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Thinking hard about errors in titration!

  1. Apr 7, 2005 #1
    hi guys assistance in this area would be great just see what i have written and comment on them please thanks! all.

    im thinking about the errors in titration from doing a typical acid-base titration to talk about in my experiment and these are the errors i came up with. First of all my class got a higher average titre required to titrate NaOH against citric acid so im thinking why my titre + concentration of citric acid is low. These are what i came up with.

    My experimental procedures were given 50ml of lemon juice, get 20ml into conical flask, dilute to 200ml with water, add ethanol near the end to get rid of bubbles, invert the solution 40 times. get 20ml aliquots from the dilute solution, titrate against NaOh and observe the end point turning to pink from the indicator.

    * citric acid liquid was lost to splashing before the end point was reached.
    * buret may have been contaminated with some other solution other than the one being tested.
    * reading of the buret may have been off.
    * distilled water remained in the buret before analysis
    * maybe did not get exact 20ml from the 50ml original

    My friends told me these notes below but i dont know what they mean someone care to explain:
    * bubble appeared during titration in the tip of the buret. " the buret contained NaOH so what bubbles are they talking about???/ what error is that?"
    * Titration nozzle was not flush with the mouth titration tube." no idea what they are talking here heh"

    So can some one read the experimental procedures and determine some errors / add to my existing one/ tell me if my errors are wrong :p and btw what does the inverting do????? and also how does it change ur results????? and lucky last question does adding too much ethanol do anything to the results thanks!
  2. jcsd
  3. Apr 7, 2005 #2
    You could always have my personal favourite: 'Substance X was not actually substance X'. But back to stuff you will want to use:

    I think these are when you are meant to run the burrette through with the substance to stop air bubbles making the experiment inaccurate.

    Others errors can include the funnel (if used) being left in the burrette causing inaccuracies in the measurement from the burrette.

    Hope this might help a bit.

    The Bob (2004 ©)
  4. Apr 7, 2005 #3
    Other possible errors would be sample contamination, since you mentioned that your results were a little low. Could there be something else present in your sample other than citric acid?

    The burette could be dirty, thus affecting volume measurements. Reading of burette should be to 2 decimal places approximation for higher accuracy. Burette should be washed thoroughly with distilled water and rinsed with the solvent you are going to fill the burette with to titrate. If there are droplets adhering onto the inner surface, it means that the burette is dirty.

    Air bubbles at the tip would affect the volume of NaOH read from the burette. E.g. with the air bubbles, would it still be 20ml you're reading or less?

    Was the stock sample well mixed before taking out 20ml aliquots?

    Hope this helps! :smile:
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