Experiment: Determining how concentration affects rates of reaction

Aim: To find the effects of concentration on the rate of reaction using hydrochloric acid and sodium thiosulphate

Materials: 250cm³ beaker, measuring cylinder, stop clock/a watch/phone with a stop watch app, sheet of white paper, dilute hydrochloric acid, sodium thiosulphate

Method

1. Use a measuring cylinder to measure and pour 50cm³  sodium thiosulphate into a clean beaker
2. Draw an X on the sheet of paper
3. Place the jar over the X on the paper
4. Add 5cm³  of dilute Hydrochloric acid to the solution in the jar at the same time take note of the time
5. Look down vertically through the solution at the X at the bottom of the jar
6. Note the time it takes for the X to “disappear” i.e the solution becomes so cloudy it is impossible to view the X through the solution
7. Rinse the beaker
8. Place 40cm³  of sodium thiosulphate into a measuring cylinder and top it up to 50cm³  using distilled water
9. Pour into a clean beaker
10. Add of 5cm³  acid  and note the time it takes for the X to disappear
11. Rinse the beaker again
12. Repeat the test using 30cm³ , 20cm³  , and 10cm³  topping up to 50cm³  with water each time. Take note of the time it takes for the X to disappear
13. Tabulate the results
14. Plot the results on a graph with the amount of sodium thiosulphate on the y-axis and time it takes for the X to dissappear on the x-axis

Results and observations

Rate of reaction and concentration. Image credit bbc.com

• Diluting the sodium thiosulphate decrease its concentration
• Each time the concentration is reduced the X takes longer to disappear

Conclusion

• The higher the concentration of a solution the faster the rate of the reaction
• All things being equal increasing the concentration of  one or more of the reagents results in an increase to the rate of reaction

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