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# Rates of Reaction - Concentration.

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Introduction

Rates of Reaction - Concentration The rate of reaction is the rate of a loss of a reactant or the formation of a product during reaction. Although there are many different variables to test, I have chosen to experiment with different concentrations of hydrochloric acid, with sodium thiosulphate as the constant. Aim This experiment tests how differing concentrations affect the rate of a chemical reaction. It will be done using a simple experiment where one substance is constant and the other is varying. Apparatus For each experiment I will need the following; 150 cm3 2 Molar hydrochloric acid 140 cm3 water 250 cm3 sodium thiosulphate 1 conical flask 1 measuring cylinder 1 stop clock 5 pieces of paper 1 pen Preliminary Work; Prior to this investigation, I conducted a preliminary experiment to determine the strength of my method in terms of accuracy and precision. I decided to test how the temperature of an experiment affects the rate of reaction. Therefore, I got 50 cm3 sodium thiosulphate and 40cm3 hydrochloric acid diluted with 10cm3 water. After pouring the two mixtures into a conical flask I placed it onto a black cross on a piece of paper and timed the time it took for the precipitate of sulphur produced to make the solution seem so cloudy the cross disappeared. The same experiment was conducted at temperature of 10�C, 20�C, 30�C, 40�C and 50�C. ...read more.

Middle

seconds 1 50 none 50 41.36 45.63 44.89 2 45 5 50 45.79 49.56 47.85 3 40 10 50 48.27 52.17 49.54 4 35 15 50 51.64 50.39 50.99 5 30 20 50 52.93 55.15 53.45 6 25 25 50 54.52 57.01 57.13 7 20 30 50 57.08 57.59 59.61 8 15 35 50 61.00 61.23 60.36 9 10 40 50 62.74 64.94 60.43 Graph To plot my graph of averaged results, I first have to find an average of my times in order to gain a more accurate and reliable data set. To do this I use the following formula; Time (1) + Time (2) + Time (3) __________________________ 3 I also have to calculate the rate of each reaction. To do this I use the formula; 1 _______________________________ Time taken for reaction to occur Then I have to calculate the concentration of the hydrochloric acid which goes on my other axis. To do this I take the original 2 Molar concentration and convert that to 40g/dm3. I then have to rearrange numbers to find every concentration 40g/dm3 = 50cm3 hydrochloric acid The formula is as follows; Concentration of previous experiment _____________________________________ * Next volume of acid Volume of Hydrochloric acid Example; 40g/dm3 / 50cm3 = 0.8 0.8 * 40cm3 = 32 g/dm3 Hence: Experiment number Time (average) Seconds Rate of Reaction (1/time) Concentration(g/dm3) 1 43.96 0.0227 40 2 47.73 0.0210 36 3 49.99 0.0200 32 4 50.01 0.0200 28 5 53.84 0.0186 24 6 56.22 0.0178 20 ...read more.

Conclusion

I would be able to analyse differences and compare the two experiments. This would then bring more evidence that the higher the concentration, the faster the rate of reaction. If that wasn't enough, I could go on to record the results for an experiment where instead of having sodium thiosulphate, I would use magnesium. The evidence I have is enough to draw up a suitable conclusion although there are still improvements to be made. For a better idea of how concentration affects the rate of a reaction, I could use a wider range of concentrations so that there is more evidence to analyse and conclude. Next time, I will take more time with obtaining he evidence instead of rushing the work to complete it. That lack of haste was probably the cause of mistakes. I only managed to do three lots of experiments which are still not enough to get a reliable set of results; more would be needed to be satisfactory. This is the reason why there was an inconstancy within my results. I will have to measure the level of precipitate produced during the experiments as in my investigation, I did not measure the level of cloudiness of the solution. This would make the experiment fairer. I think that if better equipment such as a more precise measuring cylinder the flaws would start to decrease. A more accurate timer is needed. We would have more truthful measurements to work. Pipettes of a better standard could be used to make the amounts of solution even more reliable. Jingyi Zhang 10TF 1 ...read more.

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