Acids- Base
Titration and pH
Aqueous Solutions
and the Concept of
pH


When two molecules of water
produce a hydronium and
hydroxide ion by the transfer of
a proton.
H2O + H2O   H3O+ + OH-
At 25C the [H3O+] = [OH-]= 10-7 M
 So, the products of [H3O+] and [OH-] can be
represented by:
 [H3O+] x [OH-]
 10-7 M x 10-7 M = 10-14 M2
 Where 10-14 M2 Is the Kw ( ionization constant
of water)
So, [H3O+] x [OH-]= Kw at 25C

Neutral solutions:
[H3O+] = [OH-]= 10-7 M

Acidic solutions:
[H3O+] > [OH-]

Basic solutions:
[H3O+] < [OH-]

 We
can find the [H3O+]
and[OH-] by using the
formula:
 [H3O+] x [OH-]= Kw= 10-14 M2
Practice p: 484
It is the negative logarithm of the
hydronium ion concentration
pH= - log [H3O+]
 Likewise,
pOH It is the
negative logarithm of the
hydroxide ion
concentration
 pOH= - log [OH ]

 So, pH + p OH= 14 at 25 C
 [H3O+]=10-pH
Practice
p:
487


1- [H3O+] x [OH-]= Kw

2- pH= - log [H3O+]

3- pOH= - log [OH-]

4- pH + p OH= 14 at 25C

5- [H3O+]=10-pH
Determining pH
and Titrations
 1- Acid- Base indicators: are compounds
whose colors are sensitive to pH. Indicators
come in many different colors. The exact pH
range over which an indicator changes color
also varies.

2-Universal indicators: the pH of
solution can be determined by
comparing the color it turns with the
scale of paper.
3- pH meter: determines the pH of a solution by
measuring the voltage between the electrodes
that are placed in the solution. (It’s the most
accurate way to determine the pH)

Is the controlled addition and measurement of
the amount of a solution of known
concentration required to react completely with
a measured amount of a solution of unknown
concentration.
The equation of titration is:

H3O+ + OH-  2H2O

 1-
strong acid- strong base
 2-
strong acid- weak base
 3-
weak acid- strong base
Indicators are specific, each type of titration
needs a specific indicator
 For example:
 Strong acid- strong base titration:
We use bromothymol blue (6.2- 7.6)
 For strong acid- weak base titration:
We use bromophenol blue ( 3-4.6)
 For weak acid- strong base titration
We use phenolphtalein(8-10)

 The
point at which the two
solutions used in a titration
are present in chemically
equivalent amounts is
called the equivalence
point.
The
endpoint in
titration marks the
point at which the
color of indicator
changes.





The solution that contains precisely known
concentration of solute is known as the
standard solution.
To find the molarity or the volume of an
unknown solution we use the equation:
No of moles of acid= No of moles of base
CxV (acid)= CxV (base)
Practice p: 503 (1 and 2)