estimating the size of a molecule using an oil film

Discussion in 'Supporting Physics' started by Smiff12, Nov 8, 2018.

  1. Hi Does anyone have any straightforward instructions for this practical please? I've got some from the Institute of Physics but it seems very complex and long winded :( Just wondered if anyone has done this before and has a simpler version. Many thanks.
  2. :confused: I ought to know how to do this as my masters is in surface science and I know this was one of the practicals we did. In my defence I graduated 20+years ago.

    It's not something we do here
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  3. I think we've done it in the dim and distant past but I can't find any reference to it in my own files
  4. I seem to think there was a simple version but that's probably just wishful thinking :D
  5. We did this at school. You need to get the diameter of the drop and the diameter of the oil film on the surface of the water. We used lycodium powder on the water surface and a travelling microscope for the measurements as I recall.
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  6. lycopodium powder sprinkled on top of the water & a VERY small drop of oil - do it in a standard gratnell tray (which gets pretty messy with the powder & oil stuck everywhere)
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  7. We did it in waxed baking trays..... probably from before Gratnells existed or plastic was discovered :)
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  8. Ahh that's why is suggests wax :D It also mentions vegetable black!!! Any suggestion on that one gratefully received :D
  9. wood charcoal
  10. Vegetable black is literally a black pigment made by burning veg oil
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  11. Thanks!
  12. use the wax in the dissection trays in Biology
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  13. hbc


    We have just done this using the Institute of Physics instructions but just using old enamel tins not black waxed and using a microscope scale borrowed from biology and binocular microscope not perfect but good enough to give an idea of the procedure and results in the right ball park. Gave lots of opportunities to discus how the method could be improved
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