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The reaction between hydrochloric acid and sodium thiosulphate.

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Investigation into the factors that affect the rate of a reaction In this investigation, I will be studying the factors that affect the rate of reaction. In this case, the reaction between hydrochloric acid and sodium thiosulphate. Na2S2O3 (aq)+ 2HCl(aq) 2NaCl(aq)+S(s)+SO2(g) When hydrochloric acid is added to sodium thiosulphate, the chemicals react giving solid sulphur as one of the products. This is a precipitation reaction. By watching the speed at which the sulphur has formed, we can find out the rate of reaction. A cross can be marked on a piece of paper, and a flask of sodium thiosulphate can be placed on top. By adding hydrochloric acid to the sodium thiosulphate, we can time how long it takes for the view of the cross to become obscured by the sulphur. We can then find out the rate of the reaction. What is Rate? Chemical reactions can be seen everywhere, whether an explosion, which is extremely fast, to something very slow, like the rusting of a metal. It is not enough just to know whether something is fast or slow however. Rate is a measure of the change that happens in a single unit of time. ...read more.


The graph is likely to look something like this: Apparatus Glass Beaker - This will be used for containing the reactants, a glass beaker will be used, as it is transparent and the cross can easily be seen through the base. Range of measuring cylinders, 10cm3, 25cm3, and 50cm3 - These must be used to measure out the required amounts of reactants. It is good to use different sizes, so that smaller ones can be used for smaller amounts out liquids, to ensure that the measurements are more reliable Sodium thiosulphate - One of the reactants used in the experiment Hydrochloric acid - The Other reactant used in the experiment Cross, marked clearly on a small piece of paper - The cross must be clearly marked, so that it is easy to see from the start of the experiment, and will not be obscured from view too quickly and easily. Safety Goggles - These must be worn to prevent to the eyes from any of the dangerous chemicals being used. Lab Coat - The substances being used can damage clothes, so a lab coat should be worn to protect them. ...read more.


However, this did not affect my results. I am able to tell this, as if the temperature had increased on the second day, there would be a slight jump in the rate of reaction, and this would be noticeable on the graph. Doing the entire experiment on the same day though, would have improved the reliability slightly. I noticed that as the experiment went on, some of the precipitate remained on the sides of the beaker. I'm sure that this hampered the visibility of the cross and no doubt affected the outcome. If I were to do this experiment again I would be sure to thoroughly wash out the beaker after each test. I believe that the evidence I was able to collect is sufficiently good and wide-ranging to support a firm conclusion. I managed to collect six different sets of results, and with this I was able to create a good graph. This number I feel was enough, as the line of best fit on my graph was a straight one and showed no sign of altering. Collecting results using concentrations in between the ones I have used would have been difficult to measure, and the variations in time would have been too short, and of no real significance. ...read more.

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