Rate of reaction: sodium thiosulphate and acid

A/L Chemistry · G.C.E. Advanced Level · Grades 12–13

Aim

To investigate how temperature affects the rate of reaction between sodium thiosulphate and hydrochloric acid.

Apparatus

• Sodium thiosulphate solution and dilute HCl
• Beaker over paper with a cross, thermometer
• Stopwatch and water bath

Method

1. Warm the thiosulphate solution to temperature T.
2. Add the acid and start the stopwatch.
3. Look down at the cross and stop when it disappears.
4. Record the time t; rate ∝ 1/t.
5. Repeat for 5 temperatures.

Conclusion

As temperature rises, t falls and 1/t (the rate) rises rapidly: roughly doubling for every 10 °C.