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Rates of Reaction.

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Introduction

Rates of Reaction Rate of reaction means the rate of formation of a product/disappearance of a reactant, this is useful because we can time the different concentrations reacting with the acid, and give each of them a rate, based on the formula rate = 1/time. Rate of reaction is what we use to measure how quickly a reaction takes to reach a certain point in the reaction in this case it is when it gets to certain cloudiness. In this investigation, we will need to measure the time of the reaction, so we can make a rate for it, to do this we use the formula, - rate = 1/time * 1000, we use the *1000 so that it is a manageable number to plot on a graph if necessary. It is generally measured in time, as this is the only means possible to us; however you must be careful because as heat is a catalyst, it strongly affects the rate as you will see in the results, so we have to try and keep it the same throughout the experiment. The reaction we are studying is very easy to monitor and time. All of the products in the solution dissolve into it (sodium chloride, sulphur dioxide and water), apart from sulphur, which makes the solution go cloudy, and forms a precipitate. This can be written down as s-1for example 15.7 s-1means 15.7 per second is the rate of the reaction. The rate is generally measured by selecting a certain amount of two substances, and finding a suitable way of judging when the ...read more.

Middle

for the experiments, as I can't keep the temperature exactly the same throughout the experiment without using other apparatus such as a water bath. So I decided to start with the concentration of 10 g/dm3, so I collected 25 cm3 of this and also collected 15 cm3 of the hydrochloric acid. I placed a beaker over a mat with a cross drawn underneath, then added the two solutions together, I started timing the reaction straight away, after it had finished, and cross had been completely obscured, I stopped timing it, and rinsed out the equipment. I then went on to using the concentration of 20 g/dm3 as this was double the concentration I used before so therefore the rate would hopefully be doubled, but it does not however matter what order you do the experiments in. I collected 25 cm3 of this, and 15 cm3 of acid, and poured them together into a beaker over a cross, I timed the reaction and when the cross was obscured I stopped timing, I then rinsed out the equipment, I then repeated the experiment but I used the concentration of 40 g/dm3 of sodium thiosulphate as this is double the last concentration I used and will help me when it comes to plotting my results, and will show a clear trend. All experiments were carried out 3 times each and with 6 different concentrations. However it does not matter what order you do the experiments in! Valid Testing i) ...read more.

Conclusion

On the actual experiment itself I think I could have done it a bit better as the results show, There are a few anomalies, if you follow the best fit line, for 20 and 30 g/dm3 of sodium thiosulphate the 20 is below the line of best fit, and the 30 is over the best fit line. These could be anomalous for varying reasons: firstly the measuring cylinders I used are not very accurate, as it is hard to judge exactly the measurements, a way to get over this obstacle would to be to use a syringe, or even better a pipette with precise measurements on it, and so you can get it exactly right. Also it is hard to judge exactly when the mixture is cloudy enough, a good, and probably the best way to get around that is to use a light metre, this way you can set it up as follows: Setting it up this way allows the light metre measurements to go down as the mixture clouds and as it gets to a specific level then the time is recorded, this is the fairest way of testing. From my results I can conclude that when you double the concentration of sodium thiosulphate when it is reacting with acid, then the reaction is doubled, and so on, for example with 10g/dm3 of sodium thiosulphate reacting with hydrochloric acid, the rate is 4.36 and for 20 g/dm3 of sodium thiosulphate reacting without hydrochloric acid the rate is 9.80 these are almost perfectly doubled they are only slightly out due to the fact that we could not get the measurements perfect. ...read more.

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