Chapter 4
Titration and oxidation numbers
Part VI
Titration
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Acid base reactions are
often called
neutralization reactions.
One type of
neutralization reaction is
a titration.
Titration: using a
measured volume of a
solution of known
concentration to find the
concentration of an
unknown solution.
Vocabulary
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Titration is a type of volumetric analysis.
Titrant: aka standard solution.
Analyte: solution being analyzed.
Equivalence point: where [H+] = [OH-]
The equivalence point is marked with a
color change by an indicator. (as close as
possible)
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This color changed is called the endpoint.
Requirements
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1.
2.
3.
There are 3 requirements for a
successful titration.
The exact reaction between titrant and
analyte must be known (and rapid).
The equivalence point must be
accurately marked.
The volume of the titrant used to reach
equivalence point must be known
accurately.
Titration
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Not all titrations are
acid-base
neutralization
reactions.
The next lab is a
neutralization titration
known as
Standardization of a
Solution.
Example: Standardization
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A 1.3009 g sample of KHP potassium
hydrogen phtalate (KHC8H4O4) with molar
mass of 204.22 g/mol is weighed out. It has
one acidic hydrogen.
It is dissolved in water and phenolpthalein,
an indicator is added.
The student titrates the unknown NaOH to
the pink endpoint. The difference in the
buret reading is 41.20 mL.
Calculate the concentration of NaOH.
Answer:
Reaction:
OH- (aq)+ HC8H4O4- (aq) H2O (l)+ C8H4O42(aq)
Ratio is 1:1
1.3009g KHP x 1mol/204.22g=0.0063701 mol
KHP
0.0063701 mol KHP = 0.006371 mol NaOH
M NaOH = 0.0063701 mol NaOH/0.04120 liters
0.1546 M NaOH
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A tough one:
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You have a mixture of carbon
tetrachloride, (CCl4) and benzoic acid
(HC7H5O2) a weak acid with one acidic
hydrogen. A sample of this mixture
weighing 0.3518 g was mixed with water
and the resulting solution required 10.59
mL of 0.1546 M NaOH for neutralization.
What was the mass percent of benzoic
acid in this solution?
Answer:
You have both CCl4 and HC7H5O2 in solution
but only the acid will react with NaOH, and in
a 1:1 ratio.
HC7H5O2(aq) + OH-(aq)  H2O(l) +C7H5O2- (aq)
 How many moles of NaOH used?
10.59ml x (1L/1000mL) x (0.1546 mol/1 L)=
0.001637 mol OH- = 0.001637 mol HC7H5O20.001637 mol HC7H5O2 x 122.12g/1 mol
= 0.1999 g HC7H5O2
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Is that the answer?
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% mass
(0.1999 g of acid/ 0.3518 total mass)*100
=56.82%
Reread the question!!
Oxidation Rules
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In many reactions there
is an exchange of
electrons.
This transfer is called an
oxidation-reduction
reaction of redox for
short.
LEO says GRE
Oxidation states or Oxidation
numbers
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1.
2.
3.
A method for tracking electrons:
6 simple rules
An atom in an element is zero Na(s)
O2(g)
A monatonic ion is the same as its
charge. H+ =+1, O2- = -2
Fluorine is -1 in its compounds
Oxidation states or Oxidation
numbers cont.
Oxygen is usually -2 in its compounds.
The exceptions are peroxides O2-2 O=-1
5. Hydrogen is +1 in its compounds
4.
6.
Also Important: the sum of oxidation
numbers in a neutral compound = zero.
The sum of oxidation numbers in an ion
equal its charge.
Try
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CO2
SF6
NO3C=+4, O=-2
S=+6, F=-1
N=+5 , O=-2