Concentration of hydrochloric acid – the concentration of hydrochloric acid must also stay the same to prevent the rate of reaction changing and thus and unfair test.
Step by Step Plan of Investigation
In my investigation on rate of reaction, to start I collected 3 glass beakers and filled one with sodium thiosulphate, one with hydrochloric acid and the last with water. To start with before my investigation began, I did a series of pre-tests to help determine what colour my cross should me, how bold it should be, and how large it should be. We tested a combination of bold, thin, yellow and red crosses till we finally determined that a bold red cross would give the better results. Now, I was ready to begin my investigation into how the rate of reaction is affected by factors such as the concentrations and heat. To begin with I took my syringe and put 50 cm3 of sodium thiosulphate in to a conical flask after accurately and safely measuring it with my syringe. Then I accurately measured out 5 cm3 of hydrochloric acid and added it to my sodium thiosulphate, this is when the reaction started so is started my stop clock. Once the cross disappeared due to sulphur forming in the solution I stopped my stop clock and wrote down the time taken to hide the cross. I repeated this 3 times. After that I put 45 cm3 of sodium thiosulphate into a clean conical flask but this time I added 5 cm3 of water and 5 cm3 of hydrochloric acid to it at the same time, then once again started my stop clock. To ensure the test was as fair as possible, I once again repeated it 3 times. I then repeated each the same for the other 3 rows in my table below. Once this was complete and I was convinced it had been as fair as possible I then washed by equipment and put it all pack in the correct place and washed my hands to be sure there was no solution on them.
Range of Concentrations
Conclusion of my Investigation on the Rate of Reaction and its Affecting Factors
I have completed my investigation and have investigated fully what affects the rate of reaction. My graphs on the rate of reaction compared to the concentration and the time taken to hide the cross fully compared to the concentration show that what I predicted was correct. As shown on the first page of my coursework, I wrote that “I predict, due to my own knowledge on the variables that affect the rate of reaction, that if the experiment takes place fairly and accurately, the higher the concentration of sodium thiosulphate in a solution with water and hydrochloric acid, the higher the rate of reaction for this experiment will be. Plus, the more concentrated the solution, the less time it will take for the cross to become fully hidden by the formed sulphur”. I know that my prediction was indeed correct as when the concentration was at 6 grams per litre, my graph shows the rate of reaction was at 0.11 per second, but when the concentration had increased to 9 grams per litre, my graph shows the rate of reaction being 0.45, showing an increase in the rate of reaction as the concentration is increased. However, there was one anomaly shown one each graph I drew out. Further research ahs led me to believe that these were causes by a number of factors. One such being that the sunlight was shining directly onto my solution which warmed it up and increased the rate of reaction. But then for a certain period of time, it was hidden by cloud cover. Another possible problem I encountered which could cause an anomaly on my graph is that my team mate who was watching the cross was not present for one part of the experiment, meaning I had to watch it instead. This meant that because I have different eye sight to him, I saw the cross disappear earlier than he potentially would of. The reason the cross disappears is all to do with the collision theory. The collision theory is basically the idea that more collisions happen between particles in a more concentrated solution than it would do in a lesser concentrated solution. I believe from my observations that the higher the concentration of sodium thiosulphate against water and hydrochloric acid means that more collisions take place in the solution between sulphur particles. This then means that the solution becomes more opaque due to the frequency of collisions.
In order to improve my test results if I was to do it again, I and my team mate would have to keep the test fair by keeping the same person watching the cross. Also to improve my experiment results I would conduct my experiment in an area of the classroom were it could not be affected by heat radiation from the sunlight, such as a corner of the classroom were sunlight is blocked by a bookcase or filing cabinet. One further way that I could improve my experiment would be by using a colorimeter rather than eyes to detect when the cross is completely covered by the formed sulphur. A colorimeter is a device that measures the amount of light that travels through something. By using one of these it would improve the accuracy of the test by telling us when no light gets through to the cross on the paper below the conical flask. When no light is detected, that is when the cross is fully hidden by sulphur. Apart from those I would keep everything in my test the same as I have written and would still exercise the same amount of safety I used during this experiment, such as wearing safety glasses again and washing hands as soon as possible after the experiment to ensure no hydrochloric acid or sodium thiosulphate I left on or it could result in injuries such as acid burns.
