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An investigation into how the concentration of sodium thiosulphate solution affects the rate of its reaction with hydrochloric acid.

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Sam Miranda S5A An investigation into how the concentration of sodium thiosulphate solution affects the rate of its reaction with hydrochloric acid. Aim; The aim of this investigation is to see how the concentrations of reactants effect the rate at which a reaction occurs. The reaction between Sodium Thiosulphate and hydrochloric acid can be used to investigate how the concentration of reactants used can effect the rate at which a reaction occurs. When the two chemicals react, they form a yellow precipitate turning a transparent solution into an opaque one. By using a beaker with a marked piece of paper positioned underneath it we can react the two chemicals of different concentrations and time the duration of the reaction. The pattern (in this case a cross) will disappear after a specific quantity of Sulphur suspension has formed. A chemical reaction occurs when two-reactant particles collide with sufficient energy, facing each other in the correct direction. There is always a transfer of energy and a new product formed. There is some times a change in the appearance of the new product. Adjusting several factors can increase the rate of a reaction. These include; - Concentration If we consider a reaction occurring in a solution the greater the concentration is the greater number of reactant particles are present or available. Therefore increasing the concentration will increase the rate of the reaction. The speed of the reaction is directly proportional to the concentration of the solution. This means, if the concentration is doubled them rate of the reaction will double. ...read more.


Factors to control 1) To ensure that reliable results are gained form this experiment there are a number of factors which need to be controlled, these include: 2) Only changing the concentration of the reactant to the required measurements there for I will need to. 3) Keep the temperature of the substances the same. Changing the temperature could effect the rate at which the reaction occurs. Increasing the temperature increases the kinetic energy the molecules have, therefor increasing the chance of collisions between the particles. Decreasing the temperature would have the opposite effect. 4) The volume of the container needs to be kept the same. Increasing or decreasing would effect the rate at which the particles collide and react with each other. This is because the change in the volume of the container results in a change of the area the particles have to move. 5) Use the same marked piece of paper, which is positioned under the beaker because the shading of the cross may effect the rate at which it disappears. Darker crosses may be a lot easier to see through the solution than lighter shaded ones. 6) For each concentration, I will need to take the results three times and get an average of the time taken (in seconds) for the cross to disappear. This will give me more reliable results. Conical flasks will be rinsed thoroughly before being reused, which we will do as there are limited conical flasks within the laboratory. Finally, we kept constant the person who watched the solution to see when they could no longer see the cross. ...read more.


I would have used a Bunsen burner, a water bath and ice to get the temperatures. I think that if I had done this experiment then the higher the temperature then the faster the reaction would take place. I feel this would happen as the particles would have more energy and move around more, causing more collisions, therefore the reaction takes place faster. The accuracy could be improved in a several ways. Wider containers would mean that the amount of solution would be 'thinner', and so it would take a considerable amount of precipitate until the cross was no longer visible, and vice versa. Therefore it is important that the width of the conical flask is maintained. Another way would be to change the method of the experiment completely. A light probe and data logger attached to a computer will give more accurate results than the human eye it would replace. It would act not only as an eye, but also a stop clock, measuring until there is zero light intensity getting through the solution. The downside to this method, however, is that the temperature of the bulb will eventually heat up the solution, and speed up the reaction If I conducted the test again I would perform several repeats for each concentration, making the results more reliable. I would consider changing the concentration of the Hydrochloric acid and react it with Sodium Thiosulphate Solution, as it would be intriguing to see if the results were the same. I could use similar concentrations but at higher temperatures, and add this information on to the graph that I had already drawn in order to see any contrasts. Further experiments could involve the usage of other reactants and possibly catalysts. ...read more.

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