Transcript Acids, Bases, and Salts

Acids and Bases
http://www.unit5.org/chemistry/AcidBase.html
Buffers
Buffers
A buffer system is a solution that can
absorb moderate amounts of acid or
base without a significant change in pH.
They contain relatively high concentrations of
a weak acid and a salt of that acid – or a weak
base and it’s salt.
Buffers control pH because they contain an
acid that can react with added base and also
react with any added acid.
Buffers
Example: the human bloodstream, where
blood is buffered principally by the hydrogen
carbonate ion:
HCO3-1 + H3O+1 → H2CO3 + H2O
HCO3-1 + OH-1 → H2O + CO3-2
This buffer system can neutralize the 10-20
moles of carbonic acid, plus phosphoric
acid and lactic acid that the body produces
daily.
Titration
Author: J.A.Freyre
• Titration
– Analytical method Titration
(laboratory) in which a standard
solution is used to determine the concentration of an
unknown solution.
standard solution
Standard solution~
Any solution for which the
concentration is precisely
known.
unknown solution
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Titration
• Equivalence point (endpoint)
– Point at which equal amounts of
H3O+ and OH- have been added.
– Determined by…
• dramatic change in pH
• indicator color
change
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Acid-Base Titration
14.55 mL
How to read a buret volume
23
24.55 mL?
23.45 mL
(not 24.55 mL)
24
Titration
indicator -changes color
to indicate pH change
e.g. phenolpthalein is colorless in acid
and pink in basic solution
endpoint
pink
equivalence
point
pH
7
Pirate…”Walk the plank”
once in water, shark eats and
water changes to pink color
base
Acid-Base Titrations
Titration of a Strong Acid With a Strong Base
14.0
12.0
Solution
of NaOH
10.0
OHNa+
Na+
pH
-
OH- OH
Na+ Na+
OH-
8.0
equivalence point
6.0
4.0
Solution
of HCl
H+
Cl-
2.0
Cl
H+
H+
Cl-
H+
Cl-
0.0
0.0
10.0
20.0
30.0
40.0
Volume of 0.100 M NaOH added
(mL)
Additional
Adding
additional
NaOH
NaOH
from
isNaOH
added.
the buret
is added.
pH
to increases
hydrochloric
pH rises
and
as
acid
theninlevels
the flask,
off as
the
NaOH
a strong
equivalence
is acid.
addedInbeyond
point
the beginning
is the
approached.
equivalence
the pH increases
point. very slowly.
Titration Data
pH
0.00
10.00
20.00
22.00
24.00
25.00
26.00
28.00
30.00
40.00
50.00
1.00
1.37
1.95
2.19
2.70
7.00
11.30
11.75
11.96
12.36
12.52
Solution
of NaOH
Na+
OH-
OHNa+ Na+
OH-
Solution
of HCl
H+
Cl-
25 mL
14.0
12.0
10.0
8.0
equivalence point
6.0
4.0
2.0
OHNa+
Titration of a Strong Acid With a Strong Base
pH
NaOH added
(mL)
0.0
0.0
10.0
20.0
30.0
40.0
Volume of 0.100 M NaOH added
(mL)
ClH+
H+
Yellow
Blue
Cl-
H+
Cl-
Bromthymol blue is best indicator: pH change 6.0 - 7.6
Titration of a Strong Acid With a Strong Base
(20.00 mL of 0.500 M HCl by 0.500 M NaOH)
14.0
12.0
Color change
alizarin yellow R
10.0
Color change
phenolpthalein
pH
8.0
Color change
bromthymol blue
equivalence
point
6.0
Color change
bromphenol blue
4.0
Color change
methyl violet
2.0
0.0
0.0
10.0
20.0
30.0
Volume of 0.500 M NaOH added
(mL)
Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 680
Titration of a Weak Acid With a Strong Base
Titration of a Weak Acid With
a Strong Base
Titration Data
14.0
NaOH added
(mL)
12.0
10.0
pH
equivalence point
8.0
6.0
4.0
2.0
0.0
0.0
10.0
20.0
30.0
Volume of 0.100 M NaOH added
(mL)
40.0
0.00
5.00
10.00
12.50
15.00
20.00
24.00
25.00
26.00
30.00
40.00
pH
2.89
4.14
4.57
4.74
4.92
5.35
6.12
8.72
11.30
11.96
12.36
Phenolphthalein is best indicator: pH change 8.0 - 9.6
Titration of a Weak Base With a Strong Acid
Titration of a Weak Base With a Strong Acid
Titration Data
14.0
HCl added
(mL)
pH
0.00
10.00
20.00
30.00
40.00
45.00
47.00
48.00
49.00
50.00
51.00
11.24
9.91
9.47
8.93
8.61
8.30
7.92
7.70
7.47
5.85
3.34
12.0
pH
10.0
8.0
6.0
equivalence point
4.0
2.0
0.0
0.0
10.0
20.0
30.0
40.0
Volume of 0.100 M HCl added
(mL)
50.0
Titration
• Concentration of the unknown can be
determined mathematically if you know:
– The balanced neutralization reaction
– The concentration of the standard
– The volume of the standard used
– The volume of the unknown used
Titration
sunnyside
muriatic acid
30.0 mL of 2.0 M of NaOH
? M of HCl
10.5 mL
HCl must be ~ __x
6
more concentrated
than the NaOH.
If it requires 10.5 mL of ? M HCl to titrate 30.0 mL of 2.0 M NaOH to its endpoint:
what is the concentration of the HCl?
(x M)(10.5 mL) = (2.0 M)(30.0 mL)
M1V1 = M2V2
X = 5.7 M
10.5 mL of HCl
HCl(aq)  H+(aq) + Cl-(aq)
MH VH = MOH VOH
+
+
-
-
0.1 M
MH VH n = MOH VOH n
+
+
-
-
30.0 mL of NaOH with bromthymol blue indicator
Endpoint of titration is reached…color change.
Al(OH)3(aq)  Al3+(aq) + 3 OH-(aq)
0.1 M
0.1 M
H2SO4(aq)  2 H+(aq) + SO42-(aq)
0.1 M
“0.2 M”
0.1 M
proper term is Normality (N)
0.1 molar H2SO4 is 0.2 normal
Titration
+
O
moles H3 = moles
MVn = MVn
M: Molarity
V: volume
n: # of H+ ions in the acid
or OH- ions in the base
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OH
Titration
Solution
Solution
of
of KOH
NaOH
42.5 mL of 1.3M KOH are required
to neutralize 50.0 mL of H2SO4
Find the molarity of H2SO4.
2 KOH + H2SO4 → K2SO4 + 2 H2O
H3O+
OH-
M=?
M = 1.3M
V = 50.0 mL
n=2
V = 42.5 mL
n=1
Solution
of H2SO4
50.0 mL
MV# = MV#
M(50.0mL)(2)
=(1.3M)(42.5mL)(1)
M = 0.55M H2SO4
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