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GCSE Chemistry investigation: the reaction of sodium thiosulphate with hydrochloric acid

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Introduction

Keren Long GCSE Chemistry investigation: the reaction of sodium thiosulphate with hydrochloric acid I am trying to investigate what happens when I change the concentration of sodium thiosulphate in the reaction. I have thought of a way to see how long it takes for the reaction to reach a certain point this point being when the X disappears off the bottom of the flask. I will watch the reaction happen in the conical flask and I will put a black cross underneath the flask. As soon as I mix the liquids together I will start a stop watch, then when I see the cross disappear I will stop it and this will be my measured time, this way I will be able to find out how long the reaction took each time we vary the mixtures. This is what the reaction would be written as: Hydrochloric acid + sodium thiosulphate sodium chloride + sulphur dioxide + sulphur + water. 2HCl(aq) + Na2S2O3(aq) 2NaCl(aq) + SO2(g) + S(s) + H2O(l) ...read more.

Middle

This is collision theory. The two molecules will only react if they have enough energy. By heating the mixture, i will raise the energy levels of the molecules involved in the reaction. Increasing temperature means the molecules move faster. Increasing the concentration of the reactants will increase the frequency of collisions between the two reactants. So this is collision theory again. Although you keep the temperature constant, kinetic theory is relevant. This is because the molecules in the reaction mixture have a range of energy levels. When collisions occur, they do not always result in a reaction. If the two colliding molecules have sufficient energy they will react. The reaction is between two solutions, i might find that the rate of reaction is limited by the concentration of the weaker solution, and increasing the concentration of the other makes no difference. What i need to do is fix the concentration of one of the reactants to excess. Now i can increase the concentration of the other solution to produce an increase in the rate of the reaction. ...read more.

Conclusion

I will have to measure out the volume of each liquid I need to separate measuring cylinders before the reaction. I will then put the acid and water in to the flask before the experiment starts then I will add the sodium thiosulphate solution, then when I put this in I will start the stopwatch and swirl the flask so the solutions mix. When the reaction is over I will wash the flask out because there might be residue of the experiment before in the flask we are using and to get fair results this cannot happen. I will repeat this process for each experiment. I will do my experiments at room temperature because temperature can effect the reaction. Volume of 0.6 mol/dm3 sodium thiosulphate solution (cm3) Volume of distilled water (cm3) Concentration of sodium thiosulphate solution (mol/dm3) Time 1 for X to disappear / seconds Time 2 for X to disappear / seconds 10 50 0.1 256 244 20 40 0.2 129 121 30 30 0.3 76 65 40 20 0.4 65 60 50 10 0.5 50 48 60 0 0.6 41 42 ...read more.

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