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Testing for unsaturation

Discussion in 'Science' started by gasheadruss, Aug 5, 2011.

  1. Hi all,
    I am making a few changes to my lessons after completing my first year and wanted to do a practical testing alkanes/enes for unsaturation.
    I've done this as a quick demo before but would like to get the pupils doing it for themselves but I'm seeing mixed opinions on this from a H&S point of view when I search for it online.
    We have access to 1 fume cupboard in my lab. Is a practical where they would be using bromine water and a selection of alkanes/enes (pentane, hexane, hexene, cyclohexene) advisable? Would pupils have to collect all liquids from the fume cupboard and keep bungs on test tubes at all times that that they were away from the cupboard?
    I'd appreciate any advice on how others play this practical.
    Thank in advance
     
  2. Hi all,
    I am making a few changes to my lessons after completing my first year and wanted to do a practical testing alkanes/enes for unsaturation.
    I've done this as a quick demo before but would like to get the pupils doing it for themselves but I'm seeing mixed opinions on this from a H&S point of view when I search for it online.
    We have access to 1 fume cupboard in my lab. Is a practical where they would be using bromine water and a selection of alkanes/enes (pentane, hexane, hexene, cyclohexene) advisable? Would pupils have to collect all liquids from the fume cupboard and keep bungs on test tubes at all times that that they were away from the cupboard?
    I'd appreciate any advice on how others play this practical.
    Thank in advance
     
  3. sci84

    sci84 New commenter

    See CLEAPSS leaflet PS 67-01 Testing for unsaturation
     
  4. I was hauled over the coals once for this... not because of the smell of bromine but rather the cyclohexene!
     
  5. phlogiston

    phlogiston Star commenter

    Water companies don't like halogenoalkanes down the sink. They kill the bacteria at the sewage plant. Although in fact, as they are denser than water, you usually find them when you have to empty the sink traps.
    P
     
  6. Don't you think that in the amounts that schools would be disposing of i.e less than 50ml per lesson probably, the dilution at the treatment plant would make this negligible?
     
  7. Mangleworzle

    Mangleworzle Star commenter

    I do the cracking of paraffin practical and collection of ethene over water. The kids then bring to me their tubes of gas stoppered with a rubber bung which I then test with bromine while they stand there. If they get it (i.e they've made ethene successfully) their names go on a list on the board. Not sure if this is what you want but it works for me, otherwise it's just a list of chemicals and it happens or not which I find is a bit hit and miss in terms of understanding what's going on.
     
  8. phlogiston

    phlogiston Star commenter

    Probably, especially as I suspect most of them will either get stuck in S bends, or evaporate.
    Important to remember that you do really only need a drop or two of the hydrocarbons - and that you must not let the dissolving of the bromine in the hydrocarbon layer distract you with alkanes.
    P
     

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