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Ascorbic Acid Strength via Iodimetry

This document describes an iodimetric titration procedure to determine the strength of ascorbic acid by titrating a sample against a standard N/10 iodine solution. Iodimetric titrations involve using iodine as the oxidizing agent to titrate against a reducing agent like ascorbic acid. The endpoint of the titration is detected using starch solution, which turns from colorless to a permanent light blue color upon reaching the endpoint. The amount of iodine solution used is then used to calculate the amount and purity percentage of ascorbic acid in the given sample.

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Harsh Thakur
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835 views2 pages

Ascorbic Acid Strength via Iodimetry

This document describes an iodimetric titration procedure to determine the strength of ascorbic acid by titrating a sample against a standard N/10 iodine solution. Iodimetric titrations involve using iodine as the oxidizing agent to titrate against a reducing agent like ascorbic acid. The endpoint of the titration is detected using starch solution, which turns from colorless to a permanent light blue color upon reaching the endpoint. The amount of iodine solution used is then used to calculate the amount and purity percentage of ascorbic acid in the given sample.

Uploaded by

Harsh Thakur
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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IODIMETRIC TITRATION

Aim:To determine the strength of given ascorbic acid by titrating against standard N/10 iodine
solution.

Principle:
Iodimetric titrations are defined as those iodine titrations in which a standard iodine solution is used
as an oxidant and iodine is directly titrated against a reducing agent. Iodimetiric procedures are used
for the determination of reducing agents like thiosulphates, sulphites, arsenates and stannous
chloride etc. by titrating against standard solution of iodine taken in a burette.

The titration of a reducing agent such as ascorbic acid with iodine (I2 ,generally present as I3- ,
triiodide ion) to produce iodide ion (I -) is referred to as an iodimetric titration.

C6 H8 O6 + 2 H2O + I2 C6 H6 O6 + 2 I - + 2 H3 O +
Ascorbic acid (vit –C) excess

Reagents:
Standard N/10 Iodine, given ascorbic acid powder, 0.1 N H2SO4,freshly prepared 1% starch
solution

Apparatus:

Pipettes, burette, conical flask.

Procedure:
Clean the burette and fill with standard N/10 Iodine solution and note the initial reading.

Take 0.100gms of given ascorbic acid powder in a clean conical flask and dissolve it in 50 ml
freshly boiled & cooled distilled water (CO2 free distilled water).

Then add 0.1 N H2SO4 solution and 2ml of freshly prepared 1% starch solution.

Mix well and titrate with Iodine solution, swirling the titration flask after each addition of iodine
until a permanent light blue colour is just obtained.

This is the end point. Note the burette reading and repeat the titration until two concordant values
are obtained.

Observation:
Burette: N/10 standard Iodine solution
Pipette: solution of ascorbic acid

Indicator: Starch solution (freshly prepared)

Colour change:Colourless to blue

Observation table:

S. No. Burette reading (ml) Vol. Of iodine


Initial final solution used (ml)
1. .........ml
2. .........ml
3. .........ml
V2=.........ml

Calculation:
1 ml of 0.1 N I2 solution ≡ 0.008805 gm of ascorbic acid

Then,

Ascorbic acid in 0.1 gm ascorbic acid powder = 0.008805 X Burette Reading


=…………………gm.

Result:

Report the percentage purity of given sample of ascorbic acid as final outcome.

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