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Investigating how changing the concentration of hydrochloric acid affects the rate of its reaction with magnesium metal.

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Introduction

Investigating how changing the concentration of hydrochloric acid affects the rate of its reaction with magnesium metal. Introduction: During a chemical reaction, old bonds are broken and new bonds formed thus creating a new substance. In order for bonds to be broken there must be a supply of energy, however, when bonds are formed energy is released. This means that bond breaking is an endothermic reaction and bond forming an exothermic reaction. This bond breaking and forming can be done faster or slower depending on the rate of the reaction. The rate of a reaction is dependent upon the number of collisions the molecules have in any set time. This is the theory I shall be testing in this experiment. To test this I must take into consideration the factors which affect the rate of reaction. The main ones are: Concentration of the reactants, for instance if I had a lower amount of hydrochloric acid the reaction would be slower because concentration affects rate; the temperature at which the reaction takes place, for example most reactions happen quicker at higher temperatures but if I was experimenting with an enzyme the reaction would work best at a certain temperature like 37?c for body enzymes; surface area of the magnesium, i.e. ...read more.

Middle

The accuracy of this method depends upon the accuracy of the balance as the change is often minimal. Lastly the volume of gas, which is the method I used, involves the use of a gas syringe to measure the amount of gas given off. It is one of the simplest ways but, as with the others is possible to lose accuracy depending on how fairly you carried out the test. If, after putting the Mg metal in with the acid, I do not put the bung on top of the flask quick enough it could change the results. There fore I must ensure the bung is placed on top of the flask as quickly as possible. Fair test: To keep this test fair and safe I must keep certain elements in mind. For example I must ensure that the concentration of the hydrochloric acid is changed at regular intervals so I can make sense of my results and formulate a conclusion from them. I must also make sure that I sandpaper the magnesium every time so that I remove any impurities which may affect how quickly the magnesium reacts with the acid but I mustn't do it too hard or it will interfere with the magnesium. For example the extra layer of impurities may be different for each piece of magnesium and would consequently make my test unfair. ...read more.

Conclusion

The graph is steeper at the start because the reaction is increasing quicker at the start than it is toward the end and the magnesium is beginning to be used up in the reaction so the rate will slow down as there are less particles for the acid to collide with. Evaluation: This experiment is quite hard in some ways because there are so many things that could change the results that are hardly noticeable, for example a couple of degrees higher might change the number of collisions and ruin an experiment. That is why I suggested doing the experiment a couple of times and finding an average of the results. After doing this experiment I realised it would have been wiser to take the results down every five seconds instead of ten, because in some of the higher concentrations the rate went too fast and we had to only do a minute so only got 6 results. However, had we been doing it every five seconds we would have got more results, although it may have been harder to check it every five seconds exactly. The odd results, as highlighted in my graphs, are most probably caused by gas being lost at the beginning of the experiment because I may not have put the bung on quick enough. Page 1 Chemistry coursework 18th of July 2001 Katy McManus Year 10 ...read more.

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