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Investigation of the rate of reaction of sodium thiosulphate with dilute hydrochloric acid.

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Introduction

tYU2TEb Yordan Agov 5th Chemistry Coursework Investigation of the rate of reaction of sodium thiosulphate with dilute hydrochloric acid I am going to investigate the relationship between the rate of the reaction of sodium thiosulphate with hydrochloric acid. This is the ionic equation of the reaction: 2H+(aq) + S2O32-(aq) SO2(aq) + H2O(l) +S(s) Dilute hydrochloric acid + Sodium thiosulphate + Sulphur dioxide + Water + Sulphur Scientific background All mater made out of tiny particles. Particles, which are of the same matter, attract each other, but if these particles gain enough energy they can overcome this attraction and move freely. This is the state at which particles of a certain matter have enough kinetic energy to stretch their intermolecular attractions to be able to move more freely. Elements or compounds in this state can fit and form different shapes. In this state, all elements and compounds are described as liquids. A meter squared of this matter in liquid form would also be lighter that the same volume of a solid of the same matter as it is less dense and has a lower concentration. This is the state at which particles of a certain matter receive enough energy to completely overcome their intermolecular attraction. Therefore the particles of that matter are virtually not at all attracted to each other, they move independently in random directions. In such a state, elements or compounds can easily fit into different shapes. In this state, matters are also much easier to compress. Matters in such a state are described as gasses. A certain volume of gas would be lighter than that same volume of liquid or solid states of that matter as it is least dense and has the lowest concentration This is the state at which particles of a certain matter hardly receive enough energy to separate from each other. They have low kinetic energy and so their intermolecular attraction keeps them close together. ...read more.

Middle

Every time, on every trial of results the hydrochloric acid and the sodium thiosulphate are being changed for the whole class. It would be good if I could take a whole trial of results at once, surely getting my solutions from the same places. That way I would be sure that my whole set of first results could not have been affected by a different concentration of hydrochloric acid and sodium thiosulphate. Pressure is a variable that could affect the concentration of the solutions but pressure virtually doesn't change at all while I am taking my results. It is a variable that stays constant on its own and that I won't need to control. Temperature is also a variable that could affect the rate of the reaction and therefore it should be kept constant. However we cannot really control room temperature and so perhaps the best thing to do would be to try and take a whole trial of readings in at once when the room temperature would remain constant, because in another lesson the temperature may be different, which means that the results would be different, and so the trial wouldn't be appropriate. A change in temperature in one trial will cause anomalies. Prediction Using my background information and the collision theory, I can predict that the rate of the reaction would be proportional to the concentration of sodium thiosulphate, provided that variables such as temperature and pressure. This is because, even if the concentration of particles of sodium thiosulphate is lower, a particle of a lower concentration of NaS2O32- would be colliding with the same amount of hydrogen ions as a particle of a higher concentration of sodium thiosulphate. This is because the difference in concentration doesn't prevent or affect the certain freedom of the particles in the liquid solution, unless they are compressed. I would expect my graph of rate of reaction against concentration of sodium thiosulphate to be proportional, it would resemble the graph below: Obtaining Evidence and Results Volume of Sodium Thiosulphate (ml) ...read more.

Conclusion

Pipettes would be very useful here. As in the experiment I used only two measuring cylinders, one for hydrochloric acid and one for sodium thiosulphate and water together, I had problems with the water and sodium thiosulphate as I quite so often passed the 10ml. fixed volume on the flask. Using pipettes would allow me to pour the liquids drop by drop when I need to and so makes it much harder to surpass the 10ml. fixed volume. Another way of fixing this problem would be to simply use syringes, they are very accurate in measuring the volume and they are easier to use. The best way to measure the volume would be to first take the solution with a syringe, then put it into the measuring cylinder and then add some more with a pipette. As I do not want the reaction to affect the experiment, I would want it to be constant. I cannot control the room temperature, unless there is air conditioning in the laboratory, but I could control the temperature of the solutions. The best way to do that would be to use a water bath. You would put the solutions in the water bath and you would keep the water at a constant temperature. Doing so is also easier, because if you used something like a Bunsen burner, it would be very dangerous especially when heating hydrochloric acid. Since I have problems with the timing of the reaction at low concentrations of sodium thiosulphate. Some sort of electronic device would help me to detect when the cross disappears completely. Perhaps something like a laser or a light bulb on top of the beaker and a receiver or a light sensor underneath the beaker would help. When the receiver shows that it doesn't receive any more or the least possible light, than the light could not go through the residue. Therefore if light or laser could go through, than I would not have seen it with my own eye. ...read more.

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