An Experiment to Investigate the Effect of Concentration on the Rate of Reaction
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An Experiment to Investigate the Effect of Concentration on the Rate of Reaction Shehzad Ali Charania An Experiment to Investigate the Effect of Concentration on the Rate of Reaction Planning 1. Aim This experiment's aim is to discover the effect the concentration of a reactant has on the rate of reaction. We will be using sodium thiosulphate and hydrochloric acid. This is because the speed the sulphur (a product) is produced is quite easy to measure and covers the aim of the experiment sufficiently. To try to investigate the aim, w will change the concentration of the sodium thiosulphate and repeat this twice before taking an average and recording our results. The equation for this experiment is: Na2S2O3 + 2HCl --> 2NaCl +SO2 + H2O + S The word equation for this experiment is: sodium thiosulphate + dilute hydrochloric acid --> sodium chloride + sodium dioxide + water + sulphur 2. Preliminary Experiment The preliminary experiment involved using the chosen substances to try to investigate the rate of reaction. The reagents we chose are sodium thiosulphate and dilute hydrochloric acid. These substances react to produce sulphur as one of the products. We can investigate the rate of reaction by seeing how quickly the sulphur blocks out a cross, marked on a piece of paper, completely. The results are shown in the table below. Temp (?C) Volume of Na2S2O3 (cm ) Volume of H2O (cm ) Volume of HCl (g/l) Concentration of Na2S2O3 (g/l) Time Taken for Cross to Go (s) Rate of Reaction (s )
the number of particles that have sufficient energy to react) then I double the chances of a collision happening. This will therefore mean that the rate of reaction doubles. My prediction claims that there will be a proportional increase in rate of reaction as the concentration increases. Using the Maxwell-Boltzmann theory however I predict this increase will be directly proportional to the concentration increase. This means that if the concentration doubles, the rate of reaction will double and if the concentration triples, as will the rate of reaction (and so forth). 7. Improved Table of Results Temp (?C) Volume of Na2S2O3 (cm ) Volume of H2O (cm ) Volume of HCl (g/l) Concentration of Na2S2O3 (g/l) Time Taken for Cross to Go (s) Rate of Reaction (s ) 50 0 5 40 45 5 5 36 40 10 5 32 35 15 5 28 30 20 5 24 25 25 5 20 20 30 5 16 15 35 5 12 Safety Aspects As we were handling chemicals, it was important to be careful. Goggles had to be worn, as did aprons and the laboratory safety rules had to be observed and carried out. Reliability & Accuracy of Results The results were fairly accurate. They supported the prediction in the respect that the time taken for the 'x' to go increased as the concentration of water increased. However during the experiment the temperature differed slightly, which could have had an impact on the results. Even a small difference in temperature (in this case 1?C) can make a substantial difference to the results. This is a reason the results were not directly proportional as predicted.
I have chosen two problems and thought about a way to solve them. 1. Other substances affecting the experiment 2. Temperature For problem 1, I would close off the top of the beaker being used in the experiment. This would prevent excess gases entering the solution and therefore would not affect the experiment. I though about using a cork top, however realized that it would be difficult to see when the 'X' underneath goes from the top, and so would suggest using a clear plastic or even glass top. For problem 2, because the temperature affects the experiment, I would put the beaker in a thermal insulating box or container and this would keep the temperature constant while not affecting the experiment. Temperature increase meant that the particles would collide more, therefore changing the results. We had no control over the temperature, only a way of measuring it. Improvements to Experiment and Reliability of Results After doing the experiment, I would alter the above 2 issues but also would do more repeats so there can be no issue over doing the experiment wrong. Also I would use a larger range of concentrations as there was only 1 set of concentrations to check the possibility of tripling the concentration to see if it tripled the rate of reaction. The evidence is not reliable enough to support the conclusion as there have been a few problems mentioned already with the experiment. However this experiment, done in closed conditions, could yield the results mentioned in my prediction. To prove the point that concentration and rate of reaction are proportional, this experiment is very reliable as every concentration increase yielded a higher rate of reaction without any exceptions.
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