1. This document discusses various oxidation-reduction titration methods including those using ceric ammonium sulfate, potassium iodate, potassium bromate, and titanous chloride as titrants.
2. Preparation and standardization procedures are provided for 0.1N ceric ammonium sulfate, 0.05M potassium iodate, 0.1N potassium bromate, and titanous chloride solutions.
3. Examples of titrations discussed include assays of ferrous fumarate, acetomenaphthone, ferrous gluconate tablets using ceric ammonium sulfate; assays of benzalkonium chloride and hydralazine hydrochloride using potassium iodate; and assays
♛VVIP Hyderabad Call Girls Chintalkunta🖕7001035870🖕Riya Kappor Top Call Girl ...
Redox titration for mpharm ist year
1. 1
A SEMINAR ON OXIDATION
REDUCTION TITRATIONS
CERRIC AMMONIUM SULPHATE
POTASSIUM IODATE/POTASSIUM BROMATE
TITANOUS CHLORIDE
EXAMPLES OF DRUGS IN I.P1996
2. 2
INTRODUCTION
Oxidation reduction titration is a part of titrimetric analysis in which we
can find out the quantity of pure component, based on the
measurement of volume of standard solution and this measurement
of volume of standard can be possible in case of reaction, if this
reaction is oxidation reduction then this method is called as oxidation
reduction titration or redox titration.
Oxidation reduction reaction:-
Oxidation reduction reactions are chemical processes in which change in
valency of reacting element takes place.
1) Oxidation
Oxidation is defined as loss of electron to give higher oxidation state.
E.g. : Fe++ →Fe+++ + e-
3. 3
2) Reduction
Reduction is defined as gain of electron to give lower oxidation state.
E.g. Fe+++ + e- → Fe++
In Oxidation reduction reaction, oxidation and reduction are occurs
simultaneously.
Ox1 + Red2 ⇋ Red1 + Ox2
Here, Ox1 is oxidizing agent and Red2 is reducing agent
In above reaction Ox1 get reduce to give Red1
Red2 get oxidize to give Ox2.
Hence we can say that an oxidizing substance will take an electron
and reduce to lower state.
M a+ + ne- → M (a - n) (+)
Also reducing substance will tend to give electron and get oxidized
M a+ → M (a + n) + ne-
4. 4
INDICATORS USED IN REDOX TITRATIONS
Redox indicators are themselves an oxidant or reductant. Oxidized form has
one colour and reduced form has other colour. When slight excess of
oxidant is present, the indicator changes its colour and is shown as end
point of the titration.
TYPES
• Self indicators
• External indicators
• Internal indicator
• Instrumental techniques
1. Self indicators
The oxidised or reduced form of the titrant or the substance itself is self
indicating. Eg. Cerric ions are yellow coloured and are reduced to colorless
ions before the end point. The end point is shown by the yellow colour due
to excess of cerric ions. (Other self indicators are potassium permanganate
which is pink and Iodine which is brown at the end point respectively)
5. 5
2.External indicators
Instead of adding indicator to the titration solution itself, few drops of the
solution is removed periodically, placed on a tile and mixed with indicator
solution. This shows a colour change of indicator. eg. In the titration of
ferrous ions with potassium dichromate, before the end point, few drops of
titrating solution (ferrous ions) gives deep prussian blue colour with
potassium ferricyanide.
3. Internal indicators
As mentioned earlier, the redox indicator itself represents a redox system with a
redox potential which is intermediate between that of the titrated substance and
the titrant. An example of such indicator is orthophenanthroline-ferrous complex.
4. Instrumental technique
By using potentiometer or conductometer. the end point can be determined. In
conductometer. a platinum electrode is used. But the determination of end point
is difficult as sharp results are not obtained.
