Some of the factors that will affect my investigation are temperature of Sodium Thiosulphate, temperature of Hydrochloric Acid, concentration of Sodium Thiosulphate, concentration of Hydrochloric Acid, volume of Sodium Thiosulphate and volume of Hydrochloric Acid.
Temperature of Sodium Thiosulphate – this will affect my experiment by giving the Sodium Thiosulphate particles more kinetic energy, meaning they will move faster, resulting in a higher number of successful collisions. I will control this by putting my Sodium Thiosulphate solution in a water bath that is at 40°C.
Temperature of Hydrochloric Acid – this will affect my experiment by giving the Hydrochloric Acid particles more kinetic energy, meaning they will move faster, resulting in a higher number of successful collisions. I will control this by putting my Hydrochloric Acid solution in a water bath that is at 40°C. Combining this with Sodium Thiosulphate also at 40°C will ensure a fair test.
Concentration of Sodium Thiosulphate – this will affect my experiment by giving the Hydrochloric Acid particles more Sodium Thiosulphate to react with meaning they will have more successful collisions. I will control this by not changing it so that it remains at 40g/m3.
Concentration of Hydrochloric Acid – As concentration of the Hydrochloric Acid gets higher the rate of reaction will be lower, this is because if the solution is more concentrated it means there are more particles of Hydrochloric Acid in between the water molecules, which makes collisions between important particles more likely. I will control this by changing it every time.
Volume of Sodium Thiosulphate – this will affect my experiment by giving the Hydrochloric Acid particles physically more Sodium Thiosulphate to react with meaning they will have more successful collisions. I will control this by not changing it so that it remains at 20 cm3.
Volume of Hydrochloric Acid – this will affect my experiment by giving the Sodium Thiosulphate particles physically more Hydrochloric Acid to react with meaning they will have more successful collisions. I will control this by not changing it so that it remains at 20 cm3.
I will use these measurements because it will provide a suitable range and number of results. I will use such high volumes because it will make it easier to get a more accurate time for the reaction, resulting in a more accurate graph.
I will use the following equipment: -
- Paper – to draw the cross on.
- Ink – to draw the cross with.
- Stopwatch – to time the experiment.
- Conical Flask – to contain the reactants.
- Measuring Cylinder – to measure out the reactants.
I have done a pre-test, the results were: -
I used 2 ml of Hydrochloric Acid, 2ml of Sodium Thiosulphate. From this experiment I conclude that the experiment will not take very long and I will use higher volumes of both solutions.
RESULTS
CONCLUSION
I have found out that as concentration of the Hydrochloric Acid gets higher the rate of reaction gets lower, this is because if the solution is more concentrated it means there are more particles of reactant in between the water molecules, which makes collisions between important particles more likely. The results support my prediction by showing this. It compares with my predicted graph exactly.
EVALUATION
I think that the procedure used was not very scientific as it didn’t produce quantitive results, e.g. 5g of gas was produced. I had one anomalous result, I cannot explain this with a certain reason but I think it may have been on my part and I may not have measured my quantities properly.
My investigation was a fair test because I: -
- Used the same conical flask as any other ones may be contaminated or cleaner.
- Used the same measuring cylinder, but a different one for each substance as any other ones may be contaminated or cleaner.
- Used the same volume of Sodium Thiosulphate every time as more will make it a different experiment.
- Repeated the experiment three times to avoid any anomalous results, although I did get one.
- Used the same cross as a different cross on different paper would fade at a different rate.
I could have made it a fairer by: -
- Completing the experiment in one session as I could have guaranteed using the same substrates.
The difficulties I faced were judging when the cross had faded, measuring out the exact quantities as I used such exact volumes and making sure I didn’t get confused between all three solutions as they were all clear. If I were to repeat the experiment I would use less exact measurements label each solution, this would be to avoid cross contamination of my solutions therefore making my experiment invalid. To obtain more evidence of my solution I would use more accurate measuring equipment and do more molarities of Hydrochloric Acid.
