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AQA precipitation ISA

Discussion in 'Science' started by found nemo, Jun 29, 2010.

  1. No idea. I took one look at it and decided I wouldn't be doing this one! About as practical to do as the unsaturated oils one (remember? 30 students + one fume cupboard). The C1 ISA from this set looks equally as dismal (something to do with carbonate + acid then measuring depth of foam produced after adding washing up liquid!!!!!!!!!!!!)
     
  2. blazer

    blazer Star commenter

    Blimey, you have a fume cupboard! We just open a window!
     
  3. Window? We dream of a window. We just let the fumes drift out of the hole in the roof![​IMG]
     
  4. blazer

    blazer Star commenter

    You have a roof!!![​IMG]
     
  5. Well, we call it a roof. It is actually a lump of soggy cardboard held together by spit and the discarded feathers of a Norwegian Blue Parrot that happened to be sort of flying by.
     
  6. phlogiston

    phlogiston Star commenter

    What is the reaction in the ISA?
    P
     
  7. blazer

    blazer Star commenter

    Barium sulphate and a chloride IIRC
     
  8. Barium chloride and sodium sulphate.
     
  9. blazer

    blazer Star commenter

    Thats the one! Anyway our techie is doing her head in trying to get a differentiated result using the recommended concentrations. We tried Zinc Sulphate, sodium carbonate as an alternative but the precipitate will not settle in any reasonable time. We tried flocculating with aluminium salts with a litte success but still too fiddly to be of any use in a classroom. Who thinks of these ISAs and why don't they trial them before sending themout to us?
     
  10. I'm sticking with 'Energy Changes' for C2 as it's still live! Got some good results with 1M copper sulphate and changing the mass of zinc used.

     
  11. The Energy Changes one gives a good practical, but has some obscure questions that make lots of pupils lose 4 marks at least - that's a whole grade. We are not happy with the paper.
     
  12. phlogiston

    phlogiston Star commenter

    Barium chloride used to be a standard qualitative test for sulphate ions. I would have thought it needed to be fairly concentrated (>0.5M). I would be concerned about it's toxicity. (about a third as toxic as cyanide as I recall). If it stays in the test tube and they wash their hands afterwards it should be OK, but definitely needs a risk assessment.
    My Dad had barium sulphate somewhere very rude!
    Best wishes,
    P
     
  13. I'm doing it now and I decided to use KI and PbNO3. It gives beautiful yellow precipitate and quite a good height in the test tube. we don't have enough balances so I'm measuring the height of the ppt. It settles in a shorter time, so they can do the practical let's say today and measure the height of the ppt tomorrow.

    I hope this helps [​IMG]
     
  14. Going back to the C1 ISA we changed the reaction slightly - the teachers notes mention measuring temperature as a readout so we subsituted the carbonate for Mg powder.

    Our metal ores were mixtures of Mg and acid washed sand, add a fixed amount of HCl and measure temperature change after 2 minutes. Worked like a dream.

    Agree with the complaint about testing - The P1 ISA took me a week to get working and I think energy changes is about the only chemistry one that ever worked without major tweaking. But as was mentioned it has about 4 marks that are almost impossible. This year we did crumple zones first - that got about 75% above a C, then did energy changes, got us to about 90% (although most did worse than in crumple zones), now just going to do either precipitates or enzymes with the remaining few that are below about (predicted) 65 UMS.
     
  15. I'm about to attempt the Metal Ores ISA. This method looks like the most foolproof! Can I ask what kind of proportions of Mg and sand you used? Stupid question: do I buy acid washed sand or acid-wash my own? Also, does the Mg separate out from the sand as it is more dense? Huge thanks - you could save me precious time faffing in our prep room this week.
     
  16. Sorry only just saw reply. A tried a range of ratios but about 1 part Mg to 5 parts sand worked best - 1 spatula or so per test.

    We used commercial acid washed but thats just what was to hand. Can't see why you couldn't wash it yourself.

    Mg didn't separate too much unless really shaken around. This would probably depend on the courseness of your Mg powder though
     
  17. Ah well - at least its not the flipping oils one.

    Doing that with some kids this week... Glycerol works pretty well Much better than oil anyhow!
     
  18. ScienceGuy

    ScienceGuy Occasional commenter

    We use diluted PVA with cups of different size holes and it works a treat, particularly as we use small, medium and large as the values for hole size
     
  19. Agree with washing up liquid, only I do different temperatures (ice bath, room temperature, 30 and 40 degrees) and get some good results.
     
  20. blazer

    blazer Star commenter

    Don't you have to do at least 5 values of the independent variable?
     

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