6. 6
Redox indicators
Indicators Colour change
Oxidised Form Reduced form
ferroin Pale blue red
Diphenyl benzidine Violet Colourless
Diphenyl amine Violet Colourless
Nitro ferroin Pale blue red
2.6-dibromo phenol indophenol Blue Colourless
2.6-dibromo phenol indophenol Blue Colourless
2.6-dibromo phenol indophenol Blue Colourless
7. 7
CERRIC AMMONIUM SULPHATE TITRATION METHODS
Cerric ammonium sulphate serves as a powerful oxidizing agent in
an acidic medium. The salt has a bright yellow colour. On reduction,
the resulting cerric salt obtained is colourless in appearance and
therefore, strong solutions may be consider as self indicating. The
oxidation reactions involved may be expressed as follows.
Ce4+ + e → Ce3+
ADVANTAGES
Solutions remain fairly stable even when boiled and no need to
protect from light
Solutions quantitatively react with either arsenite or oxalate
[(COO)2]2- ion, and there fore, either arsenic trioxide or sodium
oxalate may be employed as a primary standard.
cerric ion Ce 3+ is colourless and hence offers no interference with
the indicator end-point.
8. 8
Preparation of 0.1 N Cerric Ammonium Sulphate solution
Materials Required:
Cerric ammonium sulphate:65 g
sulphuric acid (conc.) 30 ml.
Procedure:
Dissolve 65 g of Cerric ammonium sulphate, with the help of gentle
heat, in a mixture of 30 ml of sulphuric acid and 500 ml distilled
water. Cool, filter the solution through a Fine porosity sintered-glass
crucible, dilute to 1 litre mark in a volumetric flask and mix thoroughly.
Standardization of 0.1 N Cerric Ammonium Sulphate Solution
Materials Required:
Arsenic trioxide: 0.2 g , NaOH solution (8.0% w/v) 25 ml, dil. sulphuric
acid (10% w/v) 30 ml, osmic acid solution (1.0% w/v in water) 0.15
ml, ferroin sulphate solution
9. 9
Procedure:
Weigh accurately about 0.2 g of arsenic trioxide previously dried at
105 0.C for 1 hour and transfer to a 500 ml conical flask. Wash down
the inner walls of the flask with 25 ml of sodium hydroxide solution,
swirl to dissolve, add 100 ml of water and mix. Add 30 m1 of diluted
sulphuric acid, 0.15 ml of osmic acid solution, 0.1 ml of ferroin
sulphate solution and slowly titrate with cerric ammonium. sulphate
solution until the pink colour is changed to a very pale blue.
Each ml of 0.1 N cerric ammonium sulphate is equivalent to 0.004946
g of arsenic trioxide.
Reaction: - As2O3 + 6NaOH → 2Na3AsO3 + 3H2O
2Ce (SO4)2 + Na3AsO3 + H2O → Ce2 (SO4)3 + Na3AsO4+ H2 SO4
10. 10
Ex. Of . CERRIC AMMONIUM SULPHATE TITRATION
1. Assay of Ferrous Fumarate
Materials Required:
Ferrous fumarate 0.3 g, diluted H2S04 (10% w/v)15 ml, ferroin
sulphate solution; 0.1 N cerric ammonium sulphate solution.
Procedure:
Weigh accurately about 0.3 g of ferrous fumarate and dissolve
in 15 ml of dilute sulphuric acid by the help of gentle heating.
Cool, add 50 ml of water and titrate immediately with 0.1 N
cerric ammonium sulphate, employing ferroin solution as
indicator.
Each ml of 0.1 N cerric ammonium sulphate is equivalent to
0.01699 g of C4H2FeO4
11. 11
2) Acetomenaphthone
Materials Required:
Acetomenaphthone 0.2g, gla CH3COOH 15ml, dil HCl (10% w/v) 15
ml, cerric ammonium sulphate 0 .05 N; ferroin sulphate solution.
Procedure:
Weigh accurately about 0.2 g of acetomenaphthone and boil it with
15 ml of glacial acetic acid and 15 ml of dilute hydrochloric acid
under a reflux condenser for 15 minutes. Cool the contents carefully
and taking adequate precautions to avoid any atmospheric
oxidation. Add 0.1 ml of ferroin sulphate solution as indicator and
titrate with 0.05 N cerric ammonium sulphate. Repeat the assay
without the substance being examined (blank determination) and
incorporate the correction, if any.
