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The effects of concentration on reaction rates

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Introduction

John Saunders (11R) The effects of concentration on the rate of reaction between magnesium (Mg) and Hydrochloric acid (HCl). Introduction: In this experiment, I am going to find out what happens when different concentrations of hydrochloric acid are mixed with the same amounts of magnesium. The probable outcome of this is that the reaction will be more vigorous to start with, meaning the reaction would end up being completed faster, if the concentration was to be higher than normal. This would happen because there would be more atoms of hydrogen and chlorine in a higher concentrated solution, to react with the magnesium. As you can see, the circles that represent the hydrogen and chlorine atoms of the hydrochloric acid find it a lot harder to fit inside the right-hand rectangle, that is the same area as the left rectangle (the rectangles representing the solution of acid). This means that the right-hand rectangle is more concentrated, as the hydrogen and chlorine atoms take up more space. If a piece of magnesium were to be placed in the rectangles, then the more vigorous (and faster) reaction would take place in the right-hand rectangle. This is because the magnesium would be confined to the (smaller) area where there aren't hydrogen or chlorine atoms, so the collision rate is likely to be higher. ...read more.

Middle

times descend), I can't analyse the results like this. This is because the different concentrations vary too much, meaning that the differences between each concentration and the preceding one are different depending upon which result you look at (e.g. 0.2M - 0.1M = 0.1M; but 4M - 2M = 2M difference). This is why I have set the 'x' axis on my graph 9the concentration), to reflect this, by using a scale, whereby every 10 little squares represents 0.5M. Analysis: These results show trends, but not in the way I expected them to. The results were pretty accurate, I felt, because apart from one minute at the maximum, the results for each test and its repeat were nearly the same. The plot of results on both graphs representing the two tests and the average results all have the same trends, only these results weren't proportional unlike I predicted them to be. There are basically two proportional lines, involving the points 0.1, 0.2 and 0.5 mole concentrations, and the 1, 2 and 4 mole concentrations. For some strange reason, somewhere between 0.5 and 1 mole concentration, the line's sharp gradient declines, so it looks as if the reactions doesn't have the same speed in contrast to the concentration of HCl it's in. ...read more.

Conclusion

This could have been done either by redoing the tests with more magnesium (a longer strip), or by using less HCl. I would have done this, but the tight time limit meant that I couldn't redo all the tests that I have already done in time, before realising this. Another way my results could have been affected is that because the 0.1 reading took a long time to complete, meaning that I may not have noticed that the reaction had finished straight away. I don't think this happened, though, so I'm not too worried about this. Finally, and this occurred in my second test which could indeed explain my ringed faulty result, I admit, time got the better of me and so I didn't wash out my measuring cylinder out after measuring each concentration of acid. I may have measured smaller concentrations first and these concentrations could have mixed with the one I was using then to not give the mole that I said I was using for this test. To get over this problem, I could either have rinsed out the cylinder before measuring each concentration, or even by sharing cylinders with other people, of which each cylinder would only be used for one concentration. Overall, despite these problems, I don't think I will have made a bad attempt at the experiment, because the results were similar both times and they did follow a trend on my two graphs. 1 ...read more.

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3 star(s)

***
This was a routine task requiring only limited precision to be completed. It used basic equipment and collected a limited amount of data. The data that was collected has limited reliability due to the low nature of repeats. Some comments were made in relation to the accuracy of the data however they were not supported with enough experimental evidence to make them reliable. Some scientific vocabulary was used. Overall this is a three star scientific report. Improvement have been suggested throughout

Marked by teacher Cornelia Bruce 18/03/2013

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