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Investigating how concentration affects the rate of reaction

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Introduction

Investigating how concentration affects the rate of reaction Aim To investigate how changing the concentration of hydrochloric acid (HCl) affects the rate of reaction when reacted with magnesium ribbon (Mg.) The chemical word equation for this reaction is Magnesium + Hydrochloric acid ? Magnesium Chloride + Hydrogen. The chemical symbol equation is Mg + HCl ? MgCl2 + H2. Prediction When the magnesium reacts with the hydrochloric acid, it is expected that the rate of reaction increase as the concentration of the acid increases. (Co-ordinated Science, 'Gallagher & Ingram.) When experimenting how concentration of a reactant affects the rate of reaction, the result fits into one of three orders of reaction. 0 order graph Rate/ cm3s-1 Concentration/Molar For a zero-order reaction, the rate of reaction remains constant and nothing will happen to the rate however much the concentration is altered. 1st order graph Rate/ cm3s-1 Concentration/Molar For a first-order reaction, as the concentration increases the rate will increase proportionally. For example, if the concentration was doubled, so will the rate of reaction. 2nd order graph Rate/ cm3s-1 Concentration/Molar For a second-order reaction the rate is the square of the concentration. For example, if the concentration were 2[m,] the rate would be 4 cm3s-1 ('A' Level Chemistry Second Edition EN RAMSDEN.) ...read more.

Middle

From the experiment, the main things that are being tested for are the time taken for the reaction and the volume of hydrogen produced. This much information is then enough to find the rate of reaction. Rate = Volume / Average Time. By keeping it a fair test, the amount of reactant is always constant because an increasing amount means more particles and more successful collisions affecting the rate. Also, the surrounding temperate should be about constant; with a high temperature the particles move around more quickly. This causes them to collide more often and therefore react more quickly. (Page 66 Chemistry for OCR A by Lees and Payne) The safety measures/precautions taken are to wear goggles as protective eyewear, hydrogen is a flammable gas, also, hands should be washed after the experiment is over and no other chemical should be touched with unwashed hands. Conclusion From the results obtained, my graph shows that when the concentration increases, the rate of reaction also increases. This means the stronger the acid, the faster the reaction, this can be explained using the collision theory. As the concentration increased the particles became closer to one another and susceptible to successful collisions and so a faster rate takes place, my graph shows this. ...read more.

Conclusion

We could improve our method by using a water bath, where the temperature is a constant. This would help us because it would improve accuracy, as the temperature doesn't come into effect. This method would prevent the effect of an exothermic reaction on the overall results. A downfall was that we didn't know exactly when the reaction actually stopped. This was because we were only confirmed that the reaction was taking place by ocassional bubbling and because this is only occasional, when the reaction had stopped in the real world; we were still waiting for another bubble (and once we found out none came, we stopped the stopwatch some 10- 15 seconds later.) If we made this mistake for all the concentrations with approxiamately the same number of seconds later, this wouldn't be an issue but because at lower concentrations there is a low rate; the hydrogen produced is also slower. This decreases accuracy and reliability of the experiement. The method I have used is suitable because it is set in the form of instructions to someone who is about to carry out the experiment. Also, it is formed in bullet points making it more straightforward. When we practically carried out the method it was all done in a logical and organised order repeadedly (9 concentrations, 3 times each) ...read more.

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