Modern Chemistry
Chapter 15
Acid-Base Titration
and pH
Sections 1 & 2
Aqueous Solutions and the Concept of pH
Determining pH and Titrations
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
1
Determining pH
and
Titration
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
2
Chapter 15 Vocabulary
•
•
•
•
•
•
•
•
Self Ionization
pH
pOH
Acid-base indicator
Transition interval
Titration
Equivalence Point
Endpoint
• Standard Solution
• Primary Standard
• Standardization
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
3
p. 511
Indicators
• Acid-base indicators- compounds whose
colors are sensitive to pH
HIn

Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
H+ + In-
4
Indicators
• Transition Interval – the pH range over
which an indicator changes color
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
5
p. 513
Color Range of Indicators
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
6
p. 513
Color Range of Indicators
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
7
p. 513
Color Range of Indicators
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
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p. 512
pH of Common Materials
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
9
pH Meter
• Determines the pH of a solution by
measuring the voltage between two
electrodes that are placed in a solution
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
10
How does a pH meter work?
In 1901 a German chemist named Fritz Haber
discovered that the voltage at certain glass surfaces
changed in a regular manner with the acidity of a
solution. Modern pH sensing electrodes are a
refinement of this fundamental discovery.
The pH electrode consists of a thin
membrane of Hydrogen sensitive glass blown on
the end of an inert glass tube. Because this is a
special type of glass and very thin, the bulb is very
fragile and great care must be exercised in handling
it.
This tube is filled with an electrolyte, and the
signal is carried through Ag/AgCL wire. This is a pH
half cell.
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
11
Titration
• 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.
• A quantitative lab procedure to determine
concentration or amount.
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
12
Doing a Titration
p. 518
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
13
Doing a Titration
p. 518
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
14
Doing a Titration
p. 518
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
15
Doing a Titration
p. 519
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
16
Doing a Titration
p. 519
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
17
Doing a Titration
p. 519
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
18
Titration Video
Glencoe Disc 3
Insert Holt Disc 2
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
19
Titration
• Equivalence point – the point at which the
two solutions in a titration are chemically
equivalent.
M
=
mol/L
• MOLESbase = MOLESacid
mol = MxL
• If the coefficients are all 1 then the mole
ratio has no effect so…
• MB x LB = MA x LA
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
20
Titration
STANDARD
SOLUTION
ANALYTE
IN BURETTE
IN FLASK
25 mL of base
0.2M known
concentration
of base
10 mL of acid
X M unknown
concentration
of acid
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
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Equivalence Points
Titration Combination
Equivalence
Point
STRONG acid + STRONG base
pH=7
STRONG acid +
WEAK
base
pH<7
acid + STRONG base
pH>7
WEAK
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
22
Equivalence Point & Endpoint
• Endpoint – the point in a titration at which
an indicator changes color.
If the
equivalence
point is 7,
what is the
best indicator
to use?
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
23
Titration Curve
p. 517
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
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Titration Curve
p. 517
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
25
Standardization
• Standard solution – a solution that contains
the precisely known concentration of a
solute.
• The standard solution has be
“standardized” (determined its
concentration) with a “primary standard” (a
solution with a known concentration).
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
26
Molarity & Titration
M = mol/L
mol = MxL
• MOLESbase = MOLESacid
1. Calculate the moles of the substance in
which you know the molarity and
concentration.
2. Use the mole ratio to convert these moles
to moles of the other substance.
3. Now that you have moles of the other
substance divide by liters of that
substance to get molarity.
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
27
Sample Problems p.520
In a titration, 27.4 mL of 0.0154 M Ba(OH)2 is
added to a 20.0 mL sample of HCl solution
of unknown concentration until the
equivalence point is reached. What is the
molarity of the acid solution?
4.22 × 102 M HCl
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
28
Molarity & Titration
1. Calculate the moles of the substance in
which you know the molarity and
concentration.
0.0154 M Ba(OH)2 x 0.0274 L Ba(OH)2 =
0.000422 moles Ba(OH)2
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
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Molarity & Titration
2. Use the mole ratio to convert these moles
to moles of the other substance
Ba(OH)2 (aq) + 2HCl
(aq)
 BaCl2 (aq) + 2HOH
x
(l)
2 mole HCl
1 moles Ba(OH)2
= 0.000844 moles HCl
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
MOLE RATIO
(coefficients)
30
Molarity & Titration
3.Now that you have moles of the other
substance divide by liters of that substance
to get molarity.
0.000844 moles HCl
= 0.0422 M HCl
0.0200 L HCl
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
31
Practice Problems p.521
• 1. A 15.5 mL sample of 0.215 M KOH
solution required 21.2 mL of aqueous acetic
acid solution in a titration experiment.
Calculate the molarity of the acetic acid
1. 0.157 M CH3COOH
solution.
• 2. By titration, 17.6 mL of aqueous H2SO4
neutralized 27.4 mL of 0.0165 M LiOH
solution. What was the molarity of the
aqueous acid solution? 2. 0.0128 M H2SO4
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
32
Ch 15 Sec 2 Homework
Titration Calculations Worksheet
Chapter 15 Sec 2 Determining pH
& Titration p. 511-521
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