The ‘Activity’ Series

The activity series lists metals according to ease in which they lose electrons  (in other words, in order of how the get oxidised).

They are ranked in order of those that lose electrons the most easily first, to those that lose electrons most easily last. In other words, those that are most easily oxidised go at the top. Another way of thinking of it is that the reducing agents are at the top.

You don’t have to learn this list as it is given in table 25 of the data book.

Here is a selection of that list:

The list is put together by observing how these metals react with water, acids and salt solutions of each other (displacement reactions).

At first glance, nothing may seem unusual about this list but on closer inspection you may see three anomalies.

Firstly, lithium is at the top, not potassium. Hang on, isn’t potassium more reactive than lithium? I’m sure you have seen your teacher demonstrate the reaction on both of these elements with water – and potassium is the clear winner. Well, like most things in chemistry, what you think you see if not always what is actually happening!

If we measure the energy change for these reactions they are actually nearly the same. Clearly, potassium is more reactive and seemingly more energetic but it is only the rate at which this energy is given off is greater.

The reactions also involve hydration reactions as the metal ion formed will be a hydrated one – and in this case the formation of hydrated lithium ions is more energetic than potassium – so lithium wins and gets to the top of the list!

The other anomalies are hydrogen and carbon.

No, there is not some rule saying that they are now metals …. They clearly are not (although graphite can conduct electricity … but let’s not go there!)

Carbon and hydrogen are in the list to help with metal extraction and reactions with water.

Any metal higher than carbon in the activity series than carbon is unable to be reduced by carbon to form to the metal  – the metal will be the better reducing agent. Any metal higher than carbon will likely be extracted by electrolysis. Those below carbon will be able to  be extracted by some sort of displacement reaction (eg, Iron from Iron (III) oxide in the blast furnace.

Those above hydrogen will react with water (and in doing so will displace hydrogen to form hydrogen gas). Again those underneath will not react.

What about something like magnesium though? This does not react with water – or does it? Well, it will react with steam (which is chemically the same as water) but it will also react with cold water … it just may take a while – so slowly in fact that if not enough water is used  the water may evaporate away before the metal reacts!