Volumetric analysis

VOLUMETRIC ANALY
By- Shalini N. Barad
Lecturer,
Appasaheb Birnale College of Pharmacy.

• Chemical analysis plays an important role in study
of composition or constituents of substances or
material.
• The chemical analysis is broadly divided into two
types
A. Qualitative analysis
B. Quantitative analysis ---
1. Instrumental
– Colorimeter
– Spectrophotometer
2. Non-Instrumental
– Volumetric analysis
– Gravimetric analysis

• Important terminology:
1) Titration: It is a process where a solution of known
strength is added to a certain volume of treated
sample containing an indicator.
2) Titrant: A solution of known strength of conc. used in
the titration (present in burette)
3) Titrand : The titrand is any solution to which the
titrant is added & which contain the ions/ species
being determined (present in conical flask).
4) Titration curve: A plot of pH vs. ml of titrant showing
the manner in which pH changes vs. ml of titrant
during an acid-base titration.
5) Indicator: A substance / chemical that changes its
colour in acidic & basic medium during titration.

6. Equivalent point: The point at which just adequate reagent is
added to react completely with a substance.
OR
The point at which the acid has completely reacted with or been
neutralized by the base.
7. Buffer solution: A solution that resists changes in pH even when a
strong acid /base is added/ when it is dilute with water.
8. Molarity definition:
Molarity is defined as the moles of a solute per liters of a solution.
Molarity equation
M = moles solute / liters solution
9. Molality definition
It is defined as the moles of a solute per kilograms of a solvent.
Molality equation:
m = moles solute / kilograms solvent
10. Normality is described as the number of gram or mole
equivalents of solute present in one litre of a solution.

A. Volumetric analysis
• Volumetric analysis is also known as titrimetric analysis.
• The volumetric method involves measurement of volumes of the
reacting substances.
• The weight of the required constituents is indirectly obtained by
measuring the volume of a solution of known composition
required to react with a known volume of a solution containing
an unknown weight of the desired constituent.
• This is done by a process known as titration which is divided into
four types depending upon the nature of the chemical reaction.
• The four types are
a. Acid – base or neutralization methods
b. Precipitation methods
c. Complexometric methods
d. Oxidation – reduction method

o The key to performing a successful titrimetric analysis is to
recognize the equivalence point of the titration (the point at
which the quantities of the two reacting species are
equivalent), typically observed as a colour change.
o If no spontaneous colour change occurs during the titration, a
small amount of a chemical indicator is added to the analyte
prior to the titration.
o Chemical indicators are available that change colour at or near
the equivalence point of acid-base, oxidation-reduction,
complexation, and precipitation titrations.
o The volume of added titrant corresponding to the indicator
colour change is the end point of the titration.
o The end point is used as an approximation of the equivalence
point and is employed, with the known concentration of the
titrant, to calculate the amount or concentration of the analyte.
o In volumetric analysis, concentration of substances are found
out by volume determination.
o The unit used for measurement of volume of a liquid or
solution is “litre”.

Procedure for Volumetric Analysis
• A typical titration starts with a beaker or flask containing a
precise volume of the analyte and small amount of
indicator placed & burette containing the titrant.
• The solution that needs to be analyzed needs to have an
accurate weighed.
• Choosing the right kind of material to be analyzed is also
very important. A substance that reacts rapidly and
completely to produce a complete solution is chosen.
• Small quantities of titrant are added to the analyte and
indicator till the indicator changes colour in reaction to the
titrant saturation threshold reflects the arrival at the
endpoint of the titration.
• The titration has to be continued up until the reaction is
complete and the amount of reactant added is exactly the
amount that is needed to complete the reaction.

• Another important step is measuring the right
volume of the standard solution since molarity is
a standard metric to calculate the number of
moles present in a solution.
• Based on the desired endpoint, single drops or
less than a drop of the titrant makes a difference
between a permanent and temporary change in
the indicator.
• If the reagent or reactant that we use is to be
made into a standard solution then we can
weigh and dissolve the reagent into a solution,
so that it is in a definitive volume within a
volumetric flask.

