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Safety To investigate the effect of concentration on the rate of reaction between sodium thiosulphate (Na2S2O3 ) and hydrochloric acid.

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Chemistry Coursework - Rates of reaction Aim Safety To investigate the effect of concentration on the rate of reaction between sodium thiosulphate (Na2S2O3 ) and hydrochloric acid. As we know, acids are very dangerous chemicals; therefore, precautions need to be taken to avoid accidents while conducting this experiment. To ensure that this experiment is carried out safely, safety goggles should be worn at all times to prevent damage to the eyes in the case of an accident. Scientific Information The rate of a chemical reaction can be followed by measuring the rate at which the products are formed or the rate at which the reactants are used up. This allows a comparison to be made of the changing rate of a chemical reaction under different conditions. The speed (rate) of a chemical reaction increases :- A) if the temperature increases B) if the concentration of dissolved reactants or the pressure of gases increases C) if solid reactants are in smaller pieces (greater surface area) D) if a catalyst is used Temperature If the temperature increases, the rate of reaction speeds up. The particles will carry more kinetic energy, which means they will move faster. This means that the particles will collide more often as the collision frequency is increased. The collisions will have more energy than the activation energy; hence the reaction will speed up. ...read more.


I repeated the results of my experiment to make sure that they could be as accurate as possible. I did this three times for each concentration of Sodium Thiosulphate and looked for any anomalous results in my reading. The readings I obtained from my preliminary work are shown in the table below. Concentration Of Sodium Thiosulphate (m) 0.50 0.75 1.00 1.25 1.50 Reaction Time (s) 8 9 10 7 6 The table shows the concentration of Sodium Thiosulphate and the time it takes for it react with Hydrochloric Acid. This table does not coincide with what I originally thought would happen to the reaction time. I expected the reaction time to decrease as the concentration of the Sodium Thiosulphate solution increased, but obviously, this isn't the case, because the reaction time also increased. It only does this until the concentration of Na2S2O3 reaches 1.25m, then it starts the initial task of decreasing in time. There could be a number of factors that made my results incorrect. One of which is using a stronger concentration before a weaker one and not washing out the flask properly. This causes a stronger concentration of Na2S2O3 in the beaker, which may speed up the reactions. Another factor may be that, when I washed the beaker, there may still have been traces of water inside, that could dilute the solution and make the reaction time increase. ...read more.


- Secondary source Britannia Interactive Encyclopaedia 2002. Evaluation My experiment went according to plan but there were flaws in it. I think there is a human error factor involved when you are measuring liquids and looking for an end point in the reaction. Although the reaction I chose had a fairly definite end point it was still hard to tell whether the whole cross had disappeared or not. Instead of using a cross a light beam could be used and when the beam goes out that is the end point. A better standard of measuring cylinders and pipettes could be used. My results seemed reliable but you always have to consider more. Because I am basing my interpretation of their reliability on a hypothesis and my own personal view it is hard to tell. I see them as reliable but if my views and hypothesis are wrong then the results are not reliable. I would need more time to research this further in order to make a firm decision. I think that our original idea of using a computerised light sensitive device was a good idea. I feel that with more time I could develop a way to let me use this. The results that I could get from this (if it worked) would be more reliable and 'strong'. To extend this work one could look into the affects of catalysts (and other variables) on reaction times or you could try the same experiment with different substances or by varying the amount of acid instead. 1 Richard Mahorn ...read more.

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