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Investigating the rate of reaction between sodium thiosulphate and hydrochloric acid

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Introduction

Investigating the rate of reaction between sodium thiosulphate and hydrochloric acid Background information In this reaction two aqueous substances, one is sodium thiosulphate and the other is hydrochloric acid are reacted together. to form sulphur, sulphur dioxide, salt and water. Sodium thiosulphate + Hydrochloric acid = Sulphur + sulphur dioxide + Sodium chloride + water Na2 S2 O3 (aq) + 2HCl (aq) = S (S) + SO2 (G) + 2NaCl (aq) + H2O (L) This reaction is no different to any other reaction in that it has several variables in which the reaction can be controlled. In this experiment I will control the rate of the reaction. In order to control the rate of reaction I must only change one variable and keep the others at a constant. This is so I can take fair and accurate measurements. There are several factors which affect how fast a reaction goes. The first is pressure. The more the pressure, the faster the reaction will go, this is because the atoms are pushed closer together so they hit each other more often. This would obviously be too hard to try and control without expensive equipment; also this variable only applies to gases. The next is surface area. The larger the surface area, the faster the reaction. This is because the particles in the solution have more area to work on so there are more reactions resulting in a faster reaction. ...read more.

Middle

Pour the hydrochloric acid into the same flask and at the same time start the stop watch 7. Watch the cross through the flask until you cannot see it anymore and then stop the watch 8. Record the results. Do this 5 times with these concentrations and then repeat them all again. 9. Volume of acid Volume of sodium Volume of water Ratio of sodium to water 8ml 25 0 1 8ml 20 5 0.4 8ml 15 10 0.15 8ml 10 15 0.06 8ml 5 20 0.025 Now I will explain why I have done each step 1. A measuring cylinder is required in order to get the exact amount of each chemical so that the experiment is fair. 2. The cross is placed so that instead of staring through the glass and out the other side there is something to look through at that is going to be the same every test you do 3. Obviously the flask is placed on the cross so you can look down through the liquid onto the cross 6. In order to ensure an accurate measurement you must begin the timer as soon as the mix the chemicals 8. To again insure accurate results I have included a range of five results and repeated them Risk assessment There are several risks when doing this experiment. ? Sodium thiosulphate is an irritant and must be kept away from hands and eyes. ...read more.

Conclusion

Evaluation To make this experiment better I would have used a greater degree of accuracy. Pouring the liquids out by hand creates inaccuracies such as spillage's and other things. Also because I made up my own concentrations they may not have been as accurate as if they had been made up by a machine in a factory so there could have been inaccuracies. Also relying on eye judgement is not a very good way to judge an experiment and also the reception time it takes to stop the stopwatch takes time as well. This adds to the inaccuracy. Having said this, in school laboratory conditions there is not much more that I could have done to make the experiment more accurate without the use of machines. The only thing I could have done would have been to increase my range of results to a large mount so that there was more data and also repeat the results more times to get rid of anomalies and get a good average of results. Safety could not have been better because I was wearing eye protection and the chemicals I was using were in relatively low concentrations. There were no anomalies in this experiment as all of my results fitted in quite well. There are several other ways to do this experiment also. I could have measured the amount of gas being given off in one minute and then derived a rate of reaction from that. ...read more.

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