ZIMSEC O Level Combined Science Notes: 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
- Use a measuring cylinder to measure and pour 50cm3 sodium thiosulphate into a clean beaker
- Draw an X on the sheet of paper
- Place the jar over the X on the paper
- Add 5cm3 of dilute Hydrochloric acid to the solution in the jar at the same time take note of the time
- Look down vertically through the solution at the X at the bottom of the jar
- 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
- Rinse the beaker
- Place 40cm3 of sodium thiosulphate into a measuring cylinder and top it up to 50cm3 using distilled water
- Pour into a clean beaker
- Add of 5cm3 acid and note the time it takes for the X to disappear
- Rinse the beaker again
- 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
- Tabulate the results
- 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
- 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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