LECTURE 2
Titration method
ass. prof. I. R. Bekus
Titrimetric analysis- is a method of quantitative analysis
used to determine unknown concentration of known
substance.
 You
must know definition of some useful
terms:
 Titrant or Standard solution – a solution of
accurately known concentration.
 Titration – the process of determining
unknown concentration by adding the small
increments of standard solution until the
reaction is just complete.
Overview of Titrimetry:
Titrimetric methods are classified into four groups
based on the type of reaction involved.
These groups are acid–base titrations, in which an
acidic or basic titrant reacts with an analyte that is a
base or an acid; complexometric titrations involving a
metal–ligand complexation reaction; redox titrations,
where the titrant is an oxidizing or reducing agent;
and precipitation titrations, in which the analyte and
titrant react to form a precipitate..
Equipment for Measuring
Volume
Analytical chemists use a variety of glassware to
measure volume: beaker; graduated cylinder;
volumetric flask; pipette; dropping pipette.
(a)
(b)
(c)
(d)
Common types of pipettes and syringes: (a) transfer
pipette; (b) measuring pipette;
(c) digital pipette; (d)
syringe.
Burette – kind of laboratory glass for exact
measurement of volume of solution used. Burette is
graduated and has a burette tap or stopcock at one
extreme end to control the flow of titrant.
Equivalence point. The point in a titration at which the
amount of titrant added is chemically equivalent to
the amount of substance titration.
End point. The point at which the completion of a
reaction is practically observed. When using an
indicator, the end point occurs when enough titrant
has been added to change the color of the indicator.
Three important precautions are needed when
working with pipettes and volumetric flasks.
First, the volume delivered by a pipette or contained
by a volumetric flask assumes that the glassware is
clean.
 Second, when filling a pipette or volumetric flask, set
the liquid’s level exactly at the calibration mark.
 Sird, the liquid’s top surface is curved into a
meniscus, the bottom of which should be exactly
even with the glassware’s calibration mark.

Burette filling instruction
 Always
use a small funnel to fill a burette
 To fill a burette, close the stopcock at the bottom.
You may need to lift up the funnel slightly, to
allow the solution to flow in freely
 Fill the burette past the zero mark
 Check the tip of the burette for an air bubble. To
remove an air bubble you must lift up tip of
burette and then open stopcock. If an air bubble is
present during a titration, volume reading may be
in error!
 Take the funnel out of the burette so that drops of
solution from the funnel will not fall into the
burette.
When you burette is filled, with no air bubbles, you
must level of the liquid to exactly the zero mark. Read
the bottom of the meniscus. Be sure your eye is at the
level of meniscus, not above or below
After filling burette, a known volume of the unknown
concentration solution should be taken with the pipette
and placed into the conical flask, along with a small
amount of the indicator.
Slowly release known solution from the burette into
the conical flask, while swirling the mixture.
The solution should be let out of the burette until the
indicator changes colour and value on the burette should
be recorded.
Types of Titration
Neutralisation
(Acid-Base) titration
Precipitation titration
Reduction-Oxidation (Redox)
titration
Complexometric titration
Acid-Base Titration
As the second step in this investigation you are now going to
compare two solutions (an acid and a base) using a method
called "titration".
In the first procedure you are simply going to add an acid
solution to a basic solution. Each solution will be of a different
"strength", or concentration, or amount, and you will simply
observe the relative results.
In the second procedure you are going carry out a number of
titrations in which an acid solution is carefully added to a basic
solution. In each case you have to find the "end point", which
is the point at which you have added just enough of the acid
solution to exactly neutralize all the base that was in the
original solution.
The properties of the acid solution are standardized, and fully
known. So, by finding the exact amount of acid that
neutralizes a known solution of base, it is possible to carry out
a calculation and find out the molecular weight of the base.



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These titrations are based on the neutralization reaction
that occurs between an acid and a base, when mixed
in solution.