The basic principle of Volumetric
analysis:
• The solution which we want to analyze contains a
chemical of unknown amount then the reagent reacts
with that chemical of unknown amount in the
presence of an indicator to show the end-point.
• End-point shows that the reaction is complete.
• Then we measure the volumes by the method of
titration which completes the reaction between the
reagent and solution, then the amount of unknown
chemical in the solution is calculated by using the
mole fraction of the equation.
• After the end-point of reaction is reached, volumetric
analysis calculations of the analyte are done by the
formula –

 Ca = Ct Vt M/Va
Where, Ca is the concentration of the analyte.
Ct is the concentration of titrant.
V is the volume of the titrant.
M is the mole ratio of the analyte and the
reactant.
V is the volume of the analyte.
 N1V1=N2V2
 is the normality equation which can be simply
derived by using the Law of equivalence, which
states that the number of gram equivalents of
reactant is equal to gram equivalents of product.

o Let’s take the example of an acid-base titration reaction to
derive this equation.
As we know,
Normality=no. of gram equivalent Volume(inL)
o Let the Normality and Volume of the Acid
be N1 and V1 and Normality and Volume of Base
be N2 and V2 .
o The no of gram equivalent will be ;
No. of gram equivalent = Normality(N) ×
Volume(V)
o And as we know,
No. of gram equivalent of Acid = No. of gram
equivalent of Base
o Hence after putting the variables, the equation will be
N1V1 = N2V2
This is our desired equation.

Types of reactions used in volumetric
analysis :
1. Acid-Base Titrations :
HA + B ↔ HB+ + A
2. Oxidation-Reduction Titrations :
AOx + BRed ↔ ARed + BOX
3. Precipitation Titrations :
M(aq) + nL (aq) ↔ MLn (s)
4. Complex Formation Titrations :
M (aq) + nL ↔ MLn (aq)

1. Acid-Base Titrations :
• Titration is the process of adding a measured volume
of an acid or base of known molarity (the standard
solution) to an acid or base of unknown molarity until
neutralization occurs.
• Importance:
1. It is used to find conc. Of an acid / base
2. Whether unknown acid / Base is stronger / weak
3. pKa of an unknown acid / pKb of an unknown
Base
• Let us consider acid-base titration which is take
place with acceptor.
• In water, proton is generally solvated as H3O+.
• Water is added to base to lose (OH-) or gain H3O +.

 Acid base reaction are reversible. The reaction are shown
below:
 HA + H2O -- H3O+ + A- (Acid)
 B- + H2O -- BH + OH- (Base)
 Here, [A] is conjugate base of H+, B is is conjugate acid
 Thus we say that,
Acid + Base -- conjugate base + conjugate acid

 Equivalence point: point in titration at which the amount of
titrant added is just enough to completely neutralize the
analyte solution.

• Indicator: A substance / chemical that changes its
colour in acidic & basic medium during titration.
• Classification of Indicator:
1. The phthalein’s & sulphothaleins indicator–
eg= Phenolphthalein
2. Azo indicator dye– Eg= Methyl orange
3. Triphenylmethane Indicator– Eg= Malachite green.
• Choice of indicator based on Types of titrations-
1. Strong acid- strong base= Phenolphthalein
2. Weak acid- strong base= Phenolphthalein show color
change at Equivalence point.
3. Strong acid- Weak base = Methyl orange
4. Weak acid- Weak base = No indicator suitable

2. Non-aqueous titration
• Non-aqueous titration refers to a type of titration in
which the analyte substance is dissolved in a
solvent which does not contain water (non
aqueous solvent/ organic solvent).
• Ex: chloroform, benzene, ammonia, pyridine,
acetic acid, alcohols, CCl4 etc.
• it is suitable for the titration of very weak
acids and very weak bases, and it provides a
solvent in which organic compounds are soluble.

