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Investigation on how the rate of reaction changes as the concentration of an acid changes

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Chemistry Coursework 01 May 2007 Alex Hall (J) Investigation on how the rate of reaction changes as the concentration of an acid changes Skill P : Planning The investigation that we are studying in this piece of Coursework, is how the rate of the reaction between Magnesium and Hydrochloric Acid changes, as the concentration of the Acid is decreased. The equation for this investigation is as follows: Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) I predict that as the concentration of the acid decreases, the rate of reaction will also decrease. Collision Theory says that the more concentrated the reactants, the more collisions will occur. This also explains why the reaction is quickest at the start; it is because the reactants are in their most concentrated state. As the reaction progresses, the concentration of the reactants decreases, and therefore so does the rate of the reaction. In order for the reaction to take place, the particles must collide; and secondly, the smallest amount of energy, the activation energy must be reached. If the activation energy is very high, then there will be a small number of particles able to react, and therefore the reaction rate will be slower. ...read more.


I am going to keep the length of the magnesium at a fixed length of 5cm. From my preliminary work, I can see that the yield of 5cm of magnesium, when reacted with hydrochloric acid, is enough to give me clear results when I come to plot the graphs. * The third and final variable is whether or not I use a catalyst to speed up, or slow down my reaction. A catalyst is a chemical which speeds up (or slows down) a chemical reaction. A positive catalyst lowers the amount of activation energy required, so the reaction happens faster, the catalyst is not 'used-up' during the reaction. For this particular investigation, I am not going to use a catalyst. As I have mentioned earlier, I am going to change the concentration of the acid, by adding water. I will need to make sure that I measure the amount of acid and water correctly. When I add some water to the acid, I will need to be certain that the two liquids are evenly mixed together in the test tube, I will do this by shaking the test tube. ...read more.


* 20 cm� acid + 30 cm� water * 20 cm� acid + 40 cm� water * 20 cm� acid + 50 cm� water The reason behind repeating the experiments is so that if in the first experiment for the lowest concentration, the magnesium is dirty; it may not produce accurate results. So in the next section, I am going to display my tables with the original and repeat experiment, and the averaged result. The graphs in the analysis will make use of the average results. There are a few safety measures that I must take, when conducting this investigation. * We must wear our safety goggles and lab coats. * Hydrochloric Acid may burn clothes and skin if it comes into contact with them. * When the two chemicals are mixed, an impurity may cause a small explosion, so if we are wearing our safety goggles, the chance of anything getting into our eyes is greatly reduced. * Most chemicals are dangerous if swallowed, therefore we must not taste any of the products or reactants, and we must also not put a pen or any other item into our mouths because they may have been in contact with one of the chemicals. ...read more.

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