Titration of a Strong Acid by a Strong Base Consider what happens to the pH of 25 mL of 02 M HCl as it is titrated with 25 mL of 02 M NaOH This result is shown in the diagram to the right The diagram is referred to as a ID: 511044
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Slide1
TitrationSlide2
Titration of a Strong Acid by a Strong Base
Consider what happens to the pH of 25 mL of 0.2 M
HCl
as it is titrated with 25 mL of 0.2 M
NaOH. This result is shown in the diagram to the right. The diagram is referred to as a ___________________ _____________. As you add base, [H+] ____________ and pH ___________ until what happens?Slide3
Ex
#1: The following quantities of 0.100 M
NaOH have been added to 50.0 mL of 0.100 M HCl
. Calculate the pH of the resulting solutions.
49.00 mL
50.00 mL
50.10
mL
51.00 mL
Titration of a Strong Acid by a Strong BaseSlide4
49.00
mL
50.00 mL
50.10 mL 51.00 mL
Because the pH change for strong/strong titrations is large near the equivalence point, the indicator need not change color at exactly pH = 7. Phenolphthalein is often the choice for strong/strong titrations. Its color change occurs during a pH change of 8.3 to 10, but just a slight excess (a few drops) of the titrant will cause this change.
Titration of a Strong Acid by a Strong Base
Ex #1:
The following quantities of 0.100 M NaOH have been added to 50.0 mL of 0.100 M HCl. Calculate the pH of the resulting solutions.Slide5
Titration of a Weak Acid with a Strong
Base
Calculating the pH of the weak acid depends on where you are in the titration process.
HC
2
H
3
O
2
+ Na
+
+ OH
-
Na
+
+ C
2
H
3
O2- + H2O
Titration ProcessBefore the titration startsBefore the equivalence point is reachedAt the equivalence pointAfter the equivalence point has been reached
HC
2
H
3O2
NaOH
Consider the titration of acetic acid with sodium hydroxide. Slide6
Titration of a Weak Acid with a Strong
Base
Titration Process
Before the titration starts
HC
2
H
3
O
2
NaOH
Consider the titration of acetic acid with sodium hydroxide.
Initially
,
we just consider the
acetic
acid before any base is added. To calculate the pH, follow the same process as calculating the pH of a weak acid.
Calculating the pH of the weak acid depends on where you are in the titration process.
HC
2
H
3
O
2
↔
C
2
H
3
O2-
+ H
2
OSlide7
Titration of a Weak Acid with a Strong
Base
Titration Process
2) Before
the equivalence point is
reached
HC
2
H
3
O
2
NaOH
Consider the titration of acetic acid with sodium hydroxide.
Think about what
species are present so that we approach the problem from the correct perspective.
The equation shows that since both HC
2
H
3
O
2
and C
2
H
3
O
2
--
are present, this becomes a _______ problem
.
Calculating the pH of the weak acid depends on where you are in the titration process.
HC
2
H
3
O
2
↔
C
2
H
3
O
2
-
+ H
2
OSlide8
Titration of a Weak Acid with a Strong
Base
Titration Process
3) At
the equivalence
point
HC
2
H
3
O
2
NaOH
Consider the titration of acetic acid with sodium hydroxide.
At
the equivalence point, for a strong acid with a strong base, the pH = ______. This is
not
the case for a weak acid problem. Why
?
Calculating the pH of the weak acid depends on where you are in the titration process.
HC
2
H
3
O
2
+ Na
+
+ OH
-
Na+ + C
2
H
3
O
2
-
+ H
2
OSlide9
Titration of a Weak Acid with a Strong
Base
Titration Process
After
the equivalence point has been
reached
HC
2
H
3
O
2
NaOH
Consider the titration of acetic acid with sodium hydroxide.
After
the equivalence point has been reached, the additional OH
--
has nothing left to react with so the pH is determined
by __________________________________.
Calculating the pH of the weak acid depends on where you are in the titration process.Slide10
Titration of a Weak Acid with a Strong
Base
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.
