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Does Concentration affect the rate of reaction?

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Does Concentration affect the rate of reaction? Sodium thiosulphate experiment Plan:- I must produce a piece of coursework investigating the rates of reaction, and the effect different changes have on them. The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. It is measured by dividing 1 by the time taken for the reaction to take place; this is otherwise known as the reciprocal. There are five factors which affect the rate of a reaction, according to the collision theory of reacting particles: Temperature, Concentration (of a solution), pressure (in gases), Surface area (of a solid reactant), and using a catalyst. However, I will go into more detail about these later. I have chosen to investigate the effect concentration has on a reaction. This is because I believe that it is the most practical to investigate - it would take longer to prepare a solid in powdered and un-powdered form, and it is difficult to get accurate readings due to the inevitabilities of human errors (i.e. our reaction rates), and as gas is mostly colourless it is difficult to measure a reaction changing the pressure, also if a substance is added to give the gas colour, it may influence the outcome of the experiment. ...read more.


Fair Test - In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the HCl and sodium thiosulphate will not be mixed up, and will be washed before each use so no mistakes can be made. The water, hydrochloric acid, and the sodium thiosulphate will be measured using a pipette for accuracy; this makes it easier to see if the liquids are even 1 mm off the desired amount, so a precise measurement can therefore be taken. The amount of HCl will be 10 cm each time. I will also take six different concentrations, and repeat each concentration three times; this will hopefully result in consistent results, and will clearly show any anomalies. All of these precautions will make my final results more reliable and keep anomalies at a minimum. This will make my entire investigation more successful. Prediction - I predict that as the concentration of the sodium thiosulphate increases the rate of reaction will decrease. This means that graphs drawn up in my analysis will have positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration is increased. ...read more.


But in this case, due to the probable change in room temperature, this cannot be shown. Evaluating my experiment: Overall, I think that the procedure I have used for this experiment was successful; however, if I was to do it again a monitored temperature would be more appropriate. A way to tackle this problem would be to use a water bath to place the flask into which would keep the solution at a constant temperature. Apart from the results taken for 24cm of sodium thiosulphate, I think the quality of my results is at a high level. As the results show on the "Line of Best Fit" graph, all of the results are very close. This indicates that the teat was a fair one, and the measurements of the solutions were accurate (this is probably a result of using a pipette). A way to improve my experiment further would be to conduct it using computerised equipment, and not by human judgement. This could be done by having a light sensor underneath the flask, so when the solution becomes cloudy and no light reaches the sensor the timer can be stopped at the exact instance it should be. When looking back at my results, I think that I did take enough results, and I think sufficient evidence for this can be gathered from them. ...read more.

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