Convection currents using potassium permanganate

Discussion in 'Supporting Physics' started by Carol Taylor, Dec 6, 2018.

  1. Carol Taylor

    Carol Taylor Footsore

    How do you peeps give out class sets of pot.perm so that the kids can still drop a few grains to the bottom of a beaker of water? I used to use pots wide enough for the tweezers to access the grains and drop them down a glass tube.
  2. Teacher demo. 2l beaker on tripod. Few grains pot perm to side of beaker and heat area lightly with bunsen.
  3. Either a teacher demo with the convection tube or if they insist on the class doing it the teacher is given a single pot and tweezers to distribute to them one at a time after they've set up
  4. When the students do this (not often, usually teacher demo) I give out little screw top test tubes with a grain or 2 in each, with a glass tube, to use in 100 or 250ml beaker. Takes a bit of prep time, but saves them putting a whole spatula in, even after they've been told not to.
  5. another method is to freeze ice cubes of coloured water. the kids can then put an ice cube into a large beaker and heat.
  6. Carol Taylor

    Carol Taylor Footsore

    I offered this version. HOD thinks it's great and always does that now, chemistry teacher who wants this for physics lesson turned down my suggestion of coloured ice even though it leaves a lovely coloured trail heading to the bottom of the beakers.
  7. Carol Taylor

    Carol Taylor Footsore

    If only. She has a liking for class experiments.
  8. same method as Al F but we use spirit burners as its gentler and slower
  9. I put a few grains into a specimen tube.
  10. we use tea lights
  11. I only ever give them a teacher demo - your options are convection tube or big beaker!
  12. Stan the Skeleton

    Stan the Skeleton Registered Supplier

    A bone of contention for me was when students struggled to use a "few" crystals. To get around this, I used to give them forceps and small balls of plasticine rolled in pot perm. This worked well for both convection and diffusion experiments and reduced the amount of chemicals being used.
  13. Great idea.
    We do a teacher demo too unfortunately.
    This method works nicely though, in case anyone else hasn't seen it. I nicked the idea off the youtubes somewhere.

    convection demo (hot potassium permanganate and ice).jpg
    Hot water in the flask, cold/room temp water in the tank and then drop in ice cubes (top left of picture) once a decent layer of pot.perm has built up.
    AllantheTech likes this.
  14. I stole the same one off youtube. I use food colouring to save on time disposing of it though

  15. These two methods

    Somewhere (cleapss?) there is a way of making a waxy ball thing with potassium permanganate that will control the amount they use if the teacher doesn't want to hand it out themselves
  16. teacher has a pot and tweezers and goes round the class dispensing it safely.
  17. The potassium permanganate we have is the powered stuff rather than crystals, I have had one teacher complain about this for years. I am in no rush to get a hold of crystals when rubbing small pieces of blutac in the power works just as well. I have a feeling the powder will out last me.
    Tony Worthy likes this.
  18. we make our own crystals, but they are quite needle like and difficult to get a decent size. We use the convection tube as a demo. Another demo with a gar jar of tap water and a coloured ice cube. The class experiment is making paper convection spirals.
  19. 1g of magnesium nitrate , melted in test tube , add 1 crystal of Potassium permanganate. pour the melt onto cold aluminium sheet.
    allow to cool and then cut up into squares of about 3mm . or use the whole thing if doing as a demo
    these can then be used as crystals and take awhile to diffuse so you don't need to drop down a tube ,
    Carol Taylor likes this.
  20. very rarely - this is usually a teacher demo. For classes, I have old contact lens pots that I place a few grains in for each group of pupils. Or some teachers prefer me to give them one pot and they share it out.