Titrations
Acid-base indicators are…
• Compounds whose color is sensitive to
pH.
• Either weak acids or weak bases.
• pH paper is a universal indicator. It is
made by soaking the paper in several
different indicators.
Phenolphthalein
• An indicator that changes color from clear
in acid to pink in base (pH 8-10).
• This is the indicator that we will use in the
lab during titrations.
Titrations
• The controlled addition and measurement
of the amount of a solution of known
concentration (NaOH) required to react
completely with a measured amount of a
solution of unknown concentration (HCl).
• Neutralization: A + B  Salt + H2O
• The point of neutralization is the endpoint
= change in color of indicator
Good color!
Too much base!
Drill #10
5/7, 5/8/14
• Fill in the following table. Need to use your
scientific calculator.
Solutions
1.0×10-3M
HClO4
0.010 M HCl
[H+]
pH
[OH-]
1.0×10-3M
3.0
1.0×10-11M
11
1.0×10-2M
2.0
1.0×10-12M
12
8
1×10-6M
6
10.8
pOH
0.000001 M
KOH
1×10-8M
6.00×10-4 HBr
6.00×10-4M
3.22
1.67×10-11M
0.20 M NaOH
5.0×10-14M
13
2.0×10-1M
.70
0.00600 H2SO4
6.00×10-3M
2.22
1.67×10-12M
11.8
Solutions
1.0×10-3M
HClO4
0.010 M HCl
0.000001 M
KOH
6.00×10-4
HBr
0.20 M NaOH
0.00600 H2SO4
[H+]
pH
[OH-]
1.0×10-3M
3.0
1.0×10-11M
11
1.0×10-2M
2.0
1.0×10-12M
12
8
1×10-6M
6
6.00×10-4M
3.22
1.67×10-11M
10.8
5.0×10-14M
13
2.0×10-1M
.70
6.00×10-3M
2.22
1.67×10-12M
11.8
1×10-8M
pOH
Agenda
•
•
•
•
Go over Titration Curve Graph
Acid and Base strength
Titration Calculation Problems
Titration Lab
Homework
• Titration Problems
• Titration Lab
Titration Curve for strong acid & strong base
Equivalence Point
• The point at which the two solutions used in a
titration are present in equal amounts
• Amount of acid in moles = Amount of base in
moles
• This can be found using an indicator – in a perfect
world, the endpoint (point at which the indicator
changes color) would be the same.
*Note: this is not the same volume or the same
concentration, just the same MOLES
Equivalence Point
• Strong acid + strong base = equivalence
point at pH of 7
• Strong acid + weak base = equivalence
point at pH of <7
• Weak acid + strong base = equivalence
point at pH of >7
How to solve titration problems:
1. Write the balanced neutralization equation
2. Solve for moles of given (using molarity and
volume)
3. Convert from moles of given to moles of
unknown using mole ratio
4. Use moles of unknown to solve for molarity
or volume.
NOTE: If moles are equivalent (coefficients)
then:
MAVA =MBVB
Assignment
• Titration Problems
Titration Lab
•
•
•
•
Place 5 ml of HCl in Erlenmeyer flask
Add 2 drops of phenolphthalein indicator to the flask
Take an initial volume buret reading
Place sheet of white paper under flask during
titration
• Titrate with .50 M NaOH until you get a pale pink
color that stays pink for about 10 secs
• Make sure you carefully swirl flask after each titration
• If you think you have reached the endpoint, record
final volume of NaOH.
Sample Titration Prob
• Record calculations on half sheet of paper.
Drill #18
5/24 & 28/13
• A student titrates a 20 ml sample of a solution of HBr
with unknown molarity. The titration requires 20.05 ml of
a 0.1819 M solution of NaOH. What is the molarity of the
HBr solution?
• Answer: 0.1824 M
• A 35 ml sample of ammonium hydroxide is titrated to the
end point with 54.95 ml of a 0.400 M sulfuric acid. What
is the molarity of the ammonium hydroxide?
• Answer: 1.26 M
Agenda
• Go over Review Packet
• Test
Drill #16
5/22 & 23/13
Calculate the pH for the following solutions and
indicate whether the solution is acidic (A), basic (B),
or neutral (N).
1.
2.
3.
4.
[H+] = 1 x 10-2 M
[OH-] = 1 x 10-2 M
[OH-] = 1 x 10-8 M
[H+] = 1 x 10-6 M
What are the [OH-] for solutions with the following
ph values?
5. 4.0
6. 8.0
Drill #16
5/22 & 23/13
Calculate the pH for the following solutions and
indicate whether the solution is acidic (A), basic (B),
or neutral (N).
1.
2.
3.
4.
[H+] = 1 x 10-2 M – 2, A
[OH-] = 1 x 10-2 M – 12, B
[OH-] = 1 x 10-8 M – 6, A
[H+] = 1 x 10-6 M – 6, A
What are the [OH-] for solutions with the following
ph values?
5. pH = 4.0; pOH = 10; [OH-] = 1 x 10-10 M
6. pH = 8.0; pOH = 6; [OH-] = 1 x 10-6 M
Drill #17
5/22 & 23/13
Write the names for the following acids and bases:
KOH
b) HF
c) H2SO3
d) Fe(OH)2
e) HCN
a)
Write the formulas for the following acids:
a) phosphorous acid
b) hydrobromic acid
c) carbonic acid
Drill #17
5/22 & 23/13
Write the names for the following acids and bases:
KOH - potassium hydroxide
b) HF - hydrofluoric acid
c) H2SO3 - sulfurous acid
d) Fe(OH)2 – iron (II) hydroxide
e) HCN - hydrocyanic acid or cyanic acid
a)
Write the formulas for the following acids:
a) phosphorous acid - H3PO3
b) hydrobromic acid - HBr
c) carbonic acid - H2CO3
Agenda
• Titration Calculations
• Titration Lab (4B – postponed until next wk)
Announcements
• Turn in Naming Bases and Crossword
Puzzle
• Test next class.
• If we know the molarity and the volume of
acid used, then can we calculate the
amount of moles of acid? How?
• MolA = MAVA
• Worksheet!
• Green workbook, pg. 272 -275
Test Topics
•
•
•
•
•
Properties of acids, bases, and salts
Bronsted-Lowry definition of acids/bases
Amphoteric substance
Neutralization reaction – must be balanced
Purpose of calculating an Acid or Base
dissociation constant
• Naming acids
• Equations for pH, pOH, [H+], and [OH-]
• Titration calculations
Objective
• SWBAT calculate molarity of acid using
data from titration.