Understanding how the reactivity of different metals compare to each other
is important when deciding which metals should be used for a certain job. For example,
it's important to choose the correct metal when making a hot water pipe so it doesn't rust.
You would also need to choose an appropriate metal to make a food can
so that the food stays fresh and the metal does not react with the food to
spoil it. I'm going to be demonstrating three different types of reactions with metals.
The first experiment is an investigation of the alkali metals with water.
This is the exciting one! As it's hazardous, it's only a teacher demonstration but you do need to
know and understand these reactions as part of your chemistry course. I'm going to start with
the reactivity of metals with water. We have three metals to investigate today. They are all in group
one and are known as the alkali metals. Each metal will react more or less vigorously with the water
and you can use your observations to put them into an order of reactivity.
This will allow you to investigate the order of reactivity as you go down group one.
For health and safety reasons today we have put up safety screens and I need to wear eye protection.
I'm going to start with lithium. You'll notice that it's stored in
oil, this is so it doesn't react with the oxygen or any moisture in the air.
I'm now going to cut the lithium so I get a smaller piece.
You'll notice that I can just about cut the lithium with a knife.
The rest of the lithium will go back in the oil.
Look at the surface of the lithium where I have just cut it. It's quite shiny but it
won't stay like this for long because it will rapidly react with the air to become dull.
I'm now going to gently drop this lithium into the trough. Let's observe...
The lithium is slowly moving around and it's floating on top of the water. There's fizzing.
This is also known as effervescence. The lithium is also getting smaller.
We can summarise the observations as follows:
Another substance is being made. To give us a clue about what this is
I can add a few drops of universal indicator to the water.
The universal indicator is turning purple. This is because the reaction makes soluble
lithium hydroxide which is an alkali and contains hydroxide (OH-) ions.
As well as making observations for the reaction of lithium and water, you need to be able to
write word and symbol equations: lithium plus water makes lithium hydroxide plus hydrogen
Now, I'm going to react sodium with water. Again, the sodium is stored in oil
to protect it from reacting with any of the oxygen or moisture in the air.
I'm going to cut the sodium into a smaller piece. The sodium is much softer than the lithium as I'm
able to cut through it easier with the knife. The spare piece of sodium is now going back in the oil.
Notice how the surface where I just cut the sodium is shiny again.
This time, it will react more rapidly with the oxygen in the air to become dull. Again I need
to remove the oil. Now I'm going to gently drop the piece of sodium into a fresh trough of water.
Observe carefully and see if you can see any differences between the sodium and the lithium.
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The sodium is fizzing and it's moving quickly across the water.
It has melted into a ball. I can summarise these observations as follows:
Did you identify what was similar between the reactions of sodium and lithium?
Sodium moved more quickly across the surface and also melted into a ball. However, it's
also important to identify the similarities. Both reactions fizzed and in both reactions the metal
moved across the surface of the water. Let's check to see if we've made an alkali hydroxide again.
I'm going to add a few drops of universal indicator into the water.
Yes, it has turned purple again!
This time we have sodium hydroxide which is also an alkaline solution.
You need to be able to write a word and symbol equation.
sodium plus water makes sodium hydroxide plus hydrogen
Okay, it's time for the final alkali metal. I've left the best till last. Again, potassium is stored in oil.
I'm now going to cut the potassium to get a smaller piece. Notice that that was very soft, much
softer than the other two alkali metals. Again, the spare piece of potassium will go back in the oil.
Notice that again the surface of the potassium is shiny and this time it will react much more
rapidly with the air than both of the metals before it. Again, I'm just going to dab off the oil
and now I'm going to gently put this piece of potassium into the fresh water trough.
Observe carefully...
Out of all three alkali metals, potassium reacts the quickest.
We have therefore slowed down the footage by four times so we can see what happens in more detail.
The potassium is moving very quickly and floating on top of the water.
Fizzing is occurring. Look, the metal has caught fire with a lilac flame and nearly disappeared.
It has self-ignited, producing its own squeaky pop, which tells us that the fizzing is hydrogen gas.
This reaction gives out so much heat the potassium will self-ignite the hydrogen gas
to give this lilac flame. Now, let's check to see if we have made the alkaline solution potassium hydroxide?
Yes, it's turned purple again. That means that we have potassium hydroxide solution.
Now let's have a look at the word and symbol equation with potassium hydroxide. You should be seeing a
pattern with these word and symbol equations now.
potassium plus water makes potassium hydroxide plus hydrogen
The reactivity of the group 1 alkali metals increases as you go down the periodic table.
Link to the additional resources in this video to explore the group 1 metals further.
Now we're going to investigate the reactivity of metals with acid. The acid that I'm using today
is hydrochloric acid and when it reacts with the metals that I have chosen, heat will be given out,
as it's an exothermic reaction. Remember you will need to wear eye protection for this experiment.
I'm going to do the reaction in an insulated cup to try and reduce heat loss. The insulated
cup is not very stable on its own so I'm going to place it inside a beaker to reduce any spillages.
