Making Agar cubes

Discussion in 'Supporting Biology' started by Vitreous Humour, Nov 5, 2019.

  1. Thats what we have done and seems to work well.

    I tried them before and I could never get them to come out right
  2. Depending on the teacher I either use ice cube trays (paint with veg oil first) or clean (not sterile) petri dishes (the pupils either use half or a quarter).
    I always use sodium carbonate solution and add everything but the phenolphtalein which I add when cooled sufficiently.
  3. We just did the ruddy BTEC. 15g agar (food grade or Nutrient) to a litre of boiled water, 10ml of 1mol NaOH to make it to 0.01m Concentration, lob in some phenolphthalein, chuck it in the microwave and reboil (or it won't set),pour,job done.

    12 repeats of that, you had my morning last week. However, not one failed. Used the last tray this week for a bunk filler prac on diffusion, so all gone now.
  4. Ours all faded over night. Any way to stop this happening next time?
  5. How long do you nuke it for?
  6. If they start going clear just drip some 0.1M NaOH over them - the colour will soon return so all is not lost
  7. I had to do this last year. I made the jelly up in metal dissection trays for 2cm, 1.5cm & 1cm cubes. Used petri dish & lid as described earlier for 0.5cm & 0.8cm. I covered it in clingfilm soaked in sodium carbonate to keep for several days. If the pinkness started to fade I squirted some sodium carbonate over the cubes just before the lesson and they pinked up really well. I found the smallest cubes faded very quickly once out in the air.
  8. Until it was bubbling again. Our microwave is an anaemic weenie...can't wait to it to pass to silicon heaven, I want a 950watt next time..