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Tom Gregan How does changing the concentration of sodium thiosulphate affect the rate of reaction with hydrochloric acid? For my case study I was set the task of how the concentration of sodium thiosulphate affects the rate of reaction with hydrochloric acid. Here is the chemical equation for the reaction, Hydrochloric acid + sodium thiosulphate sodium chloride + water + Sulphur dioxide + Sulphur 2HCL + Na2S2O3 2NaCl + H2O + SO2 + S Hydrochloric acid and sodium thiosulphate are clear liquids but when mixed the solution should go cloudy; when it does we know a chemical reaction has taken place. Carrying out this case study will hopefully help us find out if the rate of reaction is related to the increase in concentration of the reaction. About Collision Theory Collision Theory basically explains how chemical reactions occur and why reaction rates differ for different reactions. This theory is based on the idea that reactant particles must collide for a reaction to occur, but only a certain fraction of the total collisions have the energy to connect effectively and cause the reactants to transform into products. This is because only a portion of the molecules have enough energy and the right orientation at the moment of impact to break any existing bonds and form new ones. ...read more.


We can't control the dependent variable which for example would be the conditions e.g. temperatures of the room we carried out the experiment in this could effect the independent variable in many ways for example it could speed up the rate of reaction or even slow the rate of reaction down we don't know and unfortunately we couldn't control it. The controlled variable in this experiment was the amount of water and sodium thio solution used each time. Sodium Thiosulphate used (cm�) Water Used (cm�) Acid Used (cm�) Experiment 1 Time cross disappeared (s) Experiment 2 Time cross disappeared (s) Experiment 3 Time cross took to disappear) (s) Average Time Cross Disappeared (s) Rate of Reaction 1000/s (s-1) 10 40 5 270.12 277.64 271.14 217.14 3.68 20 30 5 104.04 102.10 103.07 103.07 9.70 30 20 5 69.16 75.35 69.53 69.53 14.38 40 10 5 55.83 56.45 56.14 56.14 17.81 50 0 5 35.01 37.21 36.11 36.11 27.69 Anomalous Results Table of results for main investigation What my reactions did The changing concentration of sodium thiosulphate affects the rate of reaction with the hydrochloric acid; Chemical Equation 2HCL + Na2S2O3 the reaction would reach its end point quicker if it was like this 2HCL + 3Na2S2O3 . ...read more.


I think that there could have been a number of errors made here therefore repeating the experiment for this molarity would be the best idea. My results are first order kinetics because as the molarity of the solution increases, so does the reaction time. My graph also shows that there is a positive correlation and that the results are proportional because as x increases, y also increases. First order reactions mean that as the rate of reaction doubles, so does the concentration. At 0.05M the rate of reaction was 2 S-1, at 0.1M the rate of reaction was 3.6 S-1. This means that as the concentration doubles the rate of reaction almost doubles as well. However, I think that with more experiments and with the improvements I suggested earlier, I think that the rate of reaction would double when the concentration of the solution does. I can also prove this by working out the gradient: m= y/x. The gradient of my graph was 1.3. There is a large increase in the rate of reaction between 10 ml of sodium thiosulphate and 20 ml of it. However, there was only a small increase in the rate of reaction between 30 and 40 ml of sodium thiosulphate. The results could be improved if more experiments were carried out because we could eliminate more anomalous results that occurred which would give very reliable results. ...read more.

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