Reduction of copper oxide

Reduction of copper oxide


This experiment enables us to find the formula of copper oxide by reducing it in a stream of hydrogen.
The hydrogen removes the oxygen and forms water, which will be steam at
the temperature of the experiment. This is the apparatus we use. A pyrex reduction tube, which is
essentially a boiling tube, with a small hole in the end to
allow excess hydrogen to escape. Before starting the experiment it’s
important to familiarise yourself with how to use a hydrogen cylinder. This valve here, the cylinder valve, is
operated by a spanner. Turning the spanner allows hydrogen gas into the pressure reduction valve gear here. This valve is the pressure reduction valve, turn it on and we’ll see a reading on that gauge there, and finally the flow rate of the hydrogen is
regulated using this needle valve here. We first need to weigh the empty reduction tube. The balance used must read to at least two decimal places. We now place about three grams of copper oxide, which is really a couple of spatula-fulls of the powder, into the reduction tube. Try to place this in the centre of the tube. If it’s too close to the hole end there’s a risk of the hydrogen flow blowing some of it out. If it’s too close to this end, then there’s a
risk of heating the bung while we heat the copper oxide. Having put the copper oxide into the tube we re-weigh it. The copper oxide should be dry. Old stock may need to be dried in an oven or desiccator. We now use the needle valve to adjust the flow of hydrogen, a rate of flow that you can just feel on your cheek is about right. Now place the hydrogen delivery tube in the end of the reduction tube. The next step is to light the hydrogen but
it’s important to wait for about a minute to make sure all the
hydrogen has flushed out any air from the reduction tube
otherwise you could get an explosive mixture in there. For the
lighting process we have safety screens to protect the
demonstrator and the audience. Once something like a minute has passed we now light the hydrogen and adjust the flame until it’s about 2 cm or so. At this point there’s no more explosion
risk so we can dispense with the safety screens. Now we heat the copper oxide using a roaring Bunsen flame and using the hottest part of the flame,
which is just beyond the blue colour. At this point, a number of interesting observations can be made. These will probably need to be pointed out to the audience. Droplets of water will condense on the
cooler part of the reduction tube near the hole. These will evaporate as the tube gets hotter. The height of the flame will drop as some of the hydrogen is used up reacting with the oxygen in the copper
oxide. The flame may develop a green coloration caused by copper atoms vapourised into the flame. Use the Bunsen burner to chase the glow along the length of the oxide until all the black copper oxide has
been changed to pinkish copper. This will take up to a minute. When
no trace of black remains continue to heat for at least a further
minute to ensure that all the oxide on the inside of the heap has reacted. If in any doubt continue heating for longer. Make sure any condensation has
evaporated. When you’re confident that all the copper oxide has been reduced, the flame is back to its original height,
you can stop heating. It’s now important to leave the apparatus
exactly as it is with the hydrogen flowing. This is to prevent air from diffusing
back into the reduction tube and converting some of the hot copper back to the oxide. Continue until the tube is cool enough
to touch comfortably. You now blow out the flame, move the hydrogen delivery tube and turn off at the cylinder and re-weigh the tube, which now contains copper. The copper looks pinkish and not
particularly metallic. If students are not convinced that it
actually is metallic copper it’s possible to get some of it out of the tube and use a circuit tester to show that it is in fact metallic. Finally, we have to turn off the hydrogen
cylinder. We first close the cylinder valve with a spanner and we then need to use the pressure reduction valve. We turn it on, and the needle valve on to vent any hydrogen from the valve gear. Finally, turn off the pressure reduction
valve and also the needle valve.

21 Comments

  1. One very important thing to remember when dealing with pressure regulators on tanks like these…. NEVER stand in front of the adjusting screw when opening the main valve.

    Many have torn the threads out and shot the end off like a rocket… If you're standing there looking at it, you'll catch it with your face. Not good.

    Ask any professional welder for verification.

    Good video though!

  2. "this valve is the pressure reduction valve" That is a regulator, the main valve regulates the output pressure., If you intend to use any form of flow restriction. A flowmeter should be installed onto the manifold. (when dealing high pressure cylinders such as hydrogen, a double regulator manifold should be used)

  3. what type of glass text tube you uesd in this experiment ?
    is it borosil glass test tube or qurtz glass test tube ?
    as i knowns brosil glass with stand upto 450°C only.
    melting point of copper oxide is  1,326 °C

  4. Is it possible to use reaction between metal and hydrochloric acid to produce hydrogen gas instead of using hydrogen gas tank. If possible, is it hard to carry out the activity?

  5. Doesn't look anything like the sheets of copper I can buy from B&Q – looks more like the dust I get out of my vacuum cleaner.

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