sodium thiosulphate reacting with hydrochloric acid

Hydrochloric acid

Paper and pen

Stopwatch

Measuring flasks

I predict that as the concentration of the sodium thiosulphate decreases that the time for the reaction to take place will increase.

Procedure

1. Collect equipment
2. Set up equipment
3. Measure out solutions of sodium thiosulphate
4. Add hydrochloric acid
5. Place on paper on top of cross
6. Start stop watch
7. Observe
8. Stop the stop watch once cross is no longer visible
9. Note results in table        
10. Repeat for other solutions and copy all results in a table

Pre work

I ran a pre work experiment and these were the results

This pre work proved my theory and therefore made my experiment worthy. As these results show an increase in time occurred when the solution was watered down.

Chemical equations

Sodium thiosulphate + hydrochloric acid

       Na2S2O3 (aq)    + 2HCl(aq)

This gives

Sulphur + sodium chloride + sulphur dioxide + water

  S (s)            2NaCl(aq)              SO2(g)             H2O

Sulphur appears in the form of very small particles of solid. The particles remain in suspension. The picture shows how we studied the speed of the reaction. During the experiment we only changed the sodium thiosulphate and the water content and kept the hydrochloric acid content the same. As we were dealing with acid goggles were worn at all times.

1. Acid and sodium thiosulphate solution are reacting to form sulphur
2. You are timing how long it takes to form enough sulphur to block your view of the cross
3. You do this with different concentrations of sodium thiosulphate

Results table and graph

As this graph shows there is an obvious increase in time as the solution is weakened. This is because as the water is added there as less particles of ST for the hydrochloric acid to collide with there fore not causing such a violent reaction.