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Chemical Kinetics: Aim: Principle

The document describes an experiment to study the kinetics of the decomposition of sodium thiosulphate by hydrochloric acid. Sodium thiosulphate solutions of varying concentrations are reacted with an excess of hydrochloric acid, and the time taken for turbidity (precipitation of sulfur) is measured. A graph of the reciprocal reaction times versus concentration is plotted, showing the reaction to be first-order with respect to sodium thiosulphate concentration. The linear graph confirms the decomposition reaction follows first-order kinetics.

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189 views2 pages

Chemical Kinetics: Aim: Principle

The document describes an experiment to study the kinetics of the decomposition of sodium thiosulphate by hydrochloric acid. Sodium thiosulphate solutions of varying concentrations are reacted with an excess of hydrochloric acid, and the time taken for turbidity (precipitation of sulfur) is measured. A graph of the reciprocal reaction times versus concentration is plotted, showing the reaction to be first-order with respect to sodium thiosulphate concentration. The linear graph confirms the decomposition reaction follows first-order kinetics.

Uploaded by

darshan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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CHEMICAL KINETICS

Aim: To study the kinetics of decomposition of sodium thiosulphate by a mineral acid.

Principle:
The decomposition of sodium thiosulphate in hydrochloric acid takes place according to
the following equation:
Na2S2O3 + HCl → 2 NaCl + H2O+ SO2↑+ S↓

The precipitation of sulphur is marked by turbidity in solution and this indicates the
progress of the reaction. The acid is taken in large excess to keep its concentration
more or less constant and solutions of various concentrations of sodium thiosulphate
are used to study the kinetics.

Reagents:
Sodium thiosulphate, N/2 hydrochloric acid

Apparatus:
Measuring cylinder, 5-6 beakers of 250 ml, stop watch, thermometer.

Procedure:
Weigh accurately 0.1, 0.3, 0.5, 0.7, and 0.9 gm of sodium thiosulphate and transfer it to
a 5 beakers. Make their solutions in small amount of water and make each up to 100ml
and label them.
Add 20 ml of N/2 HCl in first beaker and run the stop watch.

Make a big cross mark on a white paper and put beaker on it. View the cross from
above through the solution.

The moment the cross mark becomes invisible, stop the stop watch and note the time
taken.

Repeat the same experiment with remaining four beakers.

Plot the graph, taking amount of sodium thiosulphate per 100 ml of solution on y axis
and reciprocal of time required to bring turbidity on x-axis. It gives a linear pattern.
Observation:
Experimental temperature: …………………………..°C

Observation table:
Amount of sodium Time required for Reciprocal o time
thiosulphate taken Volume of N/2 HCl turbidity ‘t’ 1/t
in gm per 100ml added (in ml)

0.1 20
0.3 20
0.5 20
0.7 20
0.9 20

The data tell that the reaction is of first order with respect to sodium thiosulphate as
reciprocal of time required for turbidity is proportional to initial concentration of
thiosulphate.

Result:
Since the graph is linear (straight line), the decomposition of thiosulphate by mineral
acid is a first order reaction.

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