When students meet the reactivity series for the first time,
it might be fairly common for them to investigate some reactions of magnesium
or zinc and some other metals with hydrochloric acid for example, producing some hydrogen gas.
They may even have a go at reacting some calcium with some water, also producing some hydrogen gas,
and have demonstrated to them the reactions of the alkaline metals.
One thing that I like to do to really strengthen this connection between the reactions with the
water and the reactions with the acid is to explore in a little bit more detail what's
going on with magnesium. And this is where the reaction of magnesium with steam comes into play.
So if you leave magnesium for a period of time, you can actually collect some
hydrogen gas off of this, but you can see the reaction that I'm showing here, that was
collected over about a 24-hour period, we were able to produce a sensible amount of hydrogen
that we could then burn off. You can see the phenolphthalein also there, changing colour,
indicating that we're producing some hydroxide ions in the solution as well, but, of course,
when it comes to sort of showing a reaction, you may not necessarily have the ability to
immediately cut back the following day for some students. And this is where being able to speed
things up by working at a higher temperature and reacting the magnesium with some steam
can help us out.
You can start by wrapping up a 10 to 15 centimetre coil of magnesium
into a coil about a few centimeters in length and about half a centimeter to a centimetre
in diameter that will neatly fit inside your tube. Do be aware, of course,
that you don't leave sections of long magnesium ribbon around in the lab, There's potential theft
risk associated with that as well. We're going to be using a Pyrex or borosilicate boiling
tube to make sure that it can withstand the high temperatures that we're going to be operating at.
And once you get the experiment ready, make sure that both audience and demonstrator are protected by
safety screens. You should be wearing splash-proof goggles for this experiment.
This experiment, by the way, should never be attempted with more reactive metals like calcium or the alkali metals
and definitely not with magnesium powder either.
Once you've got your kit set up, you'll need to get your Pyrex boiling tube and insert some mineral wool down into the bottom
and you can then soak that with some water. Now I find it kind of handy to actually load this
from an angle and then use the pipettes to load from the top of the mineral wool as I'm doing so.
That gives me an idea of whether or not it's being close to being saturated at that point.
Once the mineral wool is wet, you can then push in your magnesium coil
and add a bung to the ends. Through the end of the bung, there is a small section of glass
tubing that's protruding about two centimetres to make sure that we can safely light the magnesium afterwards.
With the students positioned two metres away wearing eye protection
and with you wearing splash-proof goggles you can now begin to heat directly below the magnesium with a heating flame from a Bunsen.
It'll take about 30 seconds for the magnesium to light,
and once it does, immediately move the flame to the water.
You can now light the end of the glass tubing to show the evolved hydrogen,
linking up the experiment with that of the other metals from earlier.
Sometimes once you finish the experiment, you'll notice the borosilicate tube will crack.
Even if it doesn't, the glass will still be severely weakened and should not be reused.
Rather than reusing it, rinse in at least 500 cm cubed of water. You might get
a few bubbles or even a pop as magnesium silicide reacts to produce pyrophoric silanes and then you
can then dispose of this in your regular glass disposal.
So a classic experiment magnesium with steam. Give it a go. And we'll see you in a couple of months to have a look at some jelly babies.