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21C science chemistry errors - candle in a jar

Discussion in 'Science' started by TeasMad, Jan 27, 2012.

  1. TeasMad

    TeasMad New commenter

    Last week I read in OCR's 'new' scheme of work for mod C5 of 21C science
    "Demonstrate that approximately one fifth of the air is oxygen by using a burning candle on a watch glass/petri dish in a trough of water. Place an upturned beaker over the top of the candle. When the candle goes out it has used up the oxygen and the water will rise up the beaker to replace the used gas. The percentage the water has moved up the beaker is approximately equivalent to the amount of oxygen in the air."
    I was vaguely horrified (if not exactly surprised!) to read this rubbish, and emailed OCR to that effect - they have yet to reply.
    Anyone had any previous success correcting stuff published by exam boards? Perhaps more adverse publicity is only way to get an improved version... hence posting here to see what others think
    About the most comprehensive (correct) information I could find online is an article by H Dhindsa - Googling 'Dhindsa candle burning' should find it.
    I also found what I thought was a rather better lesson plan then OCR's at

  2. lunarita

    lunarita Lead commenter

    I also hate this experiemt, though have only seen it at KS3, not GCSE.
    In fact, I remember first seeing it as a trainee and thinking 'wow, how clever' until I started to think about it and work out numbers of moles and stuff.
    I knowit's a very good visual thing but it's all wrong and I can't bring myself to do it.
  3. mm38

    mm38 New commenter

    Surely you'd be much better off doing the heating copper between two gas syringes experiment if you want to know how much oxygen is in the air?
  4. phlogiston

    phlogiston Star commenter

    An experiment in 21st century?
    Ah, only a demo,and a wrong one. This was supposed to be the jewel in the crown of modern science education - and it's so badly structured - and boring.
    Then last year OCR were giving grade A to candidates who got half the C456 paper wrong followed by us wondering why our A level students struggled so much. 21st century has really put me off my job.
  5. TeasMad

    TeasMad New commenter

    Sadly the deathly silence from OCR remains unbroken. Has been over a fortnight now. Will let you know if they ever reply, but I'm not holding my breath.
    Still, my own kids - KS1 age - had a lot of fun the other day in the kitchen demonstrating that we could easily displace 38% of the air from a large coffee jar using 4 small birthday cake candles (that's some impressive 'oxygen consumption!'). 1 candle displaced 17%, for reference.
  6. TeasMad

    TeasMad New commenter

    or maybe we woz just using the wrong sort of candle. Kind of like the
    wrong sort of snow (but not much). Must check the small print, possibly
    they were value basics candles which can run on nitrogen when the
    oxygen gets a bit short. Maybe I'll ask OCR what they think, I'm sure
    they'll know.

  7. I think a letter to The Times - copied to OFQUAL, TES, The guardian, Daily Mail, Michael Gove ..... is needed to highlight the level of academic rigour that exists in the exam board which is being trusted to direct, develop and examine the population's academic potential
  8. blazer

    blazer Star commenter

    Be careful, it is probably the awarding body that gave Gove his qualifications!
  9. TeasMad

    TeasMad New commenter

    Result! - OCR replaced the scheme of work with an updated version today. Presumably the message eventually reached the appropriate person. Definitely better late than never.


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