During the reaction, the temperature will rise and I will record this
on a thermometer. The first metal I'm going to use is zinc powder. I'm going
to start by measuring out 20 centimetres-cubed of hydrochloric acid into the measuring cylinder...
...which I'll now pour into the insulated cup.
As I'm measuring temperature change, I must record the temperature at the start of the reaction.
19.5 degrees Celsius.
Here I have a lid with a hole in it so the thermometer will go through the lid.
I'm now going to add two spatulas of zinc powder to the acid in the cup.
It will take a few minutes for the maximum temperature to be reached so now, I will wait.
I'm now ready to do the next metal. The chemicals that we're using today are harmful
so please don't pour them down the sink. Your teacher will provide you
with a container where you can dispose the residues for safe disposal later on.
I can reuse this cup for the next metal by rinsing out the previous metal with water.
What do I need to do to keep this a fair test so I can compare all the metal reactions?
I'm going to use the same apparatus and the same quantities of metal and acid in each of
the reactions. Don't forget to take the starting temperature at the beginning of each reaction.
You can put the metals into an order of reactivity
based on the temperature rise, with the most reactive metal having the highest
temperature rise and the least reactive metal having the lowest temperature rise.
You need to know word and chemical symbol equations for these reactions. Now let's take
a look at the products formed from these reactions. As all of the metals react with hydrochloric acid,
one of the products formed is a chloride salt. The other is a gas. Let's test to see what that gas is.
If I insert a lit splint into this test tube full of the gas, let's see what happens.
There was a squeaky pop, so the gas must be hydrogen. Now let's look at the word and balanced
symbol equations for these reactions. Can you write the balanced symbol equations for magnesium,
iron and zinc with hydrochloric acid to make the chloride salt and hydrogen?
We didn't write an equation for the reaction of copper with hydrochloric acid
because there was no reaction. Check out the additional resources in this video
to explore the reactions of metals and acids further.
So, we have now looked at the reaction of metals with water and acid. As long as the metal reacts,
we can use observations about how quick, vigorous or hot the reaction is to compare the reactivity
of different metals. However, if the metal does not react with water or acid it can be very difficult
to compare the reactivity. In this experiment, I'm going to add a strip of metal to a solution
of a compound of another metal. The more reactive metal will displace the less reactive metal from
its compound, so you will always have a reaction to compare the reactivity of the two metals. I'm going
to do these reactions on a microscale level as these chemicals are harmful to the environment and
need to be disposed of correctly. In this reaction I'm going to use this spotting tile. I've added
labels to this piece of paper, so it is easier to know where I am putting each solution and each
metal. Using a dropping pipette I will add a small amount of each solution to two of the depressions.
Before I start, I must put eye protection on. I'm going to add magnesium sulfate to the first row.
Now I'm going to add zinc sulfate to the second row.
Finally, I will add copper sulfate solution to the third row.
Now I'm going to add small pieces of the metal to each of the rows, starting with magnesium.
Next, I'll add zinc...
...and finally copper.
I did not need to add magnesium to magnesium sulfate, zinc to zinc sulfate
or copper to copper sulfate. Why?
A metal does not displace itself.
Over the next few minutes we need to observe which
reaction mixtures have reacted and which have not. Write down your observations in a results table.
These are the results after leaving it for five minutes. You could take a picture of this with your
phone so you have a record of the results to fill in your results chart. You can see that we have
only had a reaction in three of the experiments. You can see bubbles forming and a darker metal.
Magnesium has reacted with zinc sulfate and copper sulfate and zinc has reacted with copper sulfate.
We can fill in our results chart with a tick or a cross to indicate if there has been a reaction.
Where a reaction has occurred, the metal is more reactive than the metal in the compound. The more
reactive metal has pushed or displaced the less reactive metal from its metal compound. Therefore,
we can put magnesium, zinc and copper into an order of reactivity. Magnesium has reacted with
zinc and copper, therefore it's more reactive than both metals. Zinc does not react with magnesium
sulfate so it does not displace the metal. This means that zinc is less reactive than magnesium.
Zinc does, however, react with copper sulfate and does displace the copper from the metal compound.
Zinc is, therefore, much more reactive than copper. Copper does not react or displace either of the
other metals. Copper is, therefore, the least reactive and goes at the bottom of our list.
We can write word and symbol equations for all of these reactions.
These displacement reactions are also redox reactions.
The more reactive metal is always oxidised and the less reactive metal is reduced. We can now
summarise all the reactions we have completed in this video, and use our observations to produce a
list of the metals in order of reactivity. This is called the reactivity series of metals.
In the first experiment we deduced that potassium was more reactive than sodium and lithium. In the
second experiment we reacted metals with acid and deduced that magnesium was more reactive than zinc,
and zinc was more reactive than iron. In the final experiment we used the displacement reaction of
metals to find out that magnesium was more reactive than zinc, and that copper was the
least reactive metal. As an extension activity, you could design an experiment using a combination of
the reactions we described here to put an unknown metal, for example nickel, into the
order of reactivity that we deduced today. The additional resources can be found in the link.
Thank you for watching, have fun with your experiments.
Inspiring your teaching and learning.