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In my investigation I am going to look at how concentration affects the rate of reaction, and the reaction I am going to look at is Sodium Thiosulphate (Na2 S2 O3) and Hydrochloric Acid (HCl).

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An Investigation into the rate of reaction is affected by the concentration of a solution The rate of a reaction is the speed at which the reactants change into products. Reactions can be fast and slow for example rusting is a slow reaction and magnesium reacting with oxygen is an example of a fast reaction. There are several factors that affect the rate of reaction these include - ==> Surface area/size of solid particles ==> Concentration of solutions ==> Temperature ==> Presence of a catalyst Aim In my investigation I am going to look at how concentration affects the rate of reaction, and the reaction I am going to look at is Sodium Thiosulphate (Na2 S2 O3) and Hydrochloric Acid (HCl). The equation for the experiment is shown below - Na2 S2 O3 (aq) + 2HCl (aq) 2NaCl (aq) + S (s) + SO2 (g) + H2O (l) In previous times seeing this experiment I have seen what happens, the solution (which is made up of Sodium Thiosulphate and Hydrochloric acid) has become cloudy, this is because the sulphur is precipitated and sulphur is insoluble. In my experiment I am going to time how quickly it takes the solutions of different concentrations to produce solid sulphur, observing how quickly an "X" is observed under a conical flask of solution. ...read more.


Method ==> Prepare a table to record the results of your findings ==> Prepare a measuring tube of 10cm3 of hydrochloric acid and pour this into the conical flask ==> Then measure out 50cm3 of sodium thiosulphate and add this to the beaker. ==> Shake the beaker and start to stopwatch. (Remember to start the stop watch at the same point each time the experiment is carried out as this improves accuracy in the experiment.) ==> Then stop the experiment when the "X" underneath the conical flask is obscured by the sodium thiosulphate and hydrochloric acid solution. ==> Record results ==> Again measure out 10cm3 of hydrochloric acid and pour it into the conical flask ==> But this time measure out 45cm3 of sodium thiosulphate and now add 5cm3 of water, add this to the conical flask, shake and then time ==> Stop the stop watch when the solution has obscured the "X" and again record the results ==> Carry this same procedure out for the following measurements - 50cm3 of sodium thiosulphate and 0cm3 of water 45cm3 of sodium thiosulphate and 5cm3 of water 40cm3 of sodium thiosulphate and 10cm3 of water 35cm3 of sodium thiosulphate and 15cm3 of water 30cm3 of sodium thiosulphate and 20cm3 of water 25cm3 ...read more.


A valid method was used so my results agreed with my theory was used so my results agreed with my theory. We repeated and took the average of three recordings of the experiment and, we also measured the volumes of the hydrochloric acid and sodium to eye level. There were a few problems with the experiment, firstly the same flask was used each time, the flask had obtained a coating of sulphur on it from previous experiments and this was hard to was off. This may affect the results of our experiment as there would be more sulphur added to the solution, which would help to make the experiment go cloudy quicker. Another factor that could of potentially affected results is that the experiment was done over two days which means the temperature of the sodium thiosulphate and the hydrochloric acid could have changed, meaning an increase/decrease in temperature would either speed up or slow down the rate of reaction. Measuring the "X" being obscured by the solution by the eye is not the most scientific method: alternatively a colorimeter could be used. Also measuring cylinders aren't the most accurate piece of equipment for measuring volume: a burette could be used as an alternative. ...read more.

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Generally good data and covers all the main elements needed to secure a high grade. However it is limited by its brief nature. The key elements need to be discussed in more detail with particular care taken to include as much scientific theory as possible. Specific improvements have been suggested throughout.

Marked by teacher Cornelia Bruce 17/04/2013

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