• Theory
• The need for non-aqueous titration arises because
water can behave as a weak base and a weak acid as
well, and can hence compete in proton acceptance or
proton donation with other weak acids and bases
dissolved in it.
• The procedure of non-aqueous titration is very useful
because it satisfies two different requirements, namely
– suitable titration of very weak acids or bases along
with providing a solvent with an ability to dissolve
organic compounds.
• An example of a reaction in which water is not a
suitable solvent is the reaction given by:
R-NH2 + H+ ⇌ R-NH3
+
• which is competed with in an aqueous solvent by the
reaction given by:
H2O + H+ ⇌ H3O+

• This type of competition provided by water towards weak bases
or weak acids makes it difficult to detect the end point of the
titration.
• Therefore, these substances which have very sharp end points
when titrated in aqueous solutions due to their weakly basic or
weakly acidic nature generally need to be titrated in non-
aqueous solvents.
• Many reactions which occur in non-aqueous titration procedures
can be explained via the Bronsted-Lowry Theory and its
definition of acids and bases.
• Basically, acids can be thought of as proton donors, whereas
bases can be thought of as proton acceptors.
• It can also be noted that potentially acidic substances can
behave as acids only when a base (to which a proton can be
donated) is present.
• The converse of this statement also holds true, i.e. potentially
basic substances can behave as bases only when an acid (from
which a proton can be accepted) is present.

Need of Non-aqueous Titrations
• Non- aqueous titration has following needs -
1. It is useful for the titrations of very weak acids or bases.
2. Many organic acids which are insoluble in water, can be
dissolved in non-aqueous solvents. Thus, titration of
these organic acid is very easy.
3. It can be used for titration of mixture of acids as well.
4. These titrations show sharp end point with internal
indicator.
5. It is simple, qualitative and selective method.
6. It is a highly accurate method.

Types of Non aqueous solvent:
1) Aprotic solvents— are neutral, chemically inert
substances.
• They have a low dielectric constant, do not react
with either acids or bases and therefore do not
favor ionization.
• Examples– benzene, toluene, carbon tetrachloride,
chloroform etc.
2) Protophilic Solvents – These are basic in nature
and react with acids to form solvated protons
(Solvated proton Conjugate base of acid).
• A strong protophilic solvent changes the weak acids
to strong acids this is known as levelling (limited)
effect.
• Examples – liquid ammonia, amines, ether, pyridine,
etc.

3) Protogenic Solvents – These are acidic substances
and readily donate the proton.
 These are used to increase basicity (enhance basic
strength) of weak base. They show a levelling effect on
bases.
 They have a high dielectric constant, & react with bases
and therefore favor ionization.
 Examples- sulfuric acid, formic acid, H2S, acetic
anhydride, propanoic acid etc.
4) Amphiprotic solvents have both protophilic and
protogenic properties.
 They are dissociated to a slight extent.
 The dissociation of acetic acid, which is frequently used
as a solvent for titration of basic substances.
 Examples are acetic acid and the alcohols.

3. PRECIPITATION TITRATION
• Precipitation titration: it is titrimetric method in which
the titrant reacts with analyte and forms an insoluble
substance called precipitate. It continues till the last
amount of analyte is consumed.
• Principle: In the precipitation titration the quantity of
reagent added is equal to the precipitate.
• Quantity of reagent added = quantity of the
precipitate obtained
• Reactions involved in the process is given below:
AgNO3 + Cl- → AgCI + NO3
-

• Precipitation Titration Example
• Example – To determine the concentration of
chloride ion in a certain solution we can titrate this
solution with silver nitrate solution (whose
concentration is known). The chemical reaction
occurs as follows:
AgNO3 (aq) + KCl (aq) → AgCl (s) + KNO3.
Ag+(reagent) Cl–(solution) White ppt
• AgCl in the form of a white precipitate can be
seen settled at the bottom of the flask during
titration.
• The quantity of silver ion used to equivalence
point is equal to the quantity of chloride ion
which was originally present.

