This demonstration shows the reactions of lithium, sodium and potassium
on heating in air, in chlorine and with water
and also shows some of their physical properties. We hope to show the similarities
between the metals and also their trend in reactivity.
Visibility can be a problem when doing these sets of
experiments due to the very small amounts of metal that you'll be using.
If you have access to a video camera and projector
this could work very well for your students to be able to see the small detail.
There are a lot of observations to be made by the audience
and it is probably worthwhile getting them to draw up a table
like this one to fill in while they watch. This could be extended to include room for
predictions about rubidium and caesium.
For greatest impact do the reactions of potassium last as they are the most spectacular.
Periodic table order seems logical
and builds to the most spectacular at the end.
The first experiment is going to be heating in air.
In preparation we need to cut some of the metal and this is an ideal opportunity
to show some of the physical properties. First of all
we should point out that all the alkaline metals that we are using are stored in oil.
Take some of the metal out of the container using some tweezers and place on a tile.
We're going to cut a small amount of the metal off this large chunk.
As you can see with the lithium, it's quite difficult to cut.
There we go. And you can see clearly the shiny silver surface. Over time this this does tarnish.
I'm going to put this big chunk of lithium back in the container.
A second physical property that can be demonstrated
is the ability of the metal, in this case lithium, to conduct electricity.
I'm going to cut a small piece of lithium. There you go.
Pick up the piece of lithium and drop it on to petri dish.
Pass it around the class so that the audience can get an impression of how light in weight it is.
Warn students not to touch the metal,
taping the lid on to the petri dish if necessary. Next, you will need to cut
a 3 mm cube piece of metal in order to heat in air.
Before we heat in air, you need to dry off the oil from the metal using some paper tissue.
We no longer recommend using hexane to dissolve the oil
because there have been fires when washing up due to some residues.
Place the little bit of metal on a flat brick.
When heating the metal, you need to use a roaring bunsen flame
and position the metal at the top of the blue cone which is the hottest part.
You can test the white residue with moist indicator paper.
Next we're going to look at reaction with sodium metal.
Again, indicate to your class that sodium is stored in oil
to protect it from reacting with moist air.
We need to cut a piece of sodium off this large piece.
You can see the lovely shiny silver surface
that tarnishes much quicker than the lithium in air.
I'll just put this back in here.
We can use a circuit tester to show that it conducts electricity.
Cut off a small piece ready to heat in air.
Dry off the piece of sodium
and place it on a brick ready to heat.
Again, with a roaring bunsen flame, you can see it melting
and reacting with the air.
We can again test the residue of sodium oxide with some moist indicator paper.
This is the reaction of potassium in air.
Again, the potassium is stored under oil and we need to cut a piece off.
You can see it is much easier to cut. This is much softer.
There's the shiny silver surface which tarnishes
quickly in air, much quicker than with the lithium and sodium.
Again, we can use the circuit tester to show clearly that it conducts electricity.
And then we need to cut off a small piece to heat it in air.
It very quickly melts.
You can just see a purple flame.
For this you will need some previously prepared chlorine stored in a gas jar
sealed with Vaseline. You should make sure that
there is a green colour of the gas in the gas jar.
You should also make sure
that the opening of the gas jar is smaller
than the brick so you don't lose the chlorine out
when you put it over the burning piece of metal.
Heat the metal up until it's burning
You can see that one goes much quicker.
Lithium, dry it off with a paper towel.
Put it in the water
When the reaction's finished you can add some indicator.
Add some indicator
To confirm the gas is indeed hydrogen
add a very small piece of clean lithium to a little tap water
in a boiling tube. Wait for a few seconds
and pop the gas with a lighted taper. A squeaky pop.