Each ml of 0.05 N cerric ammonium sulphates is equivalent to 0.006457 g
of C15H14O4
13. 13
Ferrous gluconate tablets
Assay: -
Powder 20 tablets, wt accurately a quantity of the powder
equal to 1g of ferrous gluconate dissolve in mixture of 140
ml of water and 60 ml of 1ml sulphuric acid and titrate with
0.1m cerric ammonium sulphate using ferroin solution as
indicator until red color disappeared.
Each ml of 0.1 ml cerric ammonium sulphate is equivalent
to 0.04822 g of ferrous gluconate .
14. 14
2 ) TITRATIONS WITH POTASSIUM IODATE
Potassium iodate is a fairly strong oxidizing agent that may be used
in the assay of a number of pharmaceutical substances. The
oxidation-reduction methods with potassium iodate invariably based
on the formation of (ICI) in a medium of hydrochloric acid solution.
Preparation of 0.05 M Potassium Iodate
potassium iodate is dried to a constant weight at ll0oC to free from
moisture and then brought to room temperature in a desiccator. KIO3
is a very stable salt and may be obtained in a very pure form.
Therefore, it is possible to prepare the standard solutions of KIO3 by
dissolving the calculated weight of the salt in water and diluting the
same to an approximate volume.
Procedure: Weigh accurately 10.7 g of pure potassium iodate,
previously dried at ll0°C to weight, insufficient DW to produce 1 litre in
a volumetric flask.
15. 15
Standardiosation of potassium iodate solution
Potassium iodate is primary standard hence, the standard solution
can be prepare by direct weighing ,due to high purity of KIO3 ,
potassium iodate can be standardised by following method.
Procedure
Dil. 25 ml of KIO3 solution to 100 ml and add 2g of KI2 and 10ml of
1m H2SO4 then titrate with 0.1 m sodium thiosulphate and 1ml starch
solution added towards the end of titration.
Each ml of 0.1 m sodium thiosulphate is equivalent to 0.03566 g of
KIO3.
16. 16
Ex.
1) Benzalkonium Chloride
Procedure:
Weigh accurately Benzalkonium chloride 4.0 g and dissolve it in sufficient D.W
to make 100ml, Pipette 25.0 ml into a separating funnel, add 25 ml of CHCl3, l0
ml of 0.l N NaOH and l0ml of potassium iodide solution. Shake the contents
thoroughly, allow to separate and collect the chloroform layer in another
separating funnel. Treat the aqueous layer with 3 further quantities each of 10
ml of chloroform discard the chloroform layer. To the aqueous layer add 40 ml of
hydrochloric acid, cool and titrate with, potassium iodate till the solution
becomes pale brown in colour. Add 2 ml of chloroform and continue titration until
the chloroform layer becomes colourless. Titrate a mixture of 29 ml of water, 10
ml KI solution and 40 ml of hydrochloric acid with 0.05M potassium iodate under
identical conditions (Blank titration). The differences between the titrations
represent the amount of 0.05 M potassium iodate required.
Each ml of 0.05 M potassium iodate is ~ to 0.0354 g of C22H40CIN.
17. 17
Hydralazine hydrochloride injection
Assay :-
Dissolve 0.1 g of mixture content of 25 ml water and 35 ml HCl
and carry out the method for potentiometric titration using 0.05
M potassium iodate and platinum indicator electrode and
calomel as a reference electrode .
Each ml of 0.05 m KIO3 is equivalent to 0.009832 g of
hydralazine hydrochloride
18. 18
TITRATIONS WITH POTASSIUM BROMATE
Potassium bromate is an oxidizing agent and use in the assay of a
number of pharmaceutical substances, namely: mephenesin, phenol,
and sodium salicylate. This particular method solely depends upon
the formation of iodine monobromide (IBr) in relatively higher
concentration of hydrochloric acid solution.
