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Sodium Thiosulphate Reaction Rates

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Sodium Thiosulphate Reaction Plan This investigation is about rates of reaction and what affects them. In my experiment I am going to look at hydrochloric acid and sodium thiosulphate which is a precipitation reaction. They react together as shown in the equations below: Sodium thiosulphate + hydrochloric acid --> sodium chloride + sulphur + sulphur dioxide + water Na2S2O3(aq) + 2HCl(aq) --> 2NaCl(aq) + S(s) + SO2(g) + H2O(l) A reaction occurs when particles of the reactants meet and combine; this is called the collision theory. To increase the rate of reaction it is necessary to cause more particles to collide harder/at more speed and make it happen more often. There are several ways to do this and these make up the variables for this experiment. Two examples of reactions are Rusting and a bomb exploding. Rusting is an example of a very slow chemical reaction between Oxygen and (a liquid) most commonly Water on Iron, this results in a substance called Iron Oxide being formed. A Firework is an example of a very fast reaction, the fuse is lit and then the gunpowder ignites causing an instantaneous explosion. To ensure that I make the experiment a fair test I will have to ensure that I use: - * The same person to time the experiment. * The same person to watch the cross. * The same type of measuring cylinders (25cm?) ...read more.


I will then repeat the experiment again for the remaining temperatures. Test Range: - 25?c, 30?c, 35?c, 40?c, 45?c, 50?c and 55?c. [I found that starting with the highest temperature and working my way down to the lowest temperature was more efficient as it meant I only had to heat the water once] Fair Test: - To ensure my results are accurate I will use the same person each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the Hydrochloric Acid and Thiosulphate will not be mixed up. The amount of Hydrochloric Acid will be 5cm3 each time, and the amount of Sodium Thiosulphate will be 50cm3 each time. All of these precautions will make my final results more reliable and keep anomalies at a minimum. Key Factors Factors that will affect my experiment include: - * Concentration of the Hydrochloric Acid & Sodium Thiosulphate as these are both soluble in water. * Temperature of the Acid and Sodium Thiosulphate. * The use of a catalyst to increase the rate of reaction. * The use of different containers in which to hold the experiment as surface area affects the rate of reaction. * Increasing the pressure. All of these will affect the rate of reaction of my experiment. I will have to control the majority of these by ensuring that I ensure that my apparatus are dry and free of water. ...read more.


Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area. Preliminary Work Temperature Temperature (?c) Time Taken (Seconds) 21.5�c (Room Temp) 222.03 45�c 113.50 For the preliminary work testing temperature we used 5cm3 of Hydrochloric Acid and 50cm3 of Sodium Thiosulphate. Concentration Temperature (?c) Time Taken (Seconds) 21.5�c (Room Temp) 322.19 21.5�c (Room Temp) 231.34 For the preliminary work testing concentration we used: - 20cm3 of Hydrochloric Acid and 20cm3 of Sodium Thiosulphate for experiment 1 and 15cm3 of Hydrochloric Acid and 25cm3 of Sodium Thiosulphate for experiment 2. From My Preliminary Work I have found that both changing the concentration of the solutions and also altering the temperature of the solution both affect the time it takes for the reaction to occur and thus the rate of reaction. I will be performing the experiment altering the temperature of the acid, as this would be a hard variable to control. I will perform my main experiment in the same way that I have carried out my preliminary work. ...read more.

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