A neutralization reaction in aqueous solution is a
reaction of an acid and a hydroxide base to
produce a salt and water
An acid-base titration is the determination of
the concentration of an acid or base by
exactly neutralizing the acid/base with an acid
or base of known concentration. This allows
for quantitative analysis of the concentration
of a unknown acid or base solution.
An acid-base titration in which a base is
titrated with a standard solution of an acid is
called Acidimetric
An acid-base titration in which an acid is
titrated with a standard solution of an alkali
(a base) is called Alkalimetric
Precipitation Titration
Precipitation Titration it is a volumetric titration method where the reaction between
the titrant and sample solution yield precipitate (low solubility, usually ionic
compounds)
The most important precipitating reagent is silver nitrate.
Titrimetric methods based upon silver nitrate are sometimes termed argentometric
methods.
Argentometry, where the titrant is a standard AgNO3 solution is the most common
precipitation titrimetric method, because
 silver precipitates are usually highly insoluble
 many species form steichiometric precipitates with Ag+ (e.g. Cl-, Br-, I-, F-, CN-,
SCN-, CrO42-, PO43- etc.)
 these precipitates are formed quickly
Titrant is a standardized AgNO3 solution. The titrant needs to be stored in a dark
(brown) container.
Argentometry is most often used for determination of chloride ions, but it can be used
for other halides (bromide, iodine).
There are 3 techniques of end point determination:
 method of Mohr (indicator: potassium chromate)
 method of Volgard (indicator: ferric salt)
 method of Fajans (indicator: fluorescein)
The most often used Mohr method
Mohr method
Mohr titration is used for determination
of halide in a solution.
Potassium chromate can serve as an
indicator for the determination of
chloride, and bromide ions by
reacting with silver ion to form a
brick-red silver chromate (Ag2CrO4)
precipitate in the equivalence-point
region.
Mohr titration has to be performed at a neutral or weak
basic solution of pH 7-9 (or 6-10), because silver
hydroxide forms at high pH, while the chromate forms
H2CrO4 at low pH, reducing the concentration of
chromate ions and delaying the formation of the
precipitate.
If Ag+ solution is add to a Cl- solution containing of small
quantity of CrO4-, then AgCl will firstly precipitated,
while Ag2CrO4 has not yet, and concentration Ag+
increases progressively until solubility product of the ions
reach the value of Ksp Ag2CrO4 (2,0·10-12) to form
brick-red precipitate.
Before titration small amount of sodium or potassium
chromate is added to the solution, making it’s slightly
yellow colour. During titration, as long as chlorides are
present, concentration of Ag+ is too low for silver
chromate formation. Near equivalence point concentration
of silver cations rapidly grows, allowing precipitation of
brick-red silver chromate which signals end point.
Reduction-Oxidation (Redox) Titration
A redox titration is based on an oxidation-reduction reaction between
analyte and titrant.
In this experiment you will use a standard solution of potassium
permanganate (KMnO4) to determine the of iron (as Fe2+) in an
unknown solution.
Permanganate ion reduces to a manganese (II) ion in the acidic
solution. This reaction requires 5 electrons and 8 hydrogen ions:
MnO4-+ 8H+ + 5 e- = Mn2+ + 4H2O
Only one electron is necessary to reduce Fe (III) to Fe (II)
Fe3+ + e- = Fe2+
Therefore, 1 mole of MnO4-(the oxidizing agent) reacts with 5 moles
of Fe2+ (the reducing agent) to form 5 moles of Fe3+ and 1 mole of
Mn2+. Thus, in net ionic form:
MnO4- + 5Fe2+ + 8H+ = 5Fe3+ + Mn2+ + 4H2O
Reactions in which electrons are transferred from one
species to another are known as redox reactions,
or oxidation-reduction reactions.
2 Na + Cl2  2 NaCl
A redox reaction is made up of two reactions:
reduction -- gain of electron(s)
oxidation -- loss of electron(s)
Writing Redox Equations
In a redox reaction, the number of electrons
lost by the species being oxidized must
balance the number of electrons gained by
the species being reduced.
