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Rates of Reaction

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Rates of Reaction A demonstration was presented to me, showing the reaction between 50ml of sodium thiosulphate solution (concentration 20g sodium thiosulphate/litre of aqueous solution) and 10ml of hydrochloric acid (concentration 37g per litre of aqueous solution) These chemicals, after they have reacted together, produce a product called sulphur. This is insoluble in water and turns the solution cloudy. A cross was drawn on a piece of paper and then placed under the solution, the cross is viewed from above and the time taken for this cross to disappear depends on the amount of time it takes the sulphur to be produced. Dilute Hydrochloric acid reacts with sodium thiosulphate solution to give a precipitate of sulphur. The chemical equation for this reaction is- Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + H2O(I) + SO2(aq) + S(s) It is my task to investigate- "A factor that will alter the rate of the reaction between the sodium thiosulphate solution and hydrochloric acid" "The factor I've chosen that will affect the rate of reaction is the concentration of Sodium Thiosulphate mixed with water and hydrochloric acid." Things that could alter my investigation are ~ Room Temperature ~ Concentration of Sodium Thiosulphate ~ Concentration of Hydrochloric Acid. ...read more.


Each time the experiment was carried (including before the first experiment) out we washed the glass beaker out three times and shook it dry. This was to keep the experiment as fair and accurate as possible and ensure all experiments were carried out under the same conditions. All other variables such as Room Temperature, Stop watch-starting time, Amount of stirring of mixture, etc Were also kept as constant as possible. Experiment We did 6 separate experiments. With 6 different concentrations of Sodium Thiosulphate. Each time the Hydrochloric Acid was kept constant throughout- 10ml. The Sodium Thiosulphate and Water concentration added up to a 50ml solution in total. Sodium Thiosulphate (ml) Water (ml) Acid (ml) 50 0 10 40 10 10 30 20 10 25 25 10 20 30 10 10 40 10 The solution was place on a cross and timed until the mixture became opaque and the cross was no longer visible. These were our RESULTS: - Sodium Thio (ml) Water (ml) Acid (ml) Time 1 (secs) Time 2 (secs) Time 3 (secs) Average Time 50ml 0 10 45 46 42 44 40ml 10 10 53 55 51 53 30ml 20 10 74 71 73 73 25ml 25 10 82 70 74 75 20ml 30 10 98 100 105 101 10ml 40 10 256 200 265 164 I then went on to work out the rate. ...read more.


I would also try to alter the factor of alternating room temperature and would find away of keeping it constants. As different temperature on different day or different times in an hour, quite possible affected the results. I would overcome this problem by either carrying the experiment out in a confined area or a water bath where temperatures were kept constant, this would be known as a thermostatically controlled environment and would be much more accurate. Also I would try to find a more precise and effective way of mixing the solution and timing it from an exact point as this is often varied which unfortunately cannot be helped in the method of our experiment but could be improved. I would also extend the investigation and see how different concentrations of Sodium Thiosulphate effected the experiment i.e. would 40g/l of sodium Thiosulphate react twice as quick with waster and acid as a 20g/l concentration would? However my theory of .I expect "The rate of reaction will be doubled as the concentration is doubled based on the fact that doubling the particles = doubling the amount of successful collisions and then doubling the rate was correct and my experiment was a success. 1 1 ...read more.

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