• Requirement of Precipitation Titration:
1. The precipitate formation is stoichiometric.
2. To allow the titrant to be added quickly, the
equilibrium between ppt & its ions in solution
much attained rapidly.
3. The ppt must be of low solubility in the solution.
This is indicated by small equilibrium constant
(Ksp).
4. A method to detect the stoichiometric point of
titration must be available. Best method for
detecting end point in ppt titration is by
• Argentometric Titration
• The word argentometric is taken from latin word
argentum i.e. Symbol of silver (Ag).

• It is a type of precipitation titration which involves
the use of silver ion, So ppt titration is also
referred as argentometric titration.
• A solution of silver nitrate of known concentration
is titrated against the chloride, Br, I, sample
solution.
Types of Precipitation Titration
• There are mainly three types of precipitation
titrations:
1. Volhard’s Method
2. Fajan’s Method
3. Mohr’s Method

1. Volhard’s Method
 This method was first given by German Chemist,
Jacob Volhard in 1874.
o The ppt titration in which Ag+ ion is precipitated by SCN-
(thiocynate ions) in presence of ferric (Fe3+) ions indicator
in acidic medium is called volhard method.
o This method involves the determination of halide (F, Cl, Br,
I) ions, anions (phosphate, chromate) in acidic medium by
using silver ions (obtained from AgNO3).
o In this method 1st analyte (halide ion solution or any other
anionic solution) is titrated with measured excess of
AgNO3.
Reaction 1 – If analyte contains chloride anions. The
reaction will be as follows -
• Cl- + Ag+ -------- AgCl + Ag+ (in excess)
• Now the unreacted or in excess silver ions are titrated
with standard solution of KSCN solution using iron ion
(Fe+3) as indicator.

Reaction 2 – The reaction can be shown as follows-
• Ag+ + SCN- -------- AgSCN .
• Now as the thiocyanate ion will be in excess in the
titration mixture react with indicator Fe3+ which gives
red color in the end point due to formation of
FeSCN(II) compound.
Reaction 3 – Reaction involved can be shown as
follows –
• Fe+3 + SCN- -------- FeSCN+2
(Red colored compound)
• It is an indirect method of precipitation.
• This titration must be performed in acidic medium to
avoid the formation of ferrous hydroxide.
• Iron ion is used as indicator in Volhard’s method.

• Advantages of Volhard’s Method:
1. The acidic environment give advantage for
halide analysis becoz anions do not form ppt
with Ag in acidic medium & will not interfere with
halides.
2. Give accurate results due to back titration.
• Limitation of Volhard’s Method: :
1. Cannot be used in neutral / basic medium.
2. It is time consuming.

2) Fajan’s Method
• This method was given by American chemist
Kazimierz Fajan. That’s why it is known as fajan’s
method.
• The ppt titration in which Ag+ ions is titrated with
halides/ thiocynate ions in presence of adsorption
indicator is called as fajan’s method
• This method is also known as indicator adsorption
method.
• In this method dichlorofluorescein/ fluorescein is
used as an indicator which get adsorb onto surface of
silver salt ppt at the end point & this adsorption causes
a change in color of indicator.
• Adsorption indicator is weakly acidic & act as anion in
solution.

 In chloride solution, due to excess of Cl- ion they form
=Primary layer
 Second layer form by sodium cations & excess of silver ion
attracts the indicator to form next layer.
 The end point is determined when indicator act with excess
of AgCl and turns to Reddish colour complex of AgCl
and indicator.

• Reaction – reaction involved can be written as
follows –
1) AgNO3 + Cl-  AgCl + NO3
-
(in solution of NaCl) (White ppt)
2) Ag+ + Fl - (Indicator) -------- AgF (Silver fluoride complex)
Reddish colour
• Indicator is weakly acidic & pH of solution should be
slightly alkaline to keep indicator in anion form.
• It is a direct method of precipitation.

