Percentage errors!??? question

Discussion in 'A-Levels' started by Tamxxx, Apr 22, 2007.

  1. Tamxxx

    Tamxxx New Member

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    Im in my evaluating part, and i have to include % errors, the thing is I only have one % error in my titration experiment and my teacher said that you have to include percentage errors for all measurements, The thing is how can if i didnt have any errors?:confused: :confused:

    Shall i just make it up?

    Will I lose Marks if i dont have any % errors?
     
  2. hash118118

    hash118118 New Member

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    What do you mean you didn't have any errors? I don't think you understand the concept of percentage errors - you are analysing the errors assosciated with the appartus you have used - these errors are beyond your control. Don't say that you foolishly added too much of a chemical or something cos that will lose you implementation marks. For a titration, you will need to include % errors for balances used to measure the mass of any solids, any volumetric flasks you would have used to prepare standard solutions, pipettes for measuring your analyte solution and burettes for measuring the volume of titrate used.
     
    #2 hash118118, Apr 22, 2007
    Last edited: Apr 22, 2007
  3. Tamxxx

    Tamxxx New Member

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    Thank you for replying. Yeah I think i thought the wrong thing lol now im totally confused about this whole percentage error in my titration =(

    I used

    250cm3 Volumetric Flask

    Electronic Weighing scale

    250cm3 Conical flask

    Pipette

    How do i find the % errors for these equipment? like what are the numbers for equipment?:confused:
     
    #3 Tamxxx, Apr 22, 2007
    Last edited: Apr 22, 2007
  4. izz_1616

    izz_1616 New Member

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    we did this exact same coursework!! our teacher said that the titration is the most accurate, and you really cant make that many changes. i dunno about the percentage error thing, she said something about 0.1%, but dunno if that was for the heating method or for the titration. thats prob not much of a help but thats all i remeber about it!! sorry!
     
  5. hash118118

    hash118118 New Member

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    I hope you didn't measure anything using a conical flask! There is a graduation mark on the conical flask just to give you a rough idea of how much of the stuff there is.

    For the electronic weighing scale, assuming it reads to 2dp, then the error would be ±0.005. Knowing how much you weighed, you should be able to work out the % error.

    As for the others, i think it says the error on the actual piece of apparatus - this you may have to look up.
     
  6. Virus_Tamer

    Virus_Tamer New Member

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    % error =
    Degree of error
    ----------------- x 100
    Your measurement

    On a burette, the degree of error is usually about 0.05 cm3 (although you should be given this figure), so if your titration figure was 20.05 cm3, the % error would be:

    % error =
    0.05
    --------- x 100 = 0.249%
    20.05

    Hope this helps!

    M
     
  7. Tamxxx

    Tamxxx New Member

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    Thank you everyone for answering me it has helped me alot:) :) and i have used some of your information in my % errors. This is what i have done


    I used mostly volumetric equipments. here is example

    Burette

    0.05
    ---------- X 100 = 0.212 % error
    23.6 ( this is my average titre result)

    And i did the same thing will other equipment, the average titre was on the bottom, i did the same thing for volumetric flask:confused: is this correct or do i put something else on the bottom?
     
  8. abbie

    abbie New Member

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    Don't forget that for everything you weighed there are two % errors. One for setting the scales to zero and one for the actual reading. If ur using a 2 dp balance, the error is 0.005*2=0.01 g
     
  9. hash118118

    hash118118 New Member

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    Oh. Never thought of that - very clever. LOL that means i've done my AS and A2 chemistry cw wrong. Oh well.
     
  10. Pammy

    Pammy New Member

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    Sorry this is a very late reply to this post, but I just came across it and would like to comment: I don't think that you should take the two errors. If there is a zeroing error, it is most likely a systematic error. It will only be wrong if there is something wrong with the scale already. It is not a measurement. When you set the scale to zero, you determine that this point is zero, and that's that - there's no measurement error in that...If you make several measurements all compared to the same zero value, whether that value is inherently right or wrong becomes irrelevant, but it will be the same for all measurements. This is to say: it only affects accuracy, not precision. And when you're measuring %age errors, you are talking about precision!
    Imagine a simple dial bathroom scale, then it may become clearer.

    Pammy
     
  11. GreenSherbet

    GreenSherbet New Member

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    does anyone know the accuracy and pecentage error of a digital stopwatch??
     
  12. alvo23k

    alvo23k New Member

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    the way we learnt it was to take half the smallest reading and that is the absolute uncertainty. So if it is to 2 decimal places the absolute uncertainy is ± 0.005 units. if u divide this by the result you get the precentage uncertainty/error.

    But that works best for stuff like mass and length. Time is something where you have to take into account your reaction time...i think the best uncertainty for time is about ± 0.5s because thats how long it takes to react..
     

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