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Investigating the rate of chemical reaction between sodium thiosulphate solution and dilute hydrochloric acid

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Introduction

Investigating the rate of chemical reaction between sodium thiosulphate solution and dilute hydrochloric acid Plan: I am going to investigate how varying the concentration of Sodium Thiosulphate affects the rate of reaction with Hydrochloric Acid up until a fixed point. The equation for the reaction is: Sodium Thiosulphate + Hydrochloric Acid �> Sodium Chloride + Water + Sulphur + Sulphur dioxide Or: Na S O + 2HCl �> S + 2NaCl + H O + SO This reaction has a set end point (when the cross on the test tube 'disappears'). The faster the cross 'disappears' the faster the reaction and by timing how long this takes we can establish the rate of reaction. There are various factors affecting the rate of reaction that we need to take into consideration, these are: > Temperature - I will conduct all the tests at room temperature (hopefully on the same day) because temperature has an effect on the rate of the reaction. > Shaking or stirring - I will try to keep jogging of the solutions to a minimum so as not to alter the rate of reaction. However in the experiment, we will assume the temperature as constant and only change one variable, the concentration. Shaking force will also be assumed as constant I predict that "the greater the concentration of Sodium Thiosulphate in the solution the faster the chemical reaction will take place." ...read more.

Middle

Safety To conduct my experiment safely I will follow normal laboratory rules, which include: > The wearing of safety goggles to protect my eyes from chemical splashes. > Standing up to conduct the experiment, therefore reducing the risk of tripping and spilling chemicals. > Taking care when handling chemicals, particularly Hydrochloric acid and Sodium Thiosulphate because they are irritants. I will not touch my eyes or mouth until I have thoroughly washed my hands. Variable Control To make this experiment a fair test I will only vary one thing - the concentration of the Sodium Thiosulphate solution. I will conduct all the tests at room temperature, as said which will be considered constant even though there may be a slight effec on the results. The measures of Hydrochloric acid will all be the same (5 cm�). The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock. Results: Test 1 Concentration (g/1000cm�) Time (s) 40 31 30 41 20 131 15 209 10 238 5 410 Test 2 Concentration (g/1000cm�) Time (s) 40 32 30 45 20 122 15 201 10 248 5 398 Average Concentration (g/1000cm�) Time (s) 40 31 30 43 20 126 15 205 10 243 5 404 The results were taken to the nearest second due to the fact that the timing was being done by human recognition, so can never be definite. ...read more.

Conclusion

The problem comes when using the overall average that any anomalous results that are included to produce this average make it less accurate and so less dependable. Increasing the chance of error and the need to do the experiment again. The results seem reliable but as I have said there is a list of variables that have not been totally taken in to account. Because I am basing my interpretation of their reliability on a hypothesis and my own personal view it is hard to tell. I see them as reliable but if my views and hypothesis are wrong then the results are not reliable. I would need more time to research this further in order to make a firm decision. A potential answer to some of the problems would be to keep the solutions in a carefully controlled environment, and to use colormetric analysis to see when the solution has reached a certain colour therefore making the test fair. To extend this work one could look into the affects of catalysts (and other variables) on reaction times or you could try the same experiment with different substances or by varying the amount of acid instead. Test 1 Concentration (g/1000cm�) Time (s) 40 31 30 41 20 131 15 209 10 238 5 410 Test 2 Concentration (g/1000cm�) Time (s) 40 32 30 45 20 122 15 201 10 248 5 398 Average Concentration (g/1000cm�) Time (s) 40 31 30 43 20 126 15 205 10 243 5 404 ...read more.

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