3) Mohr’s Method
• This method was given by Karl Friedrich Mohr, a German
Chemist. So it is called as Mohr’s method.
• A precipitate titration in which silver ion is used as titrant
and chromate ion is used as indicator is called as mohr’s
method.
• It’s a direct titration method.
• A precipitate titration in which chloride ion solution used as
analyte & Potassium chromate (K2CrO4) is used as
indicator.
• It is used for halides determination.
• At the end point, when all chloride ions are consumed by
silver ion, reddish brown colored precipitate is formed by
reaction of silver ion and chromate ion.

Reaction- Reaction involved can be written as
follows –
• AgNO3 + Cl- --------- AgCl + NO3
-
(in solution of NaCl) (White ppt)
• At the end point –
• 2Ag+ + CrO4
-2 ---- Ag2CrO4 (Silver chromate)
(Reddish Brown ppt)
• In this method neutral medium (i.e. pH= 7) is used
becoz
1. In acidic medium= Chromate ---- H2CrO4 &
end point is delayed
2. In basic medium = Salt formation -- AgOH

4. Complexometric Titration / chelatometry
• These are the titration in which specific metal ion
(e- acceptor) is transformed into coloured complex
by addition of chelating agent (e- donor) .
• Complexometric Titration is used in the detection of
mixtures of different metal ions present in the
solution.

• The equivalent point can be identified very accurately using a
complexometric titration.
• EDTA is used as a titrant and it is pretty much well established.
• Important Term
1. Complex is formed by reaction of metal ion (M+) wither either
anion or neutral molecule.
2. Metal ion is known as central metal atom= act as lewis acid
(e- acceptor)
3. Anion / neutral molecule known as ligand (L) = act as lewis
base (e- donor)
4. Chelates are insoluble= water
Soluble = organic solvent
5. Sequestering agent- ligands which form water soluble chelates.
Eg= EDTA
6. Co-ordinate bond= bond formed between central metal atom
(ion acceptor) & Ligand (donor)

• EDTA Complexometric Titration
1. EDTA called as ethylene diamine tetra-acetic acid is a
complexometric indicator consisting of 2 amino groups
and four carboxyl groups called as Lewis bases.
2. Edta is a hexadentate ligand because of its competence
to denote six pair of lonely electrons due to the formation
of covalent bonds.
3. Even the presence of small metal ions would lead to a
distinct change in the color. This leads to the formation of
a weak complex.
4. Complexing agents are less soluble in water, and most of
them are free acids.
5. They are used in volumetric Solutions. Before using
them, they are converted into sodium salts that are
feasible in water.

6. Since they are characterised with less solubility in water,
they are used for titration.
7. Sometimes simple titration methods are used to determine
the simple metal ions present in water.
8. But to determine the exact number of metal ions present
complexometric titration is used, and it is conducted using
EDTA.

Principle
• Indicator Eriochrome Black T (EBT) becomes wine
red in color when binds with metal ions while remain
blue in color when free from metal ion.
• While EDTA (which is ethylene diamine tetra acetic
acid) is colorless whether its bound to metal ion or
not.
• So, addition of EBT indicator in the sample (water
containing metal) makes it wine red in color as
eriochrome black T binds with metal ions.
• Eriochrome black T binds with metal ions loosely
while EDTA binds with metal ions strongly.
• So, when all metal ions are bound to EDTA,
indicator EBT remain free in the sample and
solution turns blue.

• Metal salt + Indicator ------- Metal salt –Indicator complex
(Weak complex) (wine red)
• Metal salt –Indicator complex (Weak complex) + EDTA
(titrant)---- Metal salt- EDTA complex (comparatively strong)
+ Indicator free form (blue).

