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Effect of concentration on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid

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Effect of concentration on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid Aim: The aim of the experiment is to find out if the concentration of Hydrochloric acid effects the rate of reaction between sodium thiosulphate and hydrochloric acid. Equation: Na2 S2 O3(aq) + 2HCL(aq) H2O(1) + SO2(g) + S(s) + 2NaCL(aq) Sodium thiosulphate + Hydrochloric acid Water + Sulphur dioxide + Sulphur + Sodium Chloride Preliminary work: The main aim of this experiment is to find out about concentration. This means that I will require having knowledge on the subject. Concentration is the number of molecules of a certain substance in a solution with other substance. An easy way of explaining this is with Ribena drink. When you first pour the ribena into a glass the ribena is 100% concentrated. After that you then add water, the water dilutes the ribena and alters the concentration of it. This means that the drink has been diluted and is not so concentrated. The diagram below illustrates this (diagram 1). Diagram 1: Each of the circles represents a molecule of either ribena or water, purple for ribena and blue for water. When the two are mixed together you are left with a solution. The solution is made up of a number of both molecules. This is very similar to the reaction between sodium thiosulphate and hydrochloric acid, which produces a solution. ...read more.


This is to ensure that the chemicals are not spilt or splashed, this would be a health hazard and also effect the volume of the reactants. Once the two reactants have been combined I will ask for my helper to begin the timer, this will be when the second beaker is empty. I will then proceed to stir the reactants using a glass rod, it will be moved in the same motion and speed as not to differ between tests. This will affect the rate of reaction, as it would increase the likelihood of particles bonding, this is explained in the preliminary work. As the reaction proceeds the cross on the paper should begin to disappear. I will monitor the visibility from the same angle for all reactions and with the same intensity and direction of light. This is to ensure that the cross disappears from sight at the same moment in each test. A change in the view of the reaction could result in the obstruction or refraction of the cross. For this reason also one beaker is used so that the thickness of the glass does not affect the view of the cross. Once the cross is no longer visible I will then ask for the timer to be stopped, however the reaction will still be continuing to take place. However this is not relevant to this experiment. ...read more.


To improve the experiment I would have liked to control new factors that affect the rate of reaction between sodium thiosulphate and hydrochloric acid, for example I could try changing the temperature of the reactants or introduce a catalyst. The effect of these factors on the reaction rate is explained earlier in the preliminary work. Also I could refine the method to allow more tests and a wider range of results to back up my findings. There could also be more experiments carried out by different people who could then combine their result with mine to check them. I did attempt to control the temperature of the environment in which the reaction was taking place, as there are not the facilities at school to keep the temperature at a constant one for all experiments. There was also another factor that could have affected our results. This is that I took hydrochloric acid from two different batches, which was necessary for safety purposes. This means that it was possible that one batch was of a higher concentration than the other was, this would result in the concentration of hydrochloric acid being fractionally different from those stated in the results. To prevent this I would like to use undiluted acid in a new experiment. Also it would be possible to investigate the effect of concentration on other reactions. I would also continue to ensure that the test is carried out in the safest and fairest possible manner. Craig Banfield - 1 - ...read more.

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