Since the molarities are equal and the acid is
monoprotic
, we will need _______ mL of
NaOH
to reach the equivalence point.
Why
is it important to realize this before we begin the problem?
25Slide11
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide12
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
Initially
,
we just consider the
acetic
acid before any base is added. To calculate the pH, follow the same process as calculating the pH of a weak acid.
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide13
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2H3O2
] ↔[H+]
[
C2H3O2
-]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide14
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide15
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide16
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide17
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide18
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide19
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide20
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide21
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide22
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide23
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide24
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide25
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide26
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide27
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide28
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide29
Titration of a Weak Acid with a Strong
Base
1) What
is the pH before titration?
HC
2
H
3
O
2
↔
H
+
+
C
2
H
3
O
2
-
R
[
HC
2
H3O
2] ↔
[
H+
]
[
C
2
H
3
O
2
-
]
I
0.2
0
0
C
-x
+x
+x
E
0.2-x
x
x
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide30
2)
What is the pH after 10.00 mL of the base has been added?
Titration of a Weak Acid with a Strong
Base
Think about what
species are present so that we approach the problem from the correct perspective.
The equation shows that since both HC
2
H
3
O
2
and C
2
H
3
O
2
--
are present, this becomes a _______ problem
.
HC
2H3O
2 ↔ C2H3
O2-
+ H2O
Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M
NaOH.Slide31
2)
What is the pH after 10.00 mL of the base has been added?
Titration of a Weak Acid with a Strong
Base
HC
2
H
3
O
2
↔
C
2
H
3
O
2
-
+ H
2
O
Ex. 25.0mL of 0.200 M HC2H3O2 is titrated with 0.200 M
NaOH.
R
HC2H
3O2
O
H-
H
2
O
C
2
H
3
O
2
-
I
(0.2M)(25x10
-3
L)
=0.005
(0.2M)(10x10
-3
L)
=0.002
0
C
- 0.002
- 0.002
+ 0.002
Final
0.003
0
0.002
HC
2
H
3
O
2
+ OH
-
C
2
H
3
O
2
-
+ H
2
O
R
[
HC
2
H
3
O
2
]
↔
[
H
+
]
[
C
2
H
3
O
2
-
]
I
0.003mol/35x10
-3
L
=0.0857 M
0
0.002mol/35x10
-3
L
=0.057 M
C
-x
+x
+x
E
0.2-x
x
x
Convert to M
(divide by 35 x 10
-3
L)
Use moles in this chart!Slide32
3)
What is the pH when 25 mL of the base is added?
Titration of a Weak Acid with a Strong
Base
At
the equivalence point, for a strong acid with a strong base, the pH = ______. This is
not
the case for a weak acid problem. Why
?
HC
2
H
3
O
2
+ Na
+
+ OH
-
Na
+ + C2H3O2- + H2O
Ex. 25.0mL of 0.200 M HC2H
3O
2 is titrated with 0.200 M NaOH.Slide33
What
is the pH after 26 mL of
NaOH has been added?
Titration of a Weak Acid with a Strong
Base
After
the equivalence point has been reached, the additional OH
--
has nothing left to react with so the pH is determined
by ______________________________.
25mL reacts, 1mL of
NaOH
left
Ex.
25.0mL
of 0.200 M HC
2
H
3
O
2
is titrated with 0.200 M
NaOH
.Slide34
Conclusions for Titrations of Weak
Acids
The
pH of a weak acid is ___________ initially than a strong acid of the same concentration
because
The
pH rises rapidly in the early part of a titration, but more slowly near the _____________ ________
because
The
pH at
the
equivalence point
is
not _________
because Slide35
Titration of a Weak Acid with a Strong
Base
HC
2
H
3
O
2
NaOH
The titration curve for a weak acid with a strong base is similar to the curve for a strong acid with a strong base. Construct a titration curve for this problem and compare it to the curve for a strong/strong titration.