Types of Complexometric Titration
• EDTA can be used as chelating titrant. EDTA titrations can be
performed in many ways. Few of them are given as follows –
1. Direct Titration-
• In this titration standard EDTA solution is added to given
sample containing metal ions solution in presence of
buffers.
• Copper, barium, zinc, mercury, aluminum, lead, bismuth,
chromium etc. are metals which can be determined by
using direct complexometric titration.
2. Back Titration –
• In this titration excess amount of standard solution of EDTA
is added to the metal solution being examined. Then excess
amount of EDTA is back titrated by standard solution of
second metal ion for eg- Mg2+ , Zn2+.
• EBT is used as indicator.

3. Replacement Titration –
• It is used when direct titration or back titration don’t
give sharp endpoints.
• In this analyte (containing metal) is added in metal-
EDTA complex. Metal present in analyte displaces
another metal from metal-EDTA complex.
4. Indirect Titration / alkalimetric titration –
• It is used for determination of anions, which do not
react with EDTA.
• Protons from disodium EDTA are displaced by a heavy
metal & titrated with sodium alkali.

 Indicators used:
• Organic dyes such as fast sulphone black,
Eriochrome black T, Eriochrome red B, Patton
Reddder, Murexide, etc.
• The endpoint detection in complexometric titration
can be done by two methods.
1. Visual Method
• One of the most common methods for
determination of endpoint owing to its simplicity,
least cost and accuracy.
• Following are some of the visual methods used for
determining the end point of the complexometric
titrations.
a) Metallochromic or PM indicators
b) pH indicators
c) Redox indicators

2. Instrumental Method
• Use of visual methods in determining the endpoint
is not free from limitations including inaccuracy or
human visual errors.
• Some instrumental techniques used in endpoint
determination are
a) Photometry
b) Potentiometry
c) Miscellaneous methods.

1. Masking agent :
• A masking agent is a reagent used in chemical
analysis which reacts with chemical species that may
interfere in the analysis.
• Eg- KCN, triethanolamine, Fluoride, Iodide.
2. Demasking agent :
• Demasking is the process in which the masked
substance regains its ability to enter into a particular
reaction.
• Eg: the masking of CN- can be removed by:
• Mixture Formaldehyde-acetic acid
• On addition of demasking agent [Zn(CN)4]2-, Zn is
liberated.

5. REDOX
 Redox reactions are those chemical reactions in which
both oxidation as well as reduction occur simultaneously.
 The redox titration often needs a redox indicator or a
potentiometer.
 Redox titration depends on an oxidation-reduction reaction
that occurs between the analyte and the titrant. It is also
one of the most common methods for identifying the
concentration of the analytes that are unknown.

Principle of Redox Titration
• Redox reactions consist of both oxidation and
reduction reactions.
• The primary features of these reactions are as
follows:
 Reduction Reaction
• A substance undergoes a reduction in the following
ways:
• Addition of hydrogen atom
• Removal of the oxygen atom
• Accepting electrons
• Reduction in the oxidation state of the substance
 Oxidation Reaction
• A substance undergoes oxidation in the following
ways:
• Addition of oxygen

• Removal of hydrogen
• Loss of electrons
• An overall increase in the oxidation state of the
substance
Definition:
 Oxidation is defined as the loss of electrons by a
chemical species (atom, ion or molecule).
 Reduction is the gain of electrons by a chemical
species (atom, ion or molecule).
 An oxidising agent that chemical species which takes
electrons thus it is an electron acceptor.
 A reducing agent is the chemical species that gives
electrons and thus acts as an electron donor.

Detection of End Point in Redox Tiration:
A) Self-Indicator:
• A few titrants, such as Potassium permanganate ( KMnO4) is an
oxidising agent (O.A.), which is of deep voilet color.
• Used in Redox Tiration– it get reduced into brown colour Mn2+
ion (In acidic solutions) at end point & can be detected.
B) External Indicator:
• Dichromate is an O.A. , which is of deep purple color.
• Ferrous ions species that is oxidized when mixed with K2Cr2O7
& electrons are eliminated.
C) Internal Redox Indicator -The reducing agents contains the
electrons that are transferred during the reaction, so it is in its
reduced from, which we will designate Red. Transferring the
electrons converts it to its oxidized form, which we will call ox.
Inox + ne- ⇌ Inred

