Describe an experiment to show that the rate of a reaction depends on the concentration of the react(s).

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The reaction between sodium thiosulphate and hydrochloric acid can take a noticeable time.
Sulphur is produced during the reaction making the solution cloudy. The rate of reaction can
be found by finding the time taken to reach a certain degree of cloudiness in the solution.
The degree of cloudiness in this case may be defined as the point at which a black cross
marked below the reaction vessel can no longer be seen by looking through the solution from
above. In this experiment the concentration of sodium thiosulphate is made variable, whilst
the concentration of acid is kept constant. Sodium thiosulphate may be bought as "hypo"
which is used in photography. Make up 500 mL of aqueous solution containing 20 g sodium
thiosulphate. 2 M hydrochloric acid is also needed. Bench dilute acid is usually of this
strength. Using a measuring cylinder, put 50 mL of thiosulphate solution into a 100 mL
beaker. Place the beaker on a black cross marked on a sheet of paper. Add 5 mL of the acid
and note the time given by the second hand of a clock. Stir the acid into the solution. Note
the time when the cross is no longer visible through the sulphur in the solution. Repeat the
experiment with a smaller concentration of thiosulphate. Take 40 mL of thiosulphate
solution and add 10 mL of distilled water. Stir and then add 5 mL of acid as before. The
time for the cross to become invisible should be greater than for the last experiment.
Repeat the experiment using 30 mL, 20 mL and 10 mL of this sulphate mixed with 20 mL, 30
mL and 40 mL of distilled water. Plot concentration of the thiosulphate solution against time
taken for the reaction. Concentration values may be taken as the volume of the original
thiosulphate solution used. Since I/time, reciprocal of time, is the measure of the rate of
the reaction, plot thiosulphate concentrations against I/time. The equation for the reaction
can be written as:
Na₂S₂O₃ (aq) + 2HCl(aq) --> H₂O (l) + SO₂ (g) + S(s)

sharon kalunda answered the question on April 12, 2019 at 09:16

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Describe an experiment to show that the rate of a reaction depends on the concentration of the react(s).

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