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Rates of reaction - Sodium Thiosulphate + Hydrochloric Acid.

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Introduction

Sodium Thiosulphate + Hydrochloric Acid Plan I must produce a piece of coursework investigating the rates of reaction, and the effect different changes have on them. The rate of reaction is the rate of loss of a reactant during a chemical reaction There are five factors which affect the rate of a reaction: * Temperature, * Concentration (of solution), * Pressure (in gases), * Surface area (of solid reactants), * Catalysts. I have chosen to investigate the effect of concentration on a reaction. This is because it is the most practical to investigate. The others are very difficult to get accurate readings due to human error. Similarly the use of a catalyst complicates things, and if used incorrectly could alter the outcome of the experiment. The aim of my experiment is to see the effects of a change in concentration on the rate of a reaction. The reaction that will be used is: Sodium Thiosulphate + Hydrochloric Acid Na2S2O3 (aq) + 2HCl (aq) Sodium Chloride + Water + Sulphur Dioxide + 2NaCl (aq) + H2O (l) + SO2 (g) + Sulphur S (s) Both the sodium thiosulphate and the Hydrochloric acid are soluble in water, so the concentration of either can be changed. However I have chosen to vary the Hydrochloric acid as it is available to me. ...read more.

Middle

This means that my graph drawn up in my analysis will have positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration is increased. This can be justified by If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself: For a reaction to occur particles have to collide with each other. 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, or Ea. 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. Concentration - If the concentration of a solution is increased there are more reactant particles per unit volume. ...read more.

Conclusion

The rate of reaction was quicker when there was a higher concentration of sodium thiosulphate. This can easily be seen when we look at the results table. This may have also have been the same if I had used the Sodium Thiosulpahte as a variable instead of the hydrochloric acid . It may have been faster or slower at reacting than the hydrochloric acid. This is the only anomalous result that I have recorded. The result may have turned out anomalous because of basic human error, or maybe because we measured the substances wrong. It may have even been because we did not clean the apparatus properly. Apart from this, the accuracy of my experiment has been more or less accurate. Although there are a number of ways in which we could have made the results more reliable. For instance, we could have used better measuring equipment, because the apparatus we used was mainly basic equipment. Another thing we could have done to bring more evidence is to have tried to use the hydrochloric acid as the variable substance, and used the sodium thiosulphate as the constant substance. This would have brought more evidence to support the idea that the higher concentration of a substance, the faster it will react. I think that the evidence, which I have received, is enough to reach a suitable conclusion, but there are a few flaws to the experiment (which I have mentioned). Apart from them, the experiment is fine. ...read more.

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