D) Irreversible Titration:
 Some highly colored organic compounds that undergo
irreversible oxidation or reduction.
 Eg- Methyl orange & Methyl red

 Oxidizing Agents:
1. Potassium permanganate
2. Potassium dichromate
3. Iodine
4. Potassium iodate
5. Bromate-bromide mixture
 Reducing agent:
1. NaH
2. LiH
3. LiAlH4
4. CaH2

Oxidation with Potassium permanganate
 KMNO4 is a strong OA in acidic medium:
2KMnO4 + 3H2SO4 → 2MnSO4 + K2SO4 + 5O2 + 3H2O
• HCl is not used instead of H2SO4 as it is oxidized to
Chlorine in presence of permanganate
• 2KMnO4 + 16HCl → 2MnCl2 + 2KCl + 5Cl2 + 8H2O
• In strong alkaline medium, heptavalent manganese is
reduced as follow:
2KMnO4 → 2MnO2 + K2O
•
• Manganese dioxide – black colour & mask end point.
Manganese
dioxide
Potassium
sulphate
Manganese
sulphate
Potassium
permanganate
Manganese
Chloride

Titration/ Standardization of Potassium
Permanganate against Oxalic Acid
o Prepare a standard Oxalic acid solution of about
250 ml.
o The molecular mass of oxalic acid is calculated by
adding the atomic mass of each constituent atom
o The molecular mass of H2C2O4.2H2O = 126
o Since the weight of oxalic acid that is required to
make 1000 ml of 1M solution is 126 g. Hence, the
weight of oxalic acid needed to prepare 250 ml of
0.1 M solution = 126/1000 x 250 x 0.1 = 3.15 g

Determining the Strength of KMnO4 using Standard
Oxalic Acid Solution:
• In this titration, the analyte is oxalic acid and the titrant is
potassium permanganate.
• The oxalic acid acts as a reducing agent, and the
KMnO4 acts as an oxidizing agent.
• Since the reaction takes place in an acidic medium, the
oxidizing power of the permanganate ion is increased.
This acidic medium is created by the addition of dilute
sulfuric acid.
• MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
• KMnO4 acts as an indicator of where the permanganate
ions are a deep purple colour.
• In this redox titration, MnO4– is reduced to colourless
manganous ions (Mn2+) in the acidic medium.

• The last drop of permanganate gives a light pink
colour on reaching the endpoint.
• The following chemical equation can represent
the reaction that occurs.
Molecular equation
• 2KMnO4 + 3H2SO4 → K2SO4 + 2MnSO4 +
3H2O + 5[O]
• H2C2O4.2H2O + [O] → 2CO2 + 3[H2O] × 5
Complete Reaction
• 2KMnO4 + 3H2SO4 + 5 H2C2O4.2H2O → K2SO4 +
2MnSO4 + 18H2O + 10CO2

 Ionic equation
 MnO4- + 8H+ +5e- → Mn2+ + 4 [H2O]×2
 C2O42 - → 2CO2 + 2e- × 5
 Complete Reaction
 2MnO-4 + 16H+ + 5C2O4 2- → 2Mn2+ + 8H2O +
10CO2
 From the above-balanced chemical reaction, it can
be observed that 2 moles of KMnO4 reacts with 5
moles of oxalic acid.

B. Gravimetric analysis
o Gravimetric analysis is a technique through which the
amount of an analyte (the ion being analyzed) can be
determined through the measurement of mass.
 The principle of Gravimetric Analysis:
 The principle behind the gravimetric analysis is that the
mass of an ion in a pure compound can be determined.
Later, used to find the mass percent of the same ion in a
known quantity of an impure compound.

