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Production of Pure, Dry Oxygen from Silver Oxide

  1. Aug 13, 2012 #1
    Hi everyone.

    I have been presented with a problem- to produce a set amount of pure, dry oxygen in any way I can, provided it is safe and accessible. I have chosen to tackle the problem by heating silver oxide until the silver and oxygen separate, however there remains the problem of isolating the gas, drying it and collecting it. I was going to displace the gas with distilled water and then somehow get the gas to go through a condensing tube filled with drierite to remove the water vapour (quick note: all this is done in vacuum sealed glassware) so I can collect it. However, gas is a bum to work with, because it wants to fill its entire container.

    I'm working with high school laboratory equipment, so I unfortunately can't supercool my oxygen. I was wondering if anyone here had any ideas. Also, if anyone sees anything wrong with my partial solution, please tell me before I embarrass myself and my chem teacher.

    Kind regards,
  2. jcsd
  3. Aug 25, 2012 #2
    Firstly, you are probably on an achievable track.

    How much is your "certain amount"? And would your equipment available stretch to:

    (1) a vacuum pump or vacuum line of some sort (but not a water pump), and
    (2) a round bottomed gas flask that will withstand a temperature of 300-400°C
    (3) a means of vacuum sealing this flask with a single exit nozzle and a vacuum tap


    If so, you can proceed as follows

    (1) make a calculation with the gas laws to find the right amount of sliver oxide to use. It must make a pressure of no more than 1 atmosphere of oxygen at 300°C if it all decomposes.

    (2) grind it gently if necessary in a mortar and pestle. Do not grind hard or you will lose oxygen from local frictional heating.

    (3) mix it with about double the quantity of quicklime -- calcium oxide -- to ensure that
    any water is well and truly removed from the system in the heating step later on.

    (4) add the mixed powders to the bottom of the flask, and vacuum seal it. Pump the air out of the flask and close the tap.

    (5) gently heat the flask from the outside until you can see that metallic flecks have replaced the black/brown material in the powder. This is best done in a fume hood with the sash pulled down to avoid danger if the flask should break. The temperature required is 300-400°C. You will probably have no way of reliably checking it

    (6) when the flask cools down, it should contain roughly half an atmosphere of oxygen, along with the solid material, but there is no need for separation. the oxygen is accessible through the tap, and can be drawn off

    These procedures come very close to the limit of what is acceptable on this forum; please show your intended procedure to your teacher/supervisor, and work under their direct supervision, and in their presence.

    -- Glass (pyrex or any other sort) vessels are not unlikely to shatter if their internal pressure differs much from 1 atmosphere.

    -- Both silver oxide and quicklime are powders that can cause significant burns if they get onto your skin.
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