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Find out what the rate of reaction is for sodium thiosulphate in hydrochloric acid.

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Year 10 Chemistry Coursework Aim In this experiment I will find out what the rate of reaction is for sodium thiosulphate in hydrochloric acid. The Collision Theory When two particles collide and exchange or transfer energy. The speed at which they collide and whether they collide the right way round (orientation of the collision) effects the reaction and the speed of the reaction. This diagram shows the collision theory. It shows the need for the particles to collide with the correct orientation as in collision 1 on the diagram. Planning In this experiment I will add different concentrations of sodium thiosulphate of the amount 5ml to 5ml of hydrochloric acid and time the time it takes for the mixture to be opaque enough that it cannot be seen through. To test this the mixture will be in a glass beaker, which is on top of a small piece of laminated cardboard with a bold cross on it. I will start the timer as soon as I add the sodium thiosulphate to the hydrochloric acid and stop the timer as soon as I can no longer see the cross underneath the beaker. I will have hydrochloric acid as the constant variable and the concentration of sodium thiosulphate as the varied variable. ...read more.


* Keeping the beakers, measuring cylinders and conical flask clean between experiments. Variables Constant variables: * Temperature * Volume of hydrochloric acid (10ml) * Concentration of hydrochloric acid * Source of the water * Person doing timing The only variable that I will change is the concentration of sodium thiosulphate. Chemical Reaction Hydrochloric acid + Sodium Thiosulphate + Water = Sulphur dioxide + sulphur + water 2HCL(aq) + NA2S2O3 (aq) + H2O (aq) = 2NACL (aq) + H2O (aq) + SO2 (aq) + S (s) Sulphur is the substance which causes the cloudiness that obscures the cross. Method I firstly measured 10ml of hydrochloric acid using a small measuring cylinder and then added it to an empty conical flask. I then measured out the 10/9/8/7/6/5ml of sodium thiosulphate and the 1/2/3/4/5ml of water in 2 separate measuring cylinders. I then added them at the same time to the hydrochloric acid and started the timer. I stopped the timer at the point at which I could not make out that the shape was a cross, which is where I could not see it at all. I did the same 3 times for each different amount of sodium thiosulphate. To make the experiment a fair test I did not mix the sodium thiosulphate and water until they were both added to the hydrochloric acid. ...read more.


The rate graph also shows that the reaction is fastest when there is the most sodium thiosulphate. In the rate graph an anomaly is also clear where there is 8ml sodium thiosulphate and 2ml water. The graphs show what I explained in my prediction was correct. Evaluation My experiment went well. I got the results to all of the readings I wanted and I got enough information to produce good accurate tables and graphs. There weren't many anomalies in my results except for in the rate graph there is a clear anomaly for 8ml of sodium thiosulphate and 2ml water. This anomaly may have occurred because of a couple of different reasons. I obtained my results on a number of different days so the temperature may have differed and therefore affected the reaction. There is also the possibility that after washing the conical flask, beakers and measuring cylinders between experiments that there was drops of water left in them. This water may have affected the experiment as it would dilute the mixture further and therefore slow it down due to the collision theory, which I have explained. If I were to do the experiment again I would try to obtain all of my results on the same day so that the temperature would be the same. I would also dry out the equipment after washing it between experiments so that there would be no water left. ...read more.

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