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The Determination of an Equilibrium Constant.

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The Determination of an Equilibrium Constant – Skill E

        During our experiment, it became clear that there were a variety of errors due to procedure that has culminated in anomalous results producing an inaccurate Kc value.  There are two main sources of inaccuracies; systematic errors and equipment errors.  The main sources of systematic errors were:

  1. The amount of phenolphthalein added to the solutions
  2. The difficulty in judging the exact point of colour change from colourless to pink during the titration.
  3. The difference in judging where the bottom of the meniscus is.

The systematic errors are non-quantitative; therefore it is impossible to predict the effect of the errors mathematically.  But, due to the repetition of the titration, we are increasing the precision of our results, thereby decreasing the event of an error being produced.

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.Minor inaccuracy from the 100cm3 standardizing flask.

As the results of the experimental errors produced quantitative errors, it is possible to work out the results in account with the percentage of errors due to the equipment.  The calculation has been shown on the analysis sheet.  The error due to the burette was (0.05/16.8) x 100 = 0.3%, and the error due to the pipette was (0.1/1) x 100 = 10%.  Therefore, the total error due to equipment was 10.3%, ignoring the inaccuracy due to the standardizing flask as it is so small it can be ignored.

        Another large source have error cannot have been foreseen.  We based our experiment on the fact that the solutions we were given were in equilibrium, but we cannot be sure that this is true.  Although

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Ways to improve the experiment

  • Increase the time for the solution to reach equilibrium
  • If we could increase the quantity of HCL in the solution, this would increase the speed at which it takes to reach equilibrium
  • By repeating the experiment and taking an average, the precision of the experiment will be increased
  • As we know, the only factor that effect the Kc, is the temperature, so by repeating the experiment on different days, the difference in temperatures will be accounted in our value  
  • Increase the amount of the solution we pipette.  By doing this, we decrease the percentage error due to the pipette as if we take a larger volume; +/-0.1cm3 will decrease as a percentage of error.

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