Acid-Base Reactions
•
If we mix a strong acid solution with a strong base solution
• we get a neutral solution that is neither acidic nor basic.
•
For example:
• HCl + NaOH → NaCl + H
2
O
•
H
2
SO
4
+ 2 KOH → K
2
SO
4
+ 2 H
2
O

Acid-Base Reactions
•
Mixing a strong acid with a strong base gives us
water
a salt
• the conjugate base of the acid plus the conjugate acid of the base
•
In this case, a salt is an ionic compound of any kind.

Acid-Base Reactions
•
In most cases, the net ionic equation of a neutralization reaction is:
•
H
3
O + + OH → 2 H
2
O
•
The salt that is formed usually stays in solution.
•
The salt ions are spectator ions.

Titration
•
Acids and bases combine in different ratios:
•
1:1
• HCl + NaOH → NaCl + H
2
O
•
1:2
•
H
2
SO
4
+ 2 KOH → K
2
SO
4
+ 2 H
2
O
•
2:1
•
2 HCl + Ca(OH)
2
→ CaCl
2
+ 2 H
2
O

Titration
•
The point where the number of mols of hydronium ions equals the number of mols of hydroxide ions is called the equivalence point .
•
The stoichiometric ratio of the acid to the base in the balanced equation tells us where the equivalence point is.

Titration
Example 1:
How many mols of sulfuric acid are required to neutralize 0.50 mols of sodium hydroxide?
n
NaOH
= 0.50 mol
H
2
SO
4
+ 2 NaOH → Na
2
SO
4
+ 2 H
2
O n n
NaOH
H
2
SO
4
=
2
1
➙ n
H
2
SO
4
=
1 ×n
NaOH
2
=
0.50 mol
2 n
H
2
SO
4
= 0.25 mol

Titration
•
A titration is a neutralization reaction under controlled conditions.
•
We control the amounts of acid and base reacted while monitoring the pH of the reaction solution.
•
When we reach neutralization (the equivalence point), we carefully measure the amounts of the acid and the base.

Titration
•
A titration uses
• a flask or beaker to hold the unknown solution
• a burette to hold the known
(standardized) solution
• an indicator (added to the flask) to show the end of the titration.

Titration
•
The burette shows the volume of titrant added to the flask.
•
We read the meniscus to find the amount added.
•
Placing a white sheet with a black section below the meniscus can help to define the meniscus.

Titration
•
We can use an indicator to show the equivalence point (end point) of the titration.
•
We can also use a pH meter to find the end point by generating a pH curve.

Titration
•
On the left, a strong base is added to a strong acid.
•
The equivalence point occurs at pH
= 7 .

Titration
•
On the right, a strong acid is added to a strong base.
•
The equivalence point also occurs at pH = 7 .

Titration
Example 2:
A 25-mL solution of H
2
SO
4 is completely neutralized by 18 mL of 1.0 M NaOH. What is the concentration of the
H
2
SO
4 solution?
M
NaOH
= 1.0 M V
NaOH
= 18 mL = 0.018 L
M
H2SO4
= ? M V
H2SO4
= 25 mL = 0.025 L
H
2
SO
4
+ 2 NaOH → Na
2
SO
4
+ 2 H
2
O n
NaOH
= M
NaOH
V
NaOH
= (1.0)(0.018) mol = 0.018 mol n
NaOH n
H
2
SO
4
=
2
1
➙ n
H2SO4
= n
NaOH
2
=
0.018 mol
2
= 0.0090 mol n
H2SO4
M
H2SO4
=
V
H2SO4
=
0.0090 mol
0.025 L
= 0.36 M