Effect of concentration on the rate of reaction between sodium thiosulphate and hydrochloric acid

In this article, we have discussed the effect of concentration on the rate of reaction between hydrochloric acid and sodium thiosulphate.

Aim:

The aim of this experiment – Understanding the effect of concentration on the rate of reaction between hydrochloric acid and sodium thiosulphate.

Theory:

The reaction between Sodium thiosulphate (Na2S2O3) and hydrochloric acid (HCl)

To produce a colloidal solution of sulphur, where the solution obtained is translucent.

The reaction occurs as follows:
Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O(l) + SO2 (g) + S(s)

The above reaction when written in its ionic form:
S2O3-2 (aq) + 2H+ (aq) → H2O (l) + SO2 (g) + S(s)

As the temperature of the system increases or as the concentration of reacting species increases the rate of precipitation of sulphur also increases. As the concentration increases, molecular collisions per unit time of the reacting species increase which can result in increased chances of product formation. This results in an increase in the rate of precipitation of sulphur. Similarly, on increasing the temperature, the kinetic energy of the reacting species increases, so the number of collisions that result in the formation of products increase leading to a faster rate of reaction.

Materials required:

The apparatus and materials required for this experiment are as follows:

  1. Flasks 5
  2. Burette of volume 50 mL
  3. Pipette
  4. Burette stand
  5. Stopwatch
  6. Sodium thiosulphate
  7. 1M Hydrochloric acid

Procedure:

The effect of concentration on the rate of reaction:

  1. Take five conical flasks, rinse them with water, and label them 1, 2, 3, 4, 5.
  2. Add 10 mL of sodium thiosulphate solution in flask 1, 20 mL of sodium thiosulphate solution in flask 2, 30 mL of sodium thiosulphate solution in flask 3, 40 mL of sodium thiosulphate solution in flask 4, and 50 mL of sodium thiosulphate solution in flask 5.
  3. Add 40 mL of distilled water in the flask 1, 30 mL of distilled water in the flask 2, 20 mL of distilled water in flask 3, 10 mL of distilled water in flask 4. This is done to adjust the volume of solution in each flask to 50 mL.
  4. Add 1M HCl of volume 10 mL in flask 1 with the help of a burette.
  5. Start the stopwatch immediately.
  6. Take a white tile and draw a cross mark on it.
  7. Add half of the HCl in the flask 1 and shake it well and start the stop-watch.
  8. Observe the flask and start the stop-watch as soon as the cross mark becomes invisible. Record the time taken for the process.
  9. Repeat the experiment by adding 10 mL HCl in flask 2, 3, 4, 5 and record the time for each.

Observation and result

Flask

 

Sodium thiosulphate

 

Distilled water volume

 

HCl volume

 

Time

 

1 10 mL 40 mL 10
2 20 mL 30 mL 10
3 30 mL 20 mL 10
4 40 mL 10 mL 10
5 50 mL 0 mL 10

Precautions to be taken during the experiment:

  • Thoroughly wash the apparatus.
  • The solutions taken for this experiment should be measured accurately.
  • Use the same tile for all the observations.
  • Stay alert while you start and stop the stop-watch.

Viva Voce:

1. What is the amount of sodium thiosulphate added in flask 1?

Ans: 10 mL.

2. What is the amount of distilled water added in flask 1?

Ans: 40 mL.

3. What is the amount of HCl added in all the flasks?

Ans: 10 mL.

4. Name the two solutions used for the experiment.

Ans: Sodium thiosulphate and hydrochloric acid.

5. How many conical flasks are required for this experiment?

Ans: 5.

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