Investigating the factors influencing the rate of reaction between Sodium Thiosulphate and Dilute Hydrochloric acid.
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Investigating the factors influencing the rate of reaction between Sodium Thiosulphate and Dilute Hydrochloric acid Introduction In a reaction, the initial materials are called the products, and the result materials are known as products. The time it takes for a reaction to happen in is known as the speed or rate of the reaction. The coursework entails investigating the rate of reaction between Sodium Thiosulphate and Dilute Hydrochloric acid and the effect of different variables on the reaction. When a reaction between Sodium Thiosulphate and an acid, a cloudy, yellow precipitate is formed. To see the time it takes a reaction to occur there will be a measure of the time it takes for the precipitate to occur. Looking through the conical flask with the Sodium Thiosulphate and Hydrochloric acid solution, observing the 'X', until it disappears, will do this. This is when the precipitate has formed. The actual reaction in this experiment is: Sodium thiosulphate + hydrochloric acid ==> sodium chloride + sulphur dioxide + water + sulphur Na2S2O3(aq) + 2HCl(aq) ==> 2NaCl(aq) + SO2(aq) + H2O(l) + S(s) There are a number of factors that alter the speed of chemical reactions; these include temperature, concentration of reactions in solution, pressure in gases, surface area, presence of light, and the addition of catalysts. In the experiment that I will conduct, I will vary the concentrations of the solution, whilst ensuring the rest of the variables are kept constant. The dependant variable will be the rate of the reaction or the time taken for a reaction to be present, all other variables are fixed. Diluting the solutions with water will vary the concentrations of Sodium Thiosulphate.
I chose to vary the concentration so Sodium Thiosulphate. I altered the concentration by diluting the Sodium Thiosulphate, but raised the concentration. The volume of Sodium Thiosulphate was always a total of 40cm³. I ensured that the acid concentration was always 1 mol/dm³ and the volume was 10cm³. 10cm³ of Hydrochloric acid with concentration 1m0l/dm³ and 40cm³ solution of S0dium Thiosulphate with a certain concentration are measured with measuring cylinders and the use of pipettes for accuracy. The Sodium Thiosulphate solution is poured into the conical flask; the stopwatch is automatically started when the last drop is added. When the mixture in the flask has turned sufficiently cloudy to the extent, where the letter 'X' can longer be noticed. At this point, the stopwatch is stopped and the time is recorded. The experiment is repeated with all the concentrations. My findings would obviously have a degree of error and there may be anomalies. However to have valid results, I had to ensure the experiment was fair. I used the same standard for judging when the 'X' has disappeared. I will try to measure at the same distance from 'X', using the same eye so there is a reduction of inaccuracy. I will also ensure the measuring cylinders for pipettes for the Hydrochloric acid and the Sodium Thiosulphate solution will not be contaminated. I will use fixed volumes, temperatures and any other variables that may affect the outcome of this experiment. I will keep this variable constant by avoiding excess heat so I plan to keep the Sodium Thiosulphate at room temperature.
In the experiment, there was no real method for me to realise when the reaction was complete. The method I used in the experiment for my turbidity of the solution was very inaccurate. If I had the opportunity, I would have used a colorimeter. A colorimeter is an electronic device that could detect the turbidity more precisely. It shines a laser through the solution as soon as Sodium Thiosulphate is added. The laser is received by a very sensitive LED on the other side. This LED could be connected to a stop clock, which would stop once the LED stopped receiving direct light. One area, which could have been more controlled, was the temperature. Temperature increases the kinetic energy and probability of collision. This consequently increases the rate of reaction. Therefore, the fact that the experiment was conducted on two different days and the temperatures were probably different my results are less reliable. However, I did use the same conical flask so that variable did not affect the results, I also had no other material present in the experiment and used the same sheet with 'X' on it. To extend the experiment I could use a bigger volume of Sodium Thiosulphate. This would enable the concentration to remain the same for longer, which consequently means the results will be more reliable and the rate of reaction is more accurate. This is because as the experiment progresses the concentration decreases due to the fact the molecules in the Sodium Thiosulphate react so less of the molecules remain. Observing the other variables in the experiment such as temperature; it would enable me to find out what other variables affect the rate of reaction. Sources www.danyey.co.uk www.courseworkbank.com www.wpbschoolhouse.btinternet.co.uk
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