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Reaction between thiosulphate and hydrochloric acid

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Introduction

An Investigation Into The Rate Of The Reaction Between Dilute Hydrochloric Acid And Sodium Thiosulphate Plan Aim The aim of this investigation is to investigate the effect of changes in concentration of the sodium thiosulphate on the rate of the reaction between dilute hydrochloric acid and sodium thiosulphate. Variables There are four main variables that affect experiments such as this. They are: * The Temperature Of The Reaction Reactions get faster as the temperature is increased. As a rough approximation, a 10�C increase in temperature doubles the rate of a reaction. There are two factors at work here. 1) Increasing the temperature means that the particles are moving faster and so collide with each other more often. That will make the reaction go faster, but it only accounts for a small part of the increase in rate. 2) Not all collisions end up in a reaction. Many particles just bounce of each other. In order for anything interesting to happen, the particles have to collide to create a minimum amount of energy called Activation Energy. A relatively small increase in temperature produces a very large increase in the number of collisions which have enough energy for a reaction to occur. ...read more.

Middle

Procedure When dilute hydrochloric acid and sodium thiosulphate are mixed, a yellow precipitate of sulphur gradually appears. A cross will be drawn on a piece of paper in pen. This cross will be placed under a conical flask, in which the sodium thiosulphate and dilute hydrochloric acid will be mixed. In one of the measuring cylinders a certain amount of sodium thiosulphate will be measured together with a certain amount of water, to dilute the solution. In the other a constant amount of dilute hydrochloric acid. Both will then be mixed into the conical flask and timed. The stopwatch will be stopped when the precipitate formed completely covers the cross so that it has disappeared from view. The time will then be recorded and the experiment repeated with different concentrations of sodium thiosulphate. The results will then be presented in a table such as this: HCL (cm�) Thiosulphate (cm�) Water (cm�) Time 1 (sec.) Time 2 (sec.) This data will then be presented as a graph. A minimum of five different results will be taken each repeated at least twice. This will ensure the accuracy of the results. To keep it a fair test the experiment will be carried out in the same place, so the temperature will remain on average about the same. ...read more.

Conclusion

The more dilute the solution the less sodium thiosulphate particles present. This will then mean the chance of a favourable collision between a sodium thiosulphate particle and a dilute hydrochloric acid particle will be reduced. Hence the time taken for all the particles to have collided with each other will be reduced. This is the scientific reasoning behind the results obtained. Evaluation Overall I believe the investigation went quite well and the procedure was an accurate and an appropriate way to carry out such an investigation. Even though there were no anomalous readings the test was not completely accurate. The procedure was very susceptible to human error. The stopwatch could be stopped late or the cross could be seen by one person but have disappeared to another. The investigation was however fair and quite reliable, as the instruments were cleaned out properly and the same conditions were used for all the experiments. One obvious improvement is the variable of temperature; it was neither checked nor controlled in any way. Controlling the temperature would allow for the investigation to be truly fair but due to practical limitations this was not possible so it, in this case, is appropriate to assume it as room temperature and as not changing much. Overall I think the test went well, tangible results were obtained, the prediction proved and, surprisingly for an investigation like this, no anomalous readings were formed. ...read more.

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