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Rates of Reaction

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Rates of Reaction Coursework Investigation: to find out how the rate of reaction is affected by changing concentration Aim: To find out how changing the concentration of sodium thiosulphate solution affects the rate of reaction when it is mixed with hydrochloric acid. I am going to do this experiment by adding different concentrations of sodium thiosulphate into a constant concentration of hydrochloric acid (2M). To make the different concentrations of sodium thiosulphate I will mix 4% sodium thiosulphate with distilled water, this will ensure that I do not get any other substances into my mixture when I am changing the concentration Word Equation: Hydrochloric acid + Sodium Thiosulphate sodium chloride + sulphur dioxide + sulphur + water. Symbol Equation: 2HCl(aq) + Na2S2O3(aq) 2NaCl(aq) + SO2(g) + S(s) + H2O(l) Chemicals and apparatus: A 100ml conical flask A 50ml measuring flask A paper cross A stirring rod A thermometer A stopwatch 2M hydrochloric acid Distilled water 4% sodium thiosulphate solution Variables: Independent -The independent variable in this experiment is the concentration of sodium thiosulphate solution because I will be changing it throughout the experiment Dependent -The dependent variable in this experiment is the time it takes for the hydrochloric acid to react with the sodium thiosulphate solution. ...read more.


50 40 30 20 10 Volume of distilled water (cm3) 0 10 20 30 40 Fair Test: I am going to make this a fair test by making sure that I use the same volumes of hydrochloric acid for each run. I will make sure that all of my measurements are exact by placing the measuring cylinder on a flat surface at eye level when I am measuring out my chemicals. The Collision Theory: The collision theory states that for a reaction to occur the reactant particles must collide with kinetic energy for the reaction to take place, but only some of the collisions that occur between reactant particles will react because some will not have enough kinetic energy to produce a reaction. Reaction A Reaction B HCl particle Na2S2O3 particle As you can see, the chances of a successful collision taking place in reaction B, where the concentration of the reactants is greater, is more likely than in reaction A because there are more particles to collide with. Prediction: I predict that as the concentration of sodium thiosulphate increases the reaction time will decrease. This is because the more concentrated the sodium thiosulphate solution is the more sodium thiosulphate particles there will be to react with the hydrochloric acid particles and therefore the more ...read more.


The graphs showing the average time taken for each concentration of sodium thiosulphate backs up what I thought would happen in my prediction because if the average time taken for the reaction to take place decreases as the concentration of sodium thiosulphate increases it is reasonable to assume that the rate of reaction also increases. The rate of reaction graph also backs up what I said would happen in my prediction, I thought that as the concentration of sodium thiosulphate solution increased so would the rate of reaction, my graphs show that this is correct. Conclusion: Overall I think that this experiment worked well. However I think that I could improve it next time by * Using more concentrations of sodium thiosulphate, such as 1.5%, 2.5% and 3.5% as well as the concentrations that I used for this experiment. This would mean that I would get more accurate results for the experiment. * I would also create another graph showing each of the individual reaction times taken so that I could compare them and see how accurate my results were for each concentration. I found that changing concentration affects the rate of reaction by increasing the rate of reaction if the concentration is increased, or decreasing the rate of reaction if the concentration is decreased. This is what I predicted. ...read more.

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This is a reasonably well written report. It covers the majority of factors necessary for this type of investigation. Specific strengths and improvements have been suggested throughout.

Marked by teacher Cornelia Bruce 18/04/2013

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