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Factors Affecting the Rate of Reaction between Hydrochloric Acid and Sodium Thiosulphate.

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Introduction

Factors Affecting the Rate of Reaction between Hydrochloric Acid and Sodium Thiosulphate Planning The rate of reaction is the speed in which a reaction takes place. The less time taken for a chemical reaction to complete, the faster the rate of reaction. During a chemical reaction, two or more reactants collide together, break chemical bonds and join again to form products of the reaction. So, the amount of reactants fall as the amount of products rise, thus in inverse proportion. Because of this the rate of reaction is measured by the rate reaction products are produced: Reaction rate = Product_ Time taken Products of a reaction are varied, differing from reaction to reaction, but the amounts can be measured in set ways: Reaction rate = Mass of product formed Time taken = Certain colour change Time taken = Volume of gaseous Product formed Time Taken For the reaction I am going to use, the best method would be to measure the amount of solid product formed over time taken. This is the equation for the reaction Hydrochloric Acid and Sodium Thiosulphate: Sodium + Hydrochloric � Sodium + Water + Sulphur + Sulphur Thiosulphate Acid Chloride Dioxide Na2S2O3(aq) + 2HCl(aq) � 2NaCl(aq) + H2O(l) + SO2(g) + S(s) In this reaction, sodium thiosulphate reacts with hydrochloric acid to form water, salt, sulphur and sulphur dioxide. The two clear reactants become cloudy when added together because of the formation of sulphur, and the solution becomes opaque. This provides a fairly reliable way of measuring the amount of product, and thus measuring the amount of reactant used. Although I could measure the volume of sulphur dioxide gas produced, this would be tricky in comparison to the relative ease of measuring the transparency of the solution. ...read more.

Middle

The results of my preliminary experiment are shown below: Concentration Time taken (mins:sec) 0.10M 0:54 0.08M 1:07 0.06M 1:21 0.02M 3:44 0.01M 5:00 + Overleaf is a sketch-graph of these results to illustrate the curve that I am expecting from my main experiment. From the results I now know that there is no point of using a concentration any lower than 0.02M HCl as the reaction takes too long, and may never produce enough Sulphur precipitate to extinguish the cross. If I take concentrations greater than 0.10M, the difference in time taken between the results becomes progressively smaller and my experiment results would be more liable to error and the trend of data would be more difficult to decipher. For these reasons I will be taking the data range from 0.03M - 0.10M at 0.01M intervals. Each molar concentration used will need to be precise in order for me to find a pattern, so I shall be measuring each concentration out separately from a base of 0.10M acid. 10ml of varying strength acid shall be added to 50ml Sodium Thiosulphate so that the total volume is constant; unlike if varying amounts of 0.10M acid were added which would mean that the total volume would change each time. 10ml of each concentration will be made up, and the ratio of acid to water are shown below: Concentration (M) Ratio (ml 0.10M acid : ml water) 0.10 10 : 0 0.09 9 : 1 0.08 8 : 2 0.07 7 : 3 0.06 6 : 4 0.05 5 : 5 0.04 4 : 6 0.03 3 : 7 Method 1. Gather equipment, Sodium Thiosulphate and 0.10M HCl. ...read more.

Conclusion

Conversely, if the sodium thiosulphate were less concentrated then the constant time would be slower. Thus we can change the maximum rate of reaction by not only changing the concentration of hydrochloric acid but also sodium thiosulphate. There are other variables that have been limiting factors in my experiment that could be examined adjunct to this investigation, some of these are listed below. In my experiment the tests took place at a constant temperature (room temperature), however I expect that varying the temperature will have an effect on the reaction rate. This is because increasing the temperature gives the particles more energy, which means the activation energy is reached easier, and the reaction will take less time to make a certain amount of precipitate. Conversely decreasing the temperature will lengthen the time taken for a reaction. This could be investigated further to find exactly how much effect temperature has on the reaction of sodium thiosulphate and hydrochloric acid. Another factor that may affect the rate could be a catalyst. A suitable catalyst would increase the reaction rate by reducing the activation energy needed for the reaction to take place. Potential catalysts could be investigated adjunct to this work to increase the reaction rate, and to investigate by how much they speed things up. My work would be a lot more accurate if more repeats had been done to replace the erroneous results of test 2, mentioned above. Even so, my work proves that concentration does have a substantial effect on the rate of reaction in the chemical reaction between Hydrochloric acid and Sodium Thiosulphate. As concentration increases, the time taken to produce a set amount of precipitate product reduces up to a certain point where limiting factors limit the decrease in time. ...read more.

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