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How does the concentration of an acid affect the fate of reaction?

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How does the concentration of an acid affect the fate of reaction? Introduction I will be conducting an experiment to find out how the concentration of an acid affects the speed of a reaction. For this experiment, I will be using the reaction of Sodium Thiosulphate and Hydrochloric acid. Sodium Thiosulphate --> sodium chloride + sulphur dioxide + Hydrochloric acid + Water + Sulphur Na�S�O� (aq) + 2HCl (aq) --> SO� (aq) + 2NaCl (aq) + H�O (l) + S (s) I chose to use this reaction especially because of the product Sulphur (s). Because the reaction produces a precipitate; solid sulphur atoms, which makes the product solution go cloudy. This precipitate is very useful for measuring the speed of a reaction. By placing an 'X' below the beaker I am going to put the reactants into, and by measuring the amount of acid that is needed to make the 'X' disappear, I can get an amount which tells me about how fast the reaction took place. This can be used in comparison with acids of different strengths. Background Science A reaction is when one or more substances are changed into different substances. There are four major factors that affect the speed of a reaction; Temperature, Concentration, Catalyst and Pressure/Concentration. ...read more.


I decided to use a Titration system for my tests. First, I filled a burette with Hydrochloric acid. I then put 30cm? of Sodium Thiosulphate into a conical flask, and put it below the burette. For the tests, I put 0.5cm? of Hydrochloric acid into the Sodium Thiosulphate, stirred it, and then waited 15 seconds before putting 0.5cm? more Hydrochloric acid into the Sodium Thiosulphate. This was to allow time for the reaction to end. I did this until the 'X' on the bottom of the beaker of Sodium Thiosulphate was no longer visible. I did this 3 times, with 5 strengths of acid: 0.5 moles, 1 mole, 1.5 moles, 2 moles, and 2.5 moles of Hydrochloric acid. These were the results: Test 1 Test 2 Test 3 Average 0.5 Molar Acid 4.5cm? 5cm? 4cm? 4.5cm? 1 Molar Acid 3cm? 3.5cm? 3cm? 3.25cm? 1.5 Molar Acid 2.5cm? 2.5cm? 2cm? 2.5cm? 2 Molar Acid 1.5cm? 1.5cm? 1.5cm? 1.5cm? 2.5 Molar Acid 1cm? 1.5cm? 1cm? 1.25cm? Analysis In the tests, I used hydrochloric acid in strengths of acid of 0.5, 1, 1.5, 2 and 2.5 moles. The theory of Avogadro's constant claims that there are 6 x 10�� atoms in one mole of any substance. If I apply this to the acids I am using, I can work out that the 5 strengths of acid have the following number of atoms in them (respectively); 3 x 10��, 6 x 10��, 9 x 10��, 1.2 x 10�? ...read more.


my results all clearly fit a pattern, and all lie along the line of best fit. There were anomalous results. Because of this, I think that none of the results need to bee repeated. I believe that the differences between the repeated tests were not substantial enough to claim that the results were not sufficiently reliable, seeing as they were all relatively close to each other. I believe that I covered a sufficiently large range of results that are accurate enough to justify the conclusion. The only problem I had with the method I used was to do with the quality of equipment. The burette that I used was not of the highest quality, and so it was hard to release exactly the right amount of hydrochloric acid into the Sodium Thiosulphate. However, it was possible, if slightly tricky. My results were judged by eye, so they may not be as precise as they would be if they had been electronically measured. The divisions on the burette were 0.1cm�, which was definitely small enough for the experiment I was conducting. However, I did not use this measurement; I measured in 0.5cm�. I did this because I believed that 0.1cm� was too small to have any real effect in a reaction. If I was to try and improve the reliability and accuracy of my results, I would simply use higher quality equipment. Languages ?? ?? ?? ?? Science Coursework Oliver Robertson-Glenn Page 1 of 1 ...read more.

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Response to the question

Response to question:
The student has answered the question to the extent that he/she has produced an experiment to prove that the concentration of an acid does affect the rate of the reaction. The student has gone to many efforts ...

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Response to the question

Response to question:
The student has answered the question to the extent that he/she has produced an experiment to prove that the concentration of an acid does affect the rate of the reaction. The student has gone to many efforts to describe the procedure of the reaction and has described everything well, giving appropriate reasonings to many of his/her choices. However, the student does not specifically answer HOW the concentration of the acid affects the rate of reaction, which is the purpose of the coursework. Also, with all scientific experiments, a prediction is required yet this piece does not include a prediction.

Level of analysis

Level of analysis:
The level of analysis is quite poor in the sense that the results that are included are not analysed or even mentioned in the text, although it is shown excellently on a table and a graph. Analysis is important to a scientific experiment and should be given specifically, describing readings from the table/graph and giving reasonings behind it. This coursework includes none of it. Furthermore, the student has given an overall pattern/correlation which is necessary, but has not expanded further on it, which is also necessary.

Quality of writing

Quality of writing:
This coursework has excellent use of technical terms, and also includes the necessary equations for the process. Sentence structure and spelling is pretty poor in some places and mistakes like missing out capitals at the beginning of sentences occur, which would not be expected of a GCSE student. One particular error is in the title where the word 'fate' has been written instead of rate.

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