In a balanced redox reaction equation:
* the number of atoms of each element
must be balanced
* the total charge on the ions on the left
hand side of the equation will equal the
total charge on the ions on the right hand
side of the equation
In the redox titrations, we need a
chemical species that can change
colour in the potential range
corresponding to the sharp change at
the end point. A chemical substance,
which changes colour when the
potential of the solution reaches a
definite value, is termed as an
oxidation-reduction or redox indicator.
Inox +
ne → Inred
colour A
colour B
Permanganatometry
Potassium permanganate is a very strong oxidizing agent and
is employed in the estimation of reducing agents like ferrous
salts, oxalic acid, arsenious oxide, etc.
The permanganate ion, MnO4-, gets reduced to Mn2+ ion in
acidic medium and to MnO2 in neutral and alkaline media.
Titrations involving potassium permanganate are usually
carried out in acidic medium.
Since MnO4– is intense purple while Mn2+ is colour less, the
reaction mixture at equivalence point is colour less and even a
single drop of the permanganate would impart sufficient pink
colour to the solution acting as self indicator.
The reducing agent in the titration to be discussed is oxalic
acid here. The composition of it is H2C2O4·2H2O. In spite of
being a dehydrate it is a good primary standard as its
composition is unchanged during storage or weighing.
This redox reaction can be split apart in two parts- one
showing the oxidation and the other reduction
This titration is carried out in warm conditions
(temperature about 60 C). The reaction at room
temperature is slow because of the equilibrium
nature of this reaction. CO2 is highly soluble in
water and thus heating removes all dissolved carbon
dioxide out of the solution.
While noting the burette readings, it should be taken
into account that the solution is so intensely
coloured that the lower meniscus of the solution
may not be clear. Thus for permanganate titrations
the upper meniscus in the burette is noted.
Complexometric titration
Erio - T indicator or Eriochrome
Black-T indicator is used in this
titration.
EDTA is a versatile chelating agent.
A chelating agent is a substance
whose molecules can form several
bonds to a single metal ion.
Chelating agents are multi-dentate
ligands. A ligand is a substance
that binds with a metal ion to form
a complex ion. Multidentate
ligands are many clawed, holding
onto the metal ion to form a very
stable complex. EDTA can form
four or six bonds with a metal ion.
The picture on the left shows the color of the indicator
before titration.
This color change from wine red to violet to
blue is due to the compact nature of the
complex. The statement "the compact nature
of the complex" means when the indicator is
added to the hard water, the indicator Erio-T
forms a complex with the Ca+2 ions that is
pink in color. As EDTA is added to the
solution, the EDTA forms a complex with the
Ca+2 leaving the indicator Erio-T
uncomplexed, which is blue in color.
pH scale
ACID
NEUTRAL
BASE (ALKALINE)
0-----------------------------7--------------------------------14
Acid - Base indicators
Acid - Base indicators (also known as pH indicators) are
substances which change colour with pH. They are
usually weak acids or bases, which when dissolved in
water dissociate slightly and form ions.
The acid and its conjugate base have different colours.
At low pH values the concentration of H3O+ is high
and so the equilibrium position lies to the left. The
equilibrium solution has the colour A. At high pH
values, the concentration of H3O+ is low - the
equilibrium position thus lies to the right and the
equilibrium solution has colour B.
Most commonly used indicators in acid-base titration are:
N1V1=N2V2
From the total volume of known solution needed to react the end point, the
concentration of the unknown solution can be calculated.
 N1 – normality of solution with known concentration
 V1 – volume of solution with known concentration
 N2 – normality of solution with unknown concentration
V2 – volume of solution with unknown concentration
Example:
Problem.
30 ml of 0.10N NaOH neutralised 25.0 ml of hydrochloric acid. Determine the
concentration of the acid.
Solution.
N1- normality of NaOH = 0,1 mol-equiv/l
V1 - volume of NaOH = 30 ml
V2 - volume of HCl = 25 ml
N2 - normality of HCl - ?

N1  V1 0,1  30
N2 

 0,12 mol  equiv / l
V2
25
Thank you for attention