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Investigating how the concentration ofthiosulphate solution affects the rate of reaction.

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Introduction

Investigating how the concentration of thiosulphate solution affects the rate of reaction. Aim: My aim is to investigate how different concentrations of sodium thiosulphate solution affect the rate of reaction. Hypothesis: As you increase the concentration (molarity), the rate of reaction will increase. I think this because a high concentration means a large number of particles in a given volume. If there are more particles and the activation energy is right, then there will be more collisions. More collisions mean a large number of successful collisions. Therefore the rate of reaction will increase. Introduction: In this investigation I am going to carry out an experiment to determine the effects of different concentrations of thiosulphate solution on the rate of reaction. I will do this experiment using the following formula: Na2S2O3 + 2HCl 2NaCl (aq) + H2O + SO3 + S(s) I will only change the concentration of the sodium thiosulphate solution to see if this effects the reaction i.e. if it speeds it up. I will use 50cm3 of thiosulphate solution. I will have to do some calculations to be able to work out an appropriate volume of hydrochloric acid (HCl) Scientific knowledge: With high concentrations the rate of reaction will be fast. This is because according to the collision theory the more you increase the concentration of a substance then the rate of collision increases. ...read more.

Middle

I have shown the working out that I have used to obtain the results in the above table on the previous page. * You measure 13cm3 of hydrochloric acid using a measuring cylinder and then put it into the conical flask. (I have rounded 12.5cm3 to 13cm3 so that it will be easier for me to measure it more accurately.) * You then draw a cross onto the paper and place the conical flask directly onto it. * Then you make your first dilution using a measuring cylinder * When you have done this, you quickly add it into the hydrochloric acid (conical flask) timing it as soon as you put it in. * You then start swirling the conical flask to allow the solution to mix keeping your eyes over the flask. * As soon as you are unable to see the cross any more, stop your stop clock. * Record your first result in a results table. * You use the same procedure for each of the different concentrations making sure that you wash the equipments before reusing them so that no errors can occur. Results: Volume Conc of thio Concentration 2M volume Time cross disappears Average time cross disappears Rate of Reaction cm3 M M /cm3 Min: sec sec 1/sec 50 0.250 2 13 00:30 00:28 00:27 00:28 3.57 45 0.220 2 13 00:32 00:31 00:31 00:31 3.23 ...read more.

Conclusion

the same person will add the thiosulphate into the acid for each trial and the same person will judge when the precipitate is formed. This can cause an error if different people carry out the same procedure as everyone has different judgments and different eyesight's. A better improvement for watching when the precipitate is formed is to use a light meter to obtain the timing of the reaction instead of using human eyesight. As I was carrying out the experiment I had found that I did not use the same pen. This can be improved by using the same pen to make sure that the same darkness of a pen is used. Extension Further work that could be carried out is that instead of using hydrochloric acid I could use different acids e.g. Nitric acid or sulphuric acid. To see its effects I could use a high concentration of sodium thiosulphate and hydrochloric acid. I could also use a lower concentration for the acid, if I was to use the same equation, or I could increase the range of the concentrations that I used. I could also use different concentrations of hydrochloric acid and keep sodium thiosulphate constant to see how this effects the reaction, if any. Other extensions could include measuring the rate of reaction not by using the precipitation method but the change in mass method or by measuring the volume of gas given off. ...read more.

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