• Steps in a gravimetric analysis
After appropriate dissolution of the sample the following steps
should be followed for successful gravimetric procedure:
1. Preparation of the Solution:
• This may involve several steps including adjustment of the pH of
the solution in order for the precipitate to occur quantitatively and
get a precipitate of desired properties, removing interferences,
adjusting the volume of the sample to suit the amount of
precipitating agent to be added.
2. Precipitation: This requires addition of a precipitating agent
solution to the sample solution. Upon addition of the first drops of
the precipitating agent, supersaturation occurs, then nucleation
starts to occur where every few molecules of precipitate aggregate
together forming a nucleus. At this point, addition of extra
precipitating agent will either form new nuclei or will build up on
existing nuclei to give a precipitate.

This can be predicted by Von Weimarn ratio
where, according to this relation the particle size
is inversely proportional to a quantity called the
relative supersaturation where
 Relative supersaturation = (Q – S)/S
 The Q is the concentration of reactants before
precipitation, S is the solubility of precipitate in the
medium from which it is being precipitated.
Therefore, to get particle growth instead of further
nucleation we must make the relative
supersaturation ratio as small as possible. The
condition needs to be adjusted such that Q will be
as low as possible & S will be relatively large.

3. Digestion of the precipitate:
• The precipitate is left hot (below boiling) for 30 min to
one hour for the particles to be digested.
• Digestion involves dissolution of small particles and
reprecipitation on larger ones resulting in particle
growth and better precipitate characteristics.
• This process is called Ostwald ripening.
• An important advantage of digestion is observed for
colloidal precipitates where large amounts of
adsorbed ions cover the huge area of the precipitate.
• Digestion forces the small colloidal particles to
agglomerate which decreases their surface area and
thus adsorption

4. Washing and Filtering the Precipitate:
 It is crucial to wash the precipitate thoroughly to remove all
adsorbed species.
 One should be careful nor to use too much water since part
of the precipitate may be lost.
 in case of colloidal precipitates we should not use water as
a washing solution since peptization would occur. In such
situations dilute nitric acid, ammonium nitrate, or dilute
acetic acid may be used.
5. Drying and Ignition:
 The purpose of drying (heating at about 120-150oC in an
oven) or ignition in a muffle furnace at temperatures
ranging from 600-1200oC is to get a material with exactly
known chemical structure so that the amount of analyte
can be accurately determined.
 The ppt is converted to more chemically stable form.

6. Weighing the ppt :
 The ppt cannot be weighed accurately if placed
on filter paper, nor can the ppt be completely
removed from filter paper in order to weigh it.

• Types of Gravimetric Analysis
• There are 4 fundamental types of gravimetric analysis.
1. Volatilization gravimetry
• Volatilization Gravimetry involves separating components of our
mixture by heating or chemically decomposing the sample.
2. Precipitation gravimetry
• Precipitation Gravimetry uses a precipitation reaction to
separate one or more parts of a solution by incorporating it into
a solid.
3. Electrogravimetry
• Electrogravimetry is a method used to separate and quantify
ions of a substance, usually a metal.
4. Thermogravimetric
• Thermogravimetric is a method of thermal analysis in which
changes in physical and chemical properties of materials are
measured as a function of increasing temperature or as a
function of time.

• Advantages of the Gravimetric Method
1. It is precise and accurate when using modern analytical
balance.
2. Gravimetric analysis can also be used to determine the
atomic masses of many elements up to the extent of six-figure
accuracy.
3. Gravimetry provides only very little room for instrumental error
and it also does not require a series of standards for
calculating the unknown.
• Disadvantage of Gravimetric Method:
1. The gravimetric analysis, in general, can provide analysis of a
single element, or a limited group of elements, at a time.
2. The chief disadvantage of this method is that it is very time-
consuming.
3. The chemist in today's world prefers other methods over this
method.
4. minor misstep in a procedure can often mean tragedy for the
analysis

Volumetric analysis

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Volumetric analysis

Ähnlich wie Volumetric analysis (20)

Mehr von ShaliniBarad

Mehr von ShaliniBarad (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Volumetric analysis