you
titrate base into acid. Would it work if you titrated acid
into base?