Factors affecting the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

Results

Conclusion

As we can see in the table of results, the highest concentration is 0.2mol and this took only 30 seconds in which to obscure the cross beneath.  When you look at the last row of the table you can see that 0.0125mol of the solution took 9 minutes to react.  This clearly shows that when the concentration is greater, an experiment occurs quicker.  As the concentration was halved the time taken for it to completely react doubled.  As we can see it took 30 seconds for 0.2mol to react and it took 1 minute for 0.1mol to react.  The time continues to double as the concentrations are halved.  In the results we can see that as the concentration of the solution decreases the time taken for the reaction increases.  The times for the reactions increase proportionally as the concentration decreases.  The Rate of Reaction varies greatly. Some chemical

reactions like explosions happen very quickly while others like rusting take time and happen very slowly. The rate of reaction can

be affected by a number of factors: temperature, concentration,  pressure, adding a catalyst and surface area . The one that I have investigated is Concentration.  The factors that affect the rate of a reaction are called the collision theory.  When the concentration is higher there are more particles so the number of successful collisions increases.  The minimum energy needed for a successful collision is called the activation energy. For a reaction to take place molecules must collide with each other. When they do they must have enough energy to start a reaction. The level of energy needed to start a reaction is called its energy barrier.  So in order to break the energy barrier, there has to be enough activation energy so the reaction will take place. The increase in concentration helps to speed up the reaction as increasing the concentration of the solution increases the number of particles therefore increasing the number of collisions. If the concentration is increased, the average number of particles is increased.  This also means that there is a greater number of particles with enough activation energy.  The Collision Theory states that: To react particles must collide with enough energy to break existing bonds and bring reactive sites closer together. Bringing the reactive sites closer together means that the chance of a reaction occurring is increased.  My prediction is supported by the results as the results prove that as the concentration decreases the time taken for the reaction increases. In the table you can see that for the smaller concentrations of Sodium Thiosulphate, which was mixed with distilled water the molecules were less dense and so the activation energy was not reached as quickly.  As there was less energy the time for the reaction to occur increased.

Evaluation 

I think that this experiment has been completed successfully. My results were accurate as each measurement was checked carefully.  There were no anomalous results within my results table and I think this was because of the extreme care that I put into
making sure that the experiment was set up correctly with careful measuring. I feel that I should have repeated my results to make sure that the results that I obtained were not incorrect.
In the table you can see that for the smaller concentrations of Sodium Thiosulphate, which was mixed with distilled water the molecules were less dense and so the activation energy was not reached as quickly.  As there was less energy the time for the reaction to occur increased.

Overall, this investigation has been a very successful one. I feel my results and analysis have been as precise and reliable as they could have been under the time given. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables for example Temperature or adding a catalyst.  This would have furthered my investigation.