Preparation of 0.1 N Potassium Bromate
Procedure:
Weigh accurately 2.784 g of potassium bromate into a beaker and
dissolve it in sufficient distilled water. Transfer the solution
quantitatively into a 1 litre volumetric flask.
19. 19
Standardization of 0.1 N Potassium Bromate Solution
Potassium bromate is primary standard hence, the standard solution
can be prepared by direct weighing due to high purity. solution may
be standardized by following method.
Procedure:
Transfer an accurately measured volume of about 30.0 ml of 0.1 N
potassium bromate solution into a 250 m1 iodine flask. Add to it 3.0 g
potassium iodide, followed by 3.0 m1 of hydrochloric acid. Mix the
contents thoroughly and allow it to stand for 5 minutes with its
stopper in position. Titrate the liberated iodine with previously
standardized 0.1 N sodium thiosulphate, using 3.0 ml of freshly
prepared starch solution as an indicator at the end-point. Carry out a
blank run using the same quantities of the reagents and incorporate
the necessary corrections, if any.
Each ml of 0.1 N sodium thiosulphate is equivalent to 0.002784 g of KBr03
21. 21
Procedure:
Weigh accurately 0.15 g of mephenesin and dissolve in 50 m1 of DW
into a 250 m1 iodine flask. Add to it 25.0 m1 of 0.1 N potassium
bromate solution and 10.0 g of powdered potassium bromide. After
the dissolution of KBr, add 10 m1 of hydrochloric acid, insert the
moistened stopper, and after 10 seconds add 10 m1 of potassium
iodide solution. Titrate with 0.1 N sodium thiosulphate using starch
solution as indicator.
Each m1 of 0.1 N potassium bromate is equivalent to 0.00911 g of
Cl0H14O3.
23. 23
Procedure:
Weigh accurately 0.5 g of phenol and dissolve in sufficient water to
produce 500 m1 in a volumetric flask. Mix 25.0 ml of this solution with
25.0 ml of 0.1 N potassium bromate in a 250 ml iodine flask and add
to it 1 g of powdered KI and 10.0 ml of dilute hydrochloric acid.
Moisten the glass stopper with a few drops of KI solution and place it
in position. Set it aside in a dark place for 20 minutes while shaking
the contents frequently in between. Add to it 10 ml of KI solution,
shake the contents thoroughly and allow it to stand in the dark for a
further duration of 5 minutes. Wash the stopper and neck of the flask
carefully with DW, add 10 ml chloroform and titrate with the liberated
iodine with 0.1 N sodium thiosulphate using freshly prepared starch
as an indicator. Carry out blank titration and any necessary
correction, if required.
Each m1 of 0.1 N potassium bromate is ~ to 0.001569 g of C6H6O.H
24. 24
TITANOUS CHLORIDE TITRATION
PRINCIPLE:
The principle of Redox titrations applies
TYPES OF TITRATIONS
1 .Direct titration
2 .Back titration
1. DIRECT TITRATION:
Ferric salts, Azodyes, Quinones can be estimated by this method. This
method involves titration of the compound directly by Titanous chloride.
2. BACK TITRATION:
Determination involving the excess use of titanous chloride & back
titration with ferric ammonium sulphate
25. 25
TITANOUS CHLORIDE
• PREPARATION OF 0.1N TITANOUS CHLORIODE SOLUTION
• STANDARDISATION OF 0.1 N TITANOUS CHLORIDE SOLUTION
APPLICATIONS:
A] Use full in the titrations of dyes/estimation of dyes
•Methylene blue
•Indigo
•Crystal violet
•Eosin
•Malachite green
•Magenta
•Orange G
•Brilliant green
B] It is used in the estimation of ferric salts.
C] It is used in the estimation of nitro compounds.
D] It is used in the estimation of quinones
28. 28
Procedure:
weigh accurately 0.5 g, dissolve in a mixture of 10ml of water & 50ml
of 1M H2SO4 .Boil under reflux for 1 hour, cool & dilute to 100ml with
water. pipette out 20ml from this solution add 40ml of H2O, 40g ice
,15ml of 2M HCl & 0.1ml of ferroin solution & titrate with 0.1M cerric
ammonium sulphate until a yellow color is produced. Perform blank
titration.
