How does changing the Concentration of Sodium thiosulphate affect how fast it reacts with an acid?

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Fred        11NW – 111Y        Chemistry

How does changing the Concentration of Sodium thiosulphate affect how fast it reacts with an acid?

Introduction:

        The purpose of this investigation is to determine, how the rate of the reaction changes when sodium thiosulphate [Na2S2O3] is mixed with hydrochloric acid [HCl] at different concentration.

Prediction:

        The collision theory states that, the higher the concentration and if the volume of a solution stays constant; then the probability of collisions within the solution between particles will be higher than a lower concentrated solution with the same volume. The amount of particles in a concentrated solution will be greater so therefore, the probability of collisions occurring will be greater. In addition, the probability of successful collisions also increases proportionally if the concentration is increased at the same rate.

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Therefore, after considering collision theory involving the concentration of substances I can predict that the rate of the reaction between sodium thiosulphate [Na2S2O3] and hydrochloric acid [HCl] will increase proportionally as the concentration of sodium thiosulphate [Na2S2O3] increases. So, the higher the concentration, the shorter amount of time will be required for the cross to disappear. This happens because, the equation: Na2S2O3 + 2HCl » 2NaCl + SO2 + S + H2O, the sulphur causes the conical flask to become cloudy. However, there are other aspects involving collision theory like; temperature and catalysts, temperature is involved but is not being altered so therefore, will not alter the rate of the reaction, a catalyst is not being administrated so therefore, it will not assist in increasing the rate of the reaction. If temperature were being altered, temperature of the solution will affect the rate at which the solution reacts because, temperature gives particles more energy, therefore, the particles will move faster and they will then have a higher probability of colliding. In addition, because of the speed, there will be a higher number of collisions will be successful.

 Surface area, this is also an aspect of collision theory; we are dealing with two liquids which will be mixed together, not a liquid and a solid. If solids are broken up, you will get a larger surface area, which will be able to react with the liquid, more of the solid substance will react at one specific point in time. Subsequently, the rate of the reaction will increase, however that would not be true for a liquid. However reaction all depend upon one thing ‘Activation energy’, this is the amount of energy that is needed if the particles are going to react with each other. The faster the particles move, the greater the force of collisions will be, and the greater the energy will be too. Finally, I have decided that I will need three sets of results in order to create an average, which will allow me to create a good graph that will clearly show if my prediction is true. In addition, I decided to use certain volumes of liquids because; preliminary research into other similar experiments that were done helped me to determine this. [Information obtained from ‘http://www.danyey.co.uk/sci2.html’]

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Variables:

  1. The ratio of sodium thiosulphate [Na2S2O3] to water. Depending upon this ratio will depend upon the concentration of sodium thiosulphate [Na2S2O3] and therefore, will change the probability of particles colliding in the solution because; there will be more particles in one particular area. This should be the only variable that will change because; it is the variable that I am investigating and therefore the test will be fair if I change it.
  2. Changing the molarity of hydrochloric acid [HCl] and the volume of hydrochloric acid [HCl] must not be changed because; the ...

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