ABHINAY RAWAT
To Study the Reaction Rate of the
Reaction between Potassium Iodate
(KIO3) & Sodium Sulphite (Na 2S03)
Using Starch Solution as Indicator
Objective
To study the reaction between potassium iodate
(KIO₃) and sodium sulphate (Na₂SO₄) using starch
solution as an indicator.
Theory
The rate of a chemical reaction may depend on the
concentration of one or more reactants or it may be
independent of the concentration of a given reactant. The
rate dependance on the reactant concentration is
expressed in an equation called the Rate Law.
For a general reaction of the type, xA + yB C, the rate
law can be written as,
Where, K is the rate constant, [A] and [B] are the
concentration of the reactants, x and y are the exponents
that define how the rate depends on the concentration of
individual reactants. The exponents x and y are also
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referred to as the order of the reaction with respect to a
particular reactant. The reaction order for each reactant in
the rate law determines how the rate changes as the
concentration of the reactant changes. If the order of a
reactant is zero, the rate is independent of its
concentration.
Reaction between Potassium Iodate and Sodium Sulphite
The effect of concentration of the reactant on the rate of a
chemical reaction can be studied by analysing the
reaction between potassium iodate and sodium sulphite.
In acidic medium, potassium iodate is reduced to iodide
by sodium sulphite. The reaction takes place through the
following steps.
Step I: Sulphite ions react with potassium iodate
producing iodide ions.
Step II: Iodide ions formed are oxidized to iodine by
reaction with more iodate ions.
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Step III: Iodine formed in Step II reacts immediately
with sulphite ions forming iodide ions.
When sulphite ions are completely consumed, the
liberated iodine would react with starch solution, to give
a blue colour. So this reaction can be monitored by
adding a known but limited volume of sodium sulphite
solution and starch solution. This is an example of Iodine
Clock Reaction, as the rate of reaction is estimated by the
time taken for the appearance of blue colour. The faster
the reaction, the shorter the time required for the blue
colour to appear. Adding dilute solution of potassium
iodate, decreases the concentration that decreases the rate
of reaction. Conversely increasing the concentration of
the reactant increases the rate of reaction.
The following graphs show that the rate of the reaction is
directly depends on the concentration of potassium
iodate.
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ABHINAY RAWAT
Materials Required
Potassium iodate (KIO₃) solution, Sodium sulphate
(Na₂SO₄) solution, Starch solution (indicator),
Beakers, Pipettes, Measuring cylinders, Distilled
water, Test tubes, Glass rod
Procedure
1. Take 50 mL of potassium iodate (KIO₃) solution in a
clean beaker.
2. Add 50 mL of sodium sulphate (Na₂SO₄) solution to
the same beaker.
3. Stir the mixture thoroughly using a glass rod.
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ABHINAY RAWAT
4. Add a few drops of starch solution to the reaction
mixture.
5. Observe the color change in the solution.
6. Record the observations and note the formation of
any precipitate or change in color.
Observations
Record the following observations:
FLAS 0.1 M 2M Wat Starch 0.01M Time for
K KIO3 H2S er Soluti Na2SO appeara
Soluti O4 (ml) on 3 nce of
on (ml) (ml) Soluti blue
(ml) on colour
(ml)
A 10 10 80 5 25
B 20 10 70 5 25
C 30 10 60 5 25
D 40 10 50 5 25
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ABHINAY RAWAT
1. Initial color of the mixture before adding starch
solution.
2. Color change after adding starch solution.
3. Formation of any precipitate.
Result
The reaction between potassium iodate (KIO₃) and
sodium sulphate (Na₂SO₄) in the presence of starch
indicator results in a distinct color change, indicating
the progress of the reaction.
Precautions
1. Use freshly prepared starch solution for accurate
results.
2. Handle all chemicals with care and wear
appropriate safety gear.
3. Ensure that all glassware is clean before use.
4. Measure the solutions accurately to maintain
consistency.
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ABHINAY RAWAT
Detailed Procedure
1. Prepare a 0.1 M solution of potassium iodate (KIO₃)
by dissolving the required amount of KIO₃ in distilled
water.
2. Similarly, prepare a 0.1 M solution of sodium
sulphate (Na₂SO₄).
3. Using a pipette, measure 25 mL of KIO₃ solution
and transfer it to a clean beaker.
4. Add 25 mL of Na₂SO₄ solution to the beaker
containing KIO₃ solution.
5. Using a dropper, add 5 drops of starch indicator to
the mixture.
6. Stir the solution gently using a glass rod and
observe the changes.
7. Note the time taken for the color change to occur
after adding the starch indicator.
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ABHINAY RAWAT
Diagrams
Molecular structure of potassium iodate (KIO₃).
Expanded Observations
Observations for this experiment are as follows:
1. The initial color of the mixture is colorless or
slightly yellow.
2. After adding the starch indicator, the solution
gradually turns blue, indicating the formation of
iodine.
3. The intensity of the blue color depends on the
concentration of iodine in the solution.
4. No precipitate formation is observed during the
reaction.
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ABHINAY RAWAT
Conclusion
The reaction between potassium iodate and sodium
sulphate demonstrates the role of redox processes in
chemical reactions. The use of starch as an indicator
provides a clear visual cue for the presence of iodine,
which helps in understanding the underlying
chemistry.
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