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Find out how the concentration of a reactant may affect the rate of the reaction in which it is involved

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Introduction

Aims ? To find out how the concentration of a reactant may affect the rate of the reaction in which it is involved. To do this I will need to combine two possible reactants (here, I will use sodium thiosulphate and hydrochloric acid), one of which will be diluted (the hydrochloric acid), and see how long it takes for a change to take place at different dilutions (in this experiment, solid matter or precipitate will form, causing a cross marked on a piece of paper underneath to become imperceptible when the reaction has completed). ? To explore how different degrees of change in concentration affect the rate of reaction, and see if the increase is proportional. Equation The equation for this experiment is: - SODIUM THIOSULPHATE + HYDROCHLORIC ACID = SODIUM CHLORIDE + SULPHUR + SULPHUR DIOXIDE + WATER Na2S2O3 + 2HCl = 2NaCl + S2 + SO2 + H2O (aq) (aq) (aq) (s) (g) (aq) Preliminary Research For this experiment, I will need to research the collision theory, to find out how to write up my method to get the best results while avoiding changes from other variables, and rate of reaction, to find out how to measure and present these results. The collision theory simply states that for a reaction to take place, atoms must strike each other to exchange the electrons necessary. It also states that the faster (only caused by an increase in temperature) ...read more.

Middle

I think 40g/dm3 will take much longer than 8g/dm3, as there will be more interference from the water particles, and so collisions between the reactants won't happen as often. I also predict that the rate of reaction for a concentration of 20g/dm3 of HCl will be half that of 40g/dm3. Variables As discussed in my preliminary research, a number of factors may affect the rate of reaction. These are temperature, surface area, and concentration. In this experiment, I only want to test the effects of concentration on the rate of reaction, and so I need to limit the effects of the other variables. I cannot control temperature, but I will be conducting the experiment at room temperature, which doesn't change dramatically in the short space of time needed to complete the experiment. Surface area does not apply because I am conducting the experiment using aqueous substances. Equipment To complete the experiment and to ensure my safety, I will need to use the following: - ? Conical Flask ? A piece of paper marked with a black cross ? Thermometer ? Sodium thiosulphate ? Hydrochloric acid ? Goggles ? Timer ? Measuring cylinder Diagram Method First I will need to set up the equipment up as in the diagram shown above. I will then don the appropriate safety equipment as discussed on the Equipment list. ...read more.

Conclusion

My results are not very accurate, but in my view it is only the correlation between concentration and rate of reaction that mattered in this experiment, although I would have been able to get more information on the proportion with more accurate results. I feel that the method was a good one, because it was clear and easy to follow. There was, however, one clearly anomalous result. This was probably caused by human error. If I was to try this experiment again, I would place a light sensor in the place of the cross, and if I could, link it to the timer. I would start the timer, and when the sensor detects an absence of light, it would automatically stop the timer. I would also measure the change in mass instead of the formation of precipitate, as it would be more accurate. If I was to try a different experiment to find out more about the effect of concentration on the rate of a reaction, I could react solid magnesium with dilute hydrochloric acid, and then use a gas syringe to measure the amount of hydrogen gas given off over a specified period of time. Sources � www.bbc.co.uk/schools/gcsebitesize/chemistry � CGP GCSE Chemistry Revision Guide Higher Tier Author: Richard Parsons Published in: 2002 ?? ?? ?? ?? Chemistry Coursework: - How does concentration affect rate of reaction? John Pitcher 10AM I ...read more.

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