1ml of 0.1M of cerric ammonium sulphate ~ 0.00756g of
paracetamol
29. 29
FERROUS SULPHATE [ FESO4,7 H2O]
Principle:
2 FeSO4 + 2 Ce(SO4)2,2(NH4)2SO4 Fe2SO4 + 2NHCe(SO4)2 + 6NH3
+ 3 H2SO4
Procedure: Weigh accurately about 1g, dissolve in a mixture of 30ml water + 20ml
dil H2SO4 and titrate with 0.1N cerric ammonium sulphate using ferroin sulphate
solution as indicator. End point will be red to light blue.
1ml of 0.1N cerric ammonium sulphate ~ 0.0278 g of ferrous sulphate
POTASSIUM IODATE TITRATIONS
1. POTASSIUM IODIDE
Principle:
IO3
- + 5I- + 6H+ 3I2 + 3H2O
IO3
- + 6 H+ + 4 e- 3 H2O + I+
5 I+ + 5 Cl- 5 ICl
KIO3 + 2 KI + 6 HCl 3 KCl + 6 ICl + 3 H2O
30. 30
Procedure:
Accurately weigh about 0.35g, dissolve in about 10ml of water, add 35 ml of HCl,
5ml of CHCl3, titrate with 0.05m KIO3 until the purple color disappears from the
CHCl3. Add the last drops of the iodate followed by shaking after each drop, allow
standing for 5mins. If any color develops in CHCl3 layer continue till the chloroform
layer becomes colorless.
Each ml of 0.05M potassium iodate ~ 0.0166g of potassium iodide
SODIUM DIATRIZOATE INJECTION:
Procedure:
Take 0.5g of sample in a glass stoppered conical flask, add 12ml of 5 M NaOH &
1g of zinc powder & boil under a reflux condencer for 30 mins, cool , rinse the
condencer with 30ml of water . Filter through cotton & wash the flask & filter with
with two quantities each of 20ml of water . To the combined filtrate & washings
add 80ml of HCl, cool & titrate with 0.05M KIO3 until the dark brown color
becomes pale brown ,add 5ml of CHCl3 & continue the titration , shaking well, after
each addition , until the CHCl3 becomes colorless.
Each ml of 0.05M potassium iodate ~ 0.02120g of sodium diatrizoate
31. 31
POTASSIUM BROMATE TITRATIONS
ISONIAZID
PRINCIPLE: KBrO3 + 5 KBr + 6 HCl 3 Br2 + 3 H2O + 6 KCl
PROCEDURE:
Weigh about 0.25g, dissolve in sufficient water to produce 100ml. Take 20ml of the
resulting solution, and add 100ml of water, 20ml of HCl, 0.2g of potassium bromide
titrate slowly with continuous shaking with 0.0167M potassium bromate solution.
Methyl red solution is used as indicator, end point is red color disappearence
Each ml of 0.0167M potassium bromate ~ 0.003429 g of Isoniazid
N
COOH
+ N2 +
N
CONHNH2
++ 2Br
2
H2
o 4HBr
33. 33
Procedures:
Dissolve the sample of 0.5 g, accurately in 100ml of water, add HCl of
100ml, heat to boiling and pass a current of CO2 through the solution.
Titrate with 0.1N Ticl3 until the clear blue color disappears, leaving a
reddish grey solution .
Each ml of 0.1N titanous chloride ~ 0.01599 g of methylene blue
REFERENCE
1. Pharmaceutical analysis by Ravishankar
pg-20-2,20-6,20-7
2. Pharmaceutical analysis by Beckett & stanlake
pg- 209,214,219,220
3. Indian pharmacopoeia 1996 edition
pg-317,408,554,609,692
4. practical pharmaceutical analysis by sonali sheory
pg-79,86,88,89
