Chapter 7
Let the Titrations Begin
1
Terms and Concepts

What is Titration

Addition of reagent in increments until a
reaction is complete.



A base being added to an acid until the acid is
fully neutralized.
NaOH + HCl = H2O + Na+ + ClNa+ + OH- + H+ + Cl-
=
2
Titration
Titrate
trans. To ascertain the amount of a constituent
in (a mixture, or (less usually) a compound) by
volumetric analysis; i.e. by adding to a solution
thereof of known proportion, a suitable reagent
of known strength, until a point is reached at
which reaction occurs or ceases.

OED
3
Titration

Citations of the term

1870 G. E. DAVIS in Eng. Mech. 4 Mar. 605/2 In titrating iron solutions, the
ferrocyanide is not used. 1872 WATTS Dict. Chem. VI. 154 It is easy by
means of the latter to titrate sulphuric, oxalic, or any other acid with perfect
certainty. 1899 J. CAGNEY Jaksch's Clin. Diagn. i. (ed. 4) 4 Tauszk weighs
the blood used, and titrates with tropæolin or litmus

.
OED
4
Titrations

Which spring from a French word.

Titre or Titer


1. The fineness of gold or silver; in Chem. the strength of a solution as determined by titration; in
Med., the concentration of an antibody, as measured by the extent to which it can be diluted before
ceasing to give a positive reaction with antigen.
1839 URE Dict. Arts 858 The French rule for finding the par of a foreign gold coin,..is to multiply its
weight by its standard or titre. 1868 Chem. News 13 Mar. 132/1 Provided the ‘tinctorial’ power, and
consequently ‘titre’ of the ammonia standard be correctly ascertained in terms of the iodine solution,
the former may be dispensed with. 1903 Amer. Chem. Jrnl. Mar. 188 The solution was kept cooled to
15°. One cc. was removed at intervals (5 cc. in all), and the ‘immediate’ titer was found to gradually
decrease from its original value of 6·4 to 1·2 in about one-half hour, the total active oxygen
content..remaining the same. 1918 [see PEPTIDASE]. 1947 Ann. Rev. Microbiol. I. 337 If soluble
antigen has been released it may be detected in relatively high titer in the supernatant fluid. 1958
Spectator 19 Sept. 379/1 The shot I'm going to give you..ought to moderate the symptoms until
you've developed a high anti-body titer of your own. 1979 Jrnl. R. Soc. Arts CXXVII. 421/1 As the
anti-body titres waned they would go through a succession of mid-gestation abortions.
OED
5
Titration

Devices
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Titration

Wide variety of reactions can be set up to
work with titration


Acid Base
Precipitation


Complex formtion


Ag+ + Cl- = AgCl(s)
EDTA4- + Ca2+ = Ca(EDTA)2-
Redox

2 MnO4- + 5 H2C2O4 + 6 H+ = 2 Mn2+ + 10 CO2 + 8 H2O
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Titration

Equivalence Point


The point were all the reactants are used
up to make product. No excess titrant.
End Point

The point were you sense that the above
has been reached. You need a small
excess of titrant to change the color of
solution.
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Titration

Indicators

Acid Base



Phenolphthalein
Methyl Red
Many, many more.
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Structure of Phenolphthalein
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Titration

This difference in the equivalence point
and the end point is call the 
Titration error and can be determined by
doing a blank titration.
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Titrations


Since you are comparing moles of
titrant to moles of analyte then you
must know the moles of titrant very
accurately.
This is where standards come in.
15
Titration


A standard is a solution, solid or some
material that we know its concentration
or purity very accurately.
We can pay someone to provide this for
us. For example, in the vinegar lab we
used the “cube”. This was made up by
Fisher and they gave us the value.
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Titration



This might not work depending what
your lab regulatory environment is.
You might need to check to see if Fisher
has given you the proper concentration.
They make errors!!!

This would be a raw materials quality
control issue.
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Titration



We will need often to go back to a
primary standard.
For Acid Base titrations this is KHP
KHP is not Potassium Hydrogen
Phosphorus.
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Titration

KHP

Potassium Hydrogen Phthalate


Or Potassium Biphthalate or other possible
names.
It is the mono-potassium salt of phthalic
acid
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Titration
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Titration

What are characteristics of a primary
standard.




99.9 pure or better (but known exactly)
Not decompose on standing
Not decompose on drying
High equivalent weight
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Titration

Once you have prepared your solution
you now have your standard. This
concentration will be used in your
determination.
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Titration

Vinegar Lab


We made up a solution of NaOH. NaOH is
not available as a primary standard since
the material is sold as solid hemispherical
pellets that absorb water and CO2
So we prepare an approximate
concentration and standardize this solution
with the acid from the “cube”.
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Titration



We depend on the supplier to give us
the proper assay. For us it has been
0.0998M, 0.1000M and 0.1003M
We are fairly safe with this since it is
hard to introduce contamination to the
“cube”.
What was the expiration date???
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Titration


Issues such as expiration date and
supplied concentration are issues in
GLP.
We then determined the assay of the
NaOH and used this value to determine
the percent acid in the vinegar.
25
Titration



We did a direct titration. Added base
until the endpoint was reached.
We also could have done a back
titration. This is where you add excess
titrant and titrate the excess and
determine the number of moles of
titrant used by the initial analyte.
This is the basis of a Kjeldahl titration
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Titration

The Kjeldahl is used to determine %
nitrogen (protein content). Important
in the feed industry.




Protein digested to NH3
NH3 then bubbled into excess HCl (aq)
The amount of excess HCl is determined by
titration with NaOH.
Amt (NH3) = Amt HCl (start) – Amt HCl (left
over)
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Titration



We can, and often do, carry out titration
without indicators. We can follow a
titration with an instrumental response.
Spectrophotometer. (Spec 20)
Potentiometric Titration (pH or other
electrode)
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Titration


Spectrometric Example.
HST titrated with Ferric nitrilotriacetate
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Titration

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
Precipitation Titration
It is common to titrate halides with
silver to form the precipitate.
Monitor this titration with a silver
electrode.
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34
Titration

Electrode will respond to the potential
of the silver ion in solution. pAg

pAg = -log[Ag+]

pCl = -log[Cl-]
35
Titration


We monitor the pAg as we add silver
ion. We will see the classical titration
presentation.
We can calculate this curve based on
our understanding of chemistry.
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37
Titration

We can calculate the amount of silver
ion from three separate regions of the
curve.



Before EP (Silver limited by common ion)
At EP (Only Silver in solution due to Ksp)
After EP (Silver just added to water)
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Titration

Since Ksp of the three halides are
significant different then we can use
this procedure to determine mixtures of
halide ions in solution.
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40
Titration


We can also use indicators for silver titrations.
Also referred to as Argentometric titrations.
Endpoint methods.


Volhard – soluble colored complex at end point
Fajans – adsorption of colored indicator on the
precipitate at the end point
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Titration

Volhard





Ag+ + Cl- = AgCl(s)
Remove precipitate
Back titrate excess silver with thiocyanate
Ag+ + SCN- = AgSCN(s)
Fe3+ + SCN- = FeSCN2+ (red)
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Titration

Fajans

Adsorption indicator is used and when the
end point is reached the indicator attaches
to the precipitate and changes color.
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Titration
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Titration

Do the problem on my home page.

It will be an excellent review of Ksp
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