The amount of water could slow down the reaction because it could make the concentration of the acid weaker and therefore it will take longer to react with the sodium thiosulphate.
The concentration could easily alter the rate of reaction because if the acid is very weak than it would take a very long time to react with the sodium thiosulphate.
The pH of the water could alter the rate of reaction because the properties in the water could contaminate the rest of the liquids.
The boldness of the cross, which is under the conical flask, could affect the results because it is easier to see a bold cross in the smoke than it is to see a thin cross in the smoke.
Equipment
- Sodium Thiosulphate
- Hydrochloric acid
- Water
- Paper with a cross on it
- 2 measuring cylinders
- 1 conical flask
Method
- Put the conical flask over the cross
- Add the desired amount of water into the conical flask
- Prepare the correct measurements of hydrochloric acid and sodium thiosulphate in the two measuring cylinders
- Pour both of them into the conical flask at the same time and start the stopwatch
- Stop the stopwatch when you can no longer see the cross whilst looking down into the conical flask.
- Do all of the 5 tests this way than repeat all five tests in a second experiment.
I will repeat this experiment twice and then work out an average of both tests. This should make the results as accurate as possible and not create any anomalous results.
I will make it a fair test by making sure I keep to the stated volumes of each substance and that I do not change any of them. I will also wear safety goggles to make sure that I do not get any of the substances in my eyes.
Prediction
I predict that the less sodium thiosulphate you use in the experiment the slower the reaction will be and vice versa. I believe this because I found out that the volume of a substance can greatly affect the rate of reaction and usually the more of the substance you use the quicker the rate of reaction will be.
Preliminary Experiment
I did the experiment first to test the extreme values (the highest and lowest volume of the sodium thiosulphate). I found out that the volumes were suitable for the experiment because the highest value only had a rate of reaction of about 2 minutes 20 seconds, which is about long enough for each test.
I also did a test on how temperature affected the same reaction. I found out that the higher the temperature the faster the reaction was.
Results
A table to show the rate of reaction
Conclusion
My graph shows that there is a curve in the rate of reaction. This means that as you add more sodium thiosulphate the rate of reaction increases very quickly. All three of the lines are curves which make my results fairly accurate and the average line goes right in the middle of the two tests. The average line is most likely to be the most accurate. There are no anomalous results in my graph. I think that this is because I planned my experiments out very well and made sure that I could not make any errors. My results mean that the higher the volume of the sodium thiosulphate the faster the rate of reaction will be. My prediction was correct and the results back up my first ideas that there is no constant line (straight line) increasing, it is a curve.
Evaluation
My method of finding out by results was by recording how long it took me to not be able to see a black cross through the solution. My results were very accurate and I think that this was because I made sure that nothing could go wrong and the preliminary tests made sure that I would not make the extreme variables too high or too low. I think that if I repeated the experiment three times it would make the results far more accurate, but it may create some anomalous results. My results are still very reliable even though I only repeated them once. I think that I would have to research a lot more variables and do a lot more experiments to get enough evidence to back up my conclusion. To improve my results I could use far more accurate measuring cylinders and repeat the experiment a lot more times. I think that if the experiment was repeated than there would be a 75% chance that I would get the same results. This is because a lot of my results from the two experiments are very similar or even the same. I could easily find out what other factors affect the rate of reaction. If I could do one of them I would do a full experiment on how the temperature would affect the rate of reaction. To do this I would need to use heating equipment and heat the five conical flasks, with the exact same volumes of the solution in, to five different temperatures and find out which one was the longest and which on ewas the shortest. This could help me find out how to make my experiment more accurate because if the room temperature changed than it could have affected my results.
