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The Effect of Concentration On the Rate of a Reaction

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Investigation: The Effect of Concentration On the Rate of a Reaction Introduction: When dilute hydrochloric acid is added to a solution of sodium thiosulphate a reaction takes place according to the following equation. Na2 S2 03 (aq) + 2HCL (aq) + 2S(s) + H20(l) +SO2 (g) The reaction can be followed by measuring how long it takes the precipitated sulphur to obscure a cross marked on a piece of paper. Factors which might affect the reaction 1. Temperature of the reaction 2. Concentration of the sodium thiosulphate 3. Concentration of Hydrochloric acid 4. Light intensity The factor I will change if the concentration of the Hydrochloric acid. Prediction I predict that as I make the concentration of acid less and less the rate of reaction will be slower. If I double the amount of acid the reaction time will become twice as fast. Explanation for prediction I think that this will happen because as I lower the concentration of the acid there will be less and less acid particles for the thiosulphate particles to collide and react with. ...read more.


Then I will ad the hydrochloric acid which is of varying amount. I'll swirl the mixture then start the clock. I'll look down into the conical flask till the cross disappears. When it does I will stop the clock. I will repeat it 3 times for each amount of acid. I'll put the results in a table and work out the averages. Safety To keep myself safe I will make sure that none of the chemicals come into contact with my skin. I will make sure that I don't breath in too Much of the fumes from thiosulphate as they are corrosive and can be can be dangerous to people with asthma. Solution Vol of thio (cm ) Vol water (cm ) Vol. of acid Time for the cross to diss-appear Ave time A 60 0 60 24.05 21.87 21.55 22.49 B 60 10 50 20.60 21.06 24.14 21.93 C 60 20 40 22.21 23.84 18.72 21.59 D 60 30 30 20.50 20.03 22.20 20.91 E 60 40 20 26.40 36.00 35.26 37.07 F 60 50 10 57.22 54.07 49.22 53.50 Analysing the results As I diluted the acid the reaction time gets slower. ...read more.


The experiment could be done again because we had to tell when the cross was gone with out eyes. We could do it again with a device which could detect when it has disappeared. To make the results even more accurate we could have taken more for each section or we could have changes measurements in a different scale. We could have taken 5 readings for each one rather than 3 and we could have changed measurements in 5cm and not 10cm . I think that we would get the same pattern of results if I repeated the experiment. Maybe not the exact results but the pattern would remain the same. I think I took enough results to be certain but in a perfect world I would like to repeat the experiment at least one more time. To be a really fair test I would have liked to have used acid and thiosulphate from the same batch but others were using it too so this wasn't possible. To provide extra results I could do more of the experiment and other people could do it also. ...read more.

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