Keywords: Reaction rates, concentration, temperature, hydrochloric acid, sodium thiosulfate, IGCSE, Prescribed Practical

Introduction: In this practical investigation, we will be exploring how the rate of reaction between hydrochloric acid and sodium thiosulfate is affected by changes in concentration and temperature. The rate of reaction is the speed at which reactants are converted into products, and it can be affected by several factors, including concentration and temperature.

Equipment:

• 50mL hydrochloric acid (0.1M)
• 50mL sodium thiosulfate (0.1M)
• 2 beakers (100mL)
• 2 thermometers
• Stopwatch
• Glass stirring rod
• Marker pen

Method:

1. Label two beakers as “A” and “B”.
2. Measure out 25mL of hydrochloric acid into beaker A.
3. Measure out 25mL of sodium thiosulfate into beaker B.
4. Use the thermometer to record the starting temperature of each beaker.
5. Pour the contents of beaker A into beaker B and immediately start the stopwatch.
6. Use the glass stirring rod to stir the mixture gently.
7. Record the time taken for the reaction mixture to turn cloudy and disappear completely from view. This is known as the “reaction time”.
8. Repeat steps 2-7 two more times for a total of three trials, recording the starting temperature each time.
9. Repeat the entire experiment, but this time use 20mL of hydrochloric acid and 30mL of sodium thiosulfate in beakers A and B, respectively.
10. Repeat the entire experiment again, but this time use 30mL of hydrochloric acid and 20mL of sodium thiosulfate in beakers A and B, respectively.
11. After completing the three trials for each concentration, repeat the entire experiment for each concentration, but this time at a different temperature. Heat the beakers in a water bath to a temperature of 40°C, and record the reaction times as before.
12. Repeat step 11 for a different temperature (e.g. 20°C).
13. Record all data in a table.

Calculations and Expected Findings: Calculate the average reaction time for each set of trials at each concentration and temperature. Plot the data on a graph with concentration and temperature on the x-axis and reaction time on the y-axis. You should expect to see that as the concentration of hydrochloric acid increases or the temperature increases, the reaction time decreases, indicating a faster rate of reaction.

Conclusion: The results of this investigation show that both concentration and temperature have a significant effect on the rate of reaction between hydrochloric acid and sodium thiosulfate. As the concentration of hydrochloric acid increases or the temperature increases, the rate of reaction increases, resulting in a shorter reaction time.

Questions:

1. What is the rate of reaction?
2. What factors can affect the rate of reaction?
3. What is the independent variable in this experiment?
4. What is the dependent variable in this experiment?
5. What is the expected trend for the relationship between concentration and reaction rate?

Answers:

1. The rate of reaction is the speed at which reactants are converted into products.
2. Factors that can affect the rate of reaction include concentration, temperature, surface area, catalysts, and pressure.
3. The independent variable in this experiment is the concentration of hydrochloric acid and the temperature.
4. The dependent variable in this experiment is the reaction time.
5. The expected trend for the relationship between concentration and reaction rate is that as the concentration of hydrochloric acid increases, the rate of reaction will increase, resulting in a shorter reaction time.

• Practical Chemistry