Investigating Factors Affecting the Rate of a Chemical Reaction
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Manaan Malik 5f presents... Mr Phillips- Chemistry "INVESTIGATING FACTORS AFFECTING THE RATE OF A CHEMICAL REACTION" Introduction I will be conducting an experiment investigating two different factors that can affect the rate of reaction in a chemical experiment. The reactants, which I will be experimenting with, are HYDROCHLORIC acid (aq) and SODIUM THIOSULPHATE (aq). With rate meaning the speed of the reaction. We know that there are many factors that can affect this, such as; * Surface area * Concentration of reactants * Temperature of the reactants * Catalyst * Light * Mixing From this list I must choose two suitable factors affecting rate of reaction to investigate. I will be looking for the most practical and which factors would hopefully give us the most varied set of results. As for the other factors, which I'm not investigating but could affect the rate, these must be controlled. The effects of, and controlling, the factors. Catalyst- The job of a catalyst is to weaken bonds and therefore lower the activation energy thus increasing the rate of reaction as it makes it easier for both reactants to react. I will control this by making sure there is no catalyst present. Light Intensity- light intensity will have little effect on the rate of reaction so therefore I will take minimal caution in controlling this factor. I will simply carry out my experiment under the same light intensity throughout by staying in the same place and not switching the lights on and off. Mixing- when two liquids are reacting very little mixing is required, as no substance needs to be dissolved. However no mixing could make the rate of the reaction longer so I will control this by mixing a little as soon as the reactants meet. Further mixing will have no effect on the rate of reaction. I have decided to investigate varying the concentration and temperature of the reactants. This will give me a more varied set of results then light intensity and mixing hopefully.
So from; 20-30oC rate increase 0.008s-1 30-20oC rate increase 0.007 s-1 40-50oC rate increase 0.006 s-1 50-60oC rate increase 0.030 s-1 60-70oC rate increase 0.032 s-1 The first three have an average difference of 0.007 s-1 yet the last two have an average difference of 0.030 s-1. My original prediction was that if you increase the temperature of a reaction, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where at room temperature, the time for the cross to disappear was 274 seconds and at 70oC the time for the cross to disappear was 11 seconds - a difference of about 263 seconds. Thus when Hydrochloric acid was reacted with Sodium Thiosulphate the particles in the solution were moving around with more energy; enough to break the energy barrier and for a reaction to occur as the temperature rose. Evaluation I think that this experiment has gone very well. My results were of a particularly accurate standard as I did each temperature the reaction was taking place twice and calculated an average from these times. There were no strange results (anomalies) within my results table although I didn't get the exact results I expected. I found that during the last two temperatures the rate was much increased. Reliability of results can only be shown by repeating the experiment a number of times. I could have therefore improved upon the reliability of my experiment by repeating the experiment 10 times. The reason this was not done initially was due to time considerations that are imposed in a classroom situation. Accuracy of my results was dependant upon my observations so I may have introduced an error into the results.
This is because my judgement of the cross disappearing may differ to another students, so were they to repeat my practical they may not obtain results which tally with mine. This however does not effect the overall analysis of my practical as I alone judged when the cross had disappeared therefore negating the error. In order to obtain results which are of a more accurate nature I could have used a light meter to judge the intensity of the precipitate formed. I believe that I did get a suitable range of results for this experiment. I recorded results from concentrations that ranged from 0.03moles/dm3 to 0.15moles/dm3 and I think that this is quite a good range to see how concentration affects the rate of reaction. Some areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of sodium Thiosulphate and hydrochloric acid. There is lots of room for human error here. For example I could have used a burette for measuring the HCL or Thiosulphate rather than using a measuring cylinder. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment. In a final conclusion this investigation has been a very successful one. I feel my results and analysis have been as accurate and reliable as they could have been under the time allocated. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables i.e. adding a catalyst. These are the ways that I could expand on the original question. Further work I could attempt is to see if the rate of reaction increases similarly for other reactions, e.g. hydrochloric acid and magnesium ribbon, when the temperature of the reactants is increased or deduce if there is a unique increase in the rate of the reaction for individual reactions with temperature variation. I could also see if my quantitative prediction for concentration also held true with other reactants such as Magnesium and Hydrochloric acid etc.
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