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Sulphur clock investigation - To see how a change of concentration affects rate of reaction.

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Plan In this investigation, I am changing the concentration of the sodium thiosulphate to see whether it affects the rate of reaction between sodium thiosulphate and hydrochloric acid. The reaction is said to have finished, once the black cross underneath the conical flask has disappeared. The precipitation of sulphur causes the black cross to disappear from view. The equation below shows what will happen when the sodium thiosulphate reacts with the hydrochloric acid in the conical flask. Na2S2O3 + 2HCl S + 2NaCl + SO2 + H2O Theory The theory behind this investigation is the collision theory. If the concentration of the thiosulphate is doubled, this means there are twice as many particles, meaning there are twice as many collisions therefore the reaction time is halved. The diagram below shows the collision theory. = Sodium thiosulphate =hydrochloric acid Variables There are many variables in this investigation and to make sure it is a fair test, many of the variables must be kept the same apart from the independent variable and the dependent variable. The concentration of the sodium thiosulphate is an independent variable and the rate of reaction is the dependent variable. ...read more.


A beaker was filled up with sodium thiosulphate to ensure the same sodium thiosulphate was going to be used, making it a fair test. This was done for the hydrochloric acid also. The sodium thiosulphate, water and hydrochloric acid were measured in to the measuring cylinders. The re-agents were measured to the bottom of the meniscus and made accurate by using a teat pipette. The sodium thiosulphate was added first to the conical flask, the water was added secondly and then finally the hydrochloric acid was added. As soon as all the hydrochloric acid was added from the measuring cylinder, the stopwatch was started. The conical was viewed from the top and once the black cross could not be seen anymore the stopwatch was stopped and the time recorded. The conical flask was washed out using distilled water and the investigation was done again for a different concentration of sodium thiosulphate. The investigation was done twice for each concentration and the average was taken for the two results that were achieved. Results Results One Sodium thiosulphate (cm3) ...read more.


fit in a 5% error margin, where as on the other graph 7 out of 8 points came in contact with the line of best fit in a 10% error margin. This goes to show that experimental error does exist. There was only one anomaly, which was where there was 5cm3 of sodium thiosulphate. If this were done again with a better technique it would come on to the line of best fit. To reduce experimental error, everything should be kept the same. As people were walking in out of the laboratory, the door was being opened and closed so this meant heat was being lost and so therefore the temperature of the room may have fallen causing the reaction to slow down for some concentrations. A burette could have been used to measure out large volumes of liquid instead of using a teat pipette when coming up to the required volume of liquid. If a burette was used, this could have ensured sodium thiosulphate came from the same source. Dilesh Bhardwa 9S Chemistry Investigation - Sulphur Clock Investigation - Page 1 of 7 To see how a change of concentration affects rate of reaction ...read more.

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