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# How does varying the concentration in a reaction affect the rate of reaction?

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Introduction

How does varying the concentration in a reaction affect the rate of reaction? Introduction To investigate how concentration affects the rate of reaction, I shall be reacting magnesium with hydrochloric acid. I will keep the length and weight of the magnesium the same and will change the concentrations of the hydrochloric acid. Fair testing To make it a fair test, I will keep the length and weight of the magnesium the same at all times. I will change the concentrations of hydrochloric acid and I will measure the volume of hydrogen produced. At all times during the experiment, I will stop the stopwatch when the volume of hydrogen produced reaches 20cm3. Preliminary Experiments Experiment 1 An experiment was set up in which a 3cm strip of magnesium was reacted with 1M of hydrochloric acid. The aim was to set up the actual experiment and to time how long it would take for certain volumes of hydrogen to be produced from the reaction. This would mean I could make a decision on how I would conduct my own experiment. Firstly, the magnesium was placed inside the hydrochloric acid. The bung was closed and after every 5 cm3 of hydrogen produced, the time was recorded. These were the results obtained from the experiment: Volume of hydrogen produced / cm3 Time / s 0 0 5 7 10 10 15 13 20 16 25 19 30 22 35 34 45 36 As ...read more.

Middle

This is because there are more successful collisions. This happens because there are more hydrochloric acid molecules for the magnesium atoms to collide with. This increases the chance of successful collisions. Graph 2 shows that as the concentration increases, the rate of the reaction is quicker. This is because the particles in the reaction collide but only some of these are successful. For a successful collision to happen, the particles need activation energy. When they have enough activation energy, they are able to break existing bonds and make new ones, which in this case is hydrogen. When I increased the concentration of the hydrochloric acid, the particles in the reaction were closer together (because the volume of acid stayed the same). This increased the likelihood of collision, which therefore increased the chance of successful collisions. My proof of this was that it took less time for 20cm3 of hydrogen to be produced as the concentration increased. However, my second graph clearly shows that the line is curving upwards. This means that as the concentration increases, the rate of reaction increases as well, but at a greater rate each time. This can be explained by a preliminary experiment that I did. In that experiment, I found out that from the start of the reaction to the end of the reaction, the temperature of the reaction increased by 1oC. ...read more.

Conclusion

If there was more than 100cm3, then there would have been more collisions and if there was less, then there would have been fewer collisions. This would have affected my time measurements. * Lastly, I could not control the temperature of the reaction. If the temperature increased, the rate of reaction would have been quicker. If it decreased, the rate would have been lower. However, I do not think there would be a realistic way of avoiding this problem. A way I could have improved my experiment would have been to use the same volume of hydrochloric acid and the same length of magnesium each time I did the experiment. I could make the volume more accurate by using a more accurate measuring cylinder. A way to improve the accuracy of the magnesium would be to have someone hold one end of the magnesium and then I would cut it 3cm in. This would improve the accuracy because the first time I did it, the magnesium may have moved while I was cutting it and I may have cut the wrong length. Another problem with my experiment was that I could not keep the temperature constant. A way to see how temperature changes during an experiment would be to investigate how temperature affects the rate of reaction. I could do the same experiment but I would use a water bath to control the temperature. This is what my results table would look like: Temperature / oC Time / s Rate of reaction / s-1 ?? ?? ?? ?? ...read more.

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This is a well structured laboratory report. The data collected is of a reasonable quality. Specific strengths and improvements have been suggested throughout.

Marked by teacher Cornelia Bruce 17/04/2013

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