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Rates of Reaction Course Work.

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Introduction

Chemestry Rates of Reaction Course Work Introduction/Aim: This coursework is about the investigation of the effect of concentration on the rate of reaction between Sodium Thiosulphate (Na2S2O3) and Hydrochloric acid (HCL) by simply changing the concentration of Sodium Thiosulphate. I made a set of results which were obtained by using the method of 'precipitation'. This is when the product of the reaction is a precipitate, which clouds the solution. One observes a marker through the solution and measures how long it takes for it to disappear. Plan: In order to make it a fair test the volume of hydrochloric acid had to be kept constant each time (5cm�). What had to be changed was a) the amount of Sodium Thisulphate and b) the amount of water. We decided our total volume to be 55 cm�, 5 cm� of that hydrochloric acid, so the rest consisted of Sodium Thisulphate and Water. To obtain our resultes we used the following "Method": Step 1: After setting up everything we first used a measuring cylinder to measure the amounts of Sodium Thiosulphate, Water and Hydrochlorid acid needed. We put the added amount of water and thiosulpahte (which has to be 50 cm�) into a connical flask which will be placed on a paper marked with a cross ("X"). After that we take the measuring cylinder with the 5 cm� of HCl and pored it into the conical flask. Step 2: The stopwatch was started as soon as the first drop of HCl got in. ...read more.

Middle

Volume of H2O (cm3) Volume of HCl (cm3) Total Volume (cm3) Time (s) 10 40 5 55 26.00 15 35 5 55 23.53 20 30 5 55 12.80 25 25 5 55 10.16 30 20 5 55 10.09 35 15 5 55 7.26 40 10 5 55 6.69 45 5 5 55 5.94 50 0 5 55 5.66 The set of results you can see above were taken during all of the experiments. All of the experiments were repeated 2 times in order to receive correct and accurate results. The next step would be to do some calculations with these results. * During all of the experiments it was made sure that the volume of the total solution was always 55 cm� * In all of the experiments the volume of the hydrochloric acid was always 5 cm� These are the calculations i added to my table of results: Concentration = original concentration x volume of Na2S2O3 /total volume of diluted Na2S2O3 i.e., For 30 cm3 of Na2S2O3 used = 1 x (30/50) = 0.6 M Rate = Mass of solid sulphur formed/time taken = 1/time i.e., for 30 cm3 of Na2S2O3 used = 1/time = 1/10.09 = 0.99 Table of results, including the results of all of the calculations: Volume of Na2S2O3 (cm3) Volume of H2O (cm3) Volume of HCl (cm3) Total Volume (cm3) Concentration of Na2S2O3 (M) Time (s) Rate of reaction 10 40 5 55 20.00% 25.24 0.04 15 35 5 55 30.00% 17.56 0.056 20 30 5 55 40.00% 13.69 0.07 25 25 ...read more.

Conclusion

I didn`t have any anomilus results which proves that the message i have used worked in a sence of successfullness and rilableness. Altough the resulats are ok I still have to say that the procedure could have been more accurate. Especially when you take a look at the measuring devices and the method you`ll realise that they could have been more presice in order to obtain better results. It�s also not very easy to decide when exactly to stop the watch, as it is never really clear when the moment was, when the black cross-disappeared behind the cloudy solution. If i had the chance to do this experiment again i would change, include or put more attiontion on the following points: 1. Try to use better, more accurate equipment that includes: - Glass pipettes instead of plasic ones which were used to measure out the liquit. - A different device to determine when the solution has reached a certain level of cloudiness. I am sure that there are specific devices, which do exactly that. - A little apparatus, which pours the substances into the conical flask, and in the same time start the stopwatch. - More accurate measuring cylinders one can make sure that the volumes of the substance are accurate. 2. I would try and use different chemicals in order to see if it effects the rate of reaction. 3. I would do exactly the same experiments but change the amount of solution taken from each substance. 4. I would repeat the experiment one more time so that i have alltogehter 3 sets which will lead to more accurate results and averages. ...read more.

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