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Rates of Reaction Investigation - Magnesium Ribbon

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Introduction

GCSE CHEMISTRY COURSEWORK This chemistry coursework requires an investigation to see how long it takes for magnesium ribbon to be eaten away by hydrochloric acid. Before starting the investigation, I decided to do some research about magnesium and hydrochloric acid. Magnesium is a light, shiny grayAim I plan to investigate the effect of concentration of acid, in the reaction between dilute hydrochloric acid and magnesium ribbon. The rate of a chemical reaction is a measure of how fast the reaction takes place. It is important to know that a rapid reaction is completed in a short period of time. Some reactions are very fast, for example; the formation of silver chloride precipitates when silver nitrate and hydrochloric acid solutions are mixed. In this investigation I will test different concentrations of acid reacting with magnesium. Prediction My prediction is that as the concentration of the hydrochloric acid increases, the time taken for the magnesium to disappear decreases. I predict that when the concentration of the hydrochloric acid doubles, the rate of the reaction doubles. Linking prediction to theory Reaction rate and concentration. The collision theory describes how the rate of reaction increases (the time taken for the magnesium ribbon to disappear when it is reacted with hydrochloric acid) when the concentration of HCL increases. As the reaction continues, the concentration of the reacting substances decreases and so does the rate of reaction. The reaction is speeded up if the number of collisions is increased. The higher the concentration of HCL you use, the less time it takes for the magnesium to disappear and so the rate reaction increases. If the activation energy is high only a small amount of particles will have enough energy to react so the reaction rate would be very small, however the activation energy is very low the number of particles with that amount of energy would be so high, so start, so the reaction rate would be higher. Apparatus Hydrochloric acid(3 mole) Water(to dilute acid) 10ml testube magnesium(2cm long) ...read more.

Middle

Also, because the particles are moving faster a larger proportion of the collisions will exceed the activation energy and so the rate of reaction increases. 5. The rates of some reactions are increased by exposure to light. Light has a similar effect as temperature because it produces heat. 6. A catalyst is a substance, which can alter the rate of a reaction but remains chemically unchanged at the end of the reaction. Catalysts usually speed up a reaction. A catalyst, which slows down a reaction, is called a negative catalyst or inhibitor. Catalysts speed up reactions by providing an alternative pathway for the reaction, i.e. one that has much lower activation energy. More collisions will, therefore, have enough energy for this new pathway. Extracts from: Letts Study Guide, GCSE CHEMISTRY. All this information is relevant to my investigation, as I now know what would happen to the molecules when using different variables. It also makes it easier to decide what variable I am going to use in this circumstance. I decided to use the concentration of acid as my variable. I used 5 different strengths of hydrochloric acid. These strengths would determine the rates of reactions. I decided to measure the acid in millilitres. I predicted that the higher the concentration of the acid, the faster the reaction between magnesium ribbon and the hydrochloric acid. This would be because there were more acid molecules to react with the magnesium ribbon. I decided that I would do 5 experiments and the different concentrations of hydrochloric acids were: v 1.0 molar v 1.25 molar v 1.50 molar v 1.75 molar v 2.0 molar Before doing the actual experiment I decided to do some preliminary work. These were to tell me the details that I would need to know for my investigation to be successful. I saw from these preliminary investigations that the magnesium ribbon started to react with the hydrochloric acid the moment that I dropped it in. ...read more.

Conclusion

This may have affected the rate of reaction, as water would dilute the acid. To improve my results, I could dry the test tubes and the measuring cylinder after they are washed to prevent diluted acids. The size and weight of the magnesium would have affected the rate of reaction. The experiment could be improved by measuring, adjusting and weighing the magnesium ribbons so they all are the same size and weight. I also found out from background information, that the magnesium ribbon is covered with a whitish deposit. This deposit was magnesium oxide where the magnesium had reacted with the air. I would imagine that some pieces had only a little of this oxide and some had a lot. The pieces of magnesium ribbon that did not have much oxide on them reacted faster than those with a lot. To improve my results, I could clean the magnesium oxide of all the magnesium pieces using some sandpaper, and this would mean that the acid would not have to eat through the magnesium oxide before reacting with the magnesium. In my investigation I also measured the temperature to see if there would be any change in the rate of reactions. From my results it was noticeable to look at each experiment and see how the temperature had affected the rates of reactions. For instance, if we refer back to the table on page 5 and look at experiment 5, test three is slightly faster than test 1 or test 2 because it has a temperature of 21�, where as the other two tests both have a temperature of 19�. To improve my investigation I could assure that the temperature was constant all the time. I could also do more readings to get nearer to a more accurate result. In my investigation I used concentration as my variable. To improve my investigation further, I could use other variables such as, surface area, temperature, pressure for gas, and a presence of a catalyst. These variables would hopefully prove that they all help speed up a chemical reaction. ...read more.

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