10.08.1 Reactivity of Metals.
Syllabus
Most metals react with Oxygen producing Metal Oxides. These are Oxidation reactions because the metals gain Oxygen.
The least reactive metals, Gold and Platinum do not react with Oxygen
When metals react their atoms form positive ions.
The reactivity of a metal is related to its tendency to form positive ions.
Metals can be arranged in order of their reactivity in a Reactivity Series.
The metals Potassium, Sodium, Lithium, Calcium, Magnesium, Zinc, Iron & Copper can be put in order of their reactivity from their reactions with water and dilute acids.
The non-metals Hydrogen and Carbon are often included in the Reactivity Series.
Students should be able to:
explain reduction and oxidation in terms of loss or gain of Oxygen.
recall and describe the reactions of Potassium , Sodium, Lithium, Calcium, Magnesium, Zinc, Iron & Copper with water or dilute acids and where appropriate, to place these metals in order of reactivity
explain how the reactivity of metals with water or dilute acids is related to the tendency of the metal to form its positive ion
deduce an order of reactivity of metals based on experimental results.
The reactions of metals with water and acids are limited to room temperature and do not include reactions with steam.
What does this mean?
What is reactivity?
Some metals react faster and more violently than others.
We can place metals in order of reactivity (speed of reactions) in a Reactivity Series with the most reactive at the top and least reactive at the bottom.
To find out how reactive metals are we look at what they will react with and compare the speeds at which they react.
Reaction with water
The simplest reaction to study is with water.
In general, Metal + Water --> Metal Hydroxide + Hydrogen.
Caesium and Rubidium explode in water. This makes them very reactive.
Potassium burns, making it a little less reactive.
Sodium, Lithium and Calcium fizz and we could compare the speed of fizzing to see which is most reactive.
Other common metals don't react with water.
So our Reactivity Series at this point would be:
Caesium
Rubidium
Potassium
Sodium
Lithium
Calcium
Most other metals react so slowly with water that we can barely notice
To find the order of reactivity of the other metals we need to look at other reactions.
Reaction with dilute acids.
Magnesium fizzes quickly in dilute acid.
Zinc is a little slower, Iron a little slower still.
Copper, Silver and Gold don't react at all.
So our Reactivity Series would now be:
Caesium
Rubidium
Potassium
Sodium
Lithium
Calcium
Magnesium
Zinc
Iron
Copper, Silver, Gold
But we still wouldn't be able to be sure what order to place the last three metals.
Reaction with Oxygen
Copper, Silver and Gold are not reactive metals, so none of them will react with Oxygen in the air quickly.
But if we were to leave them alone long enough, or speed things up by heating with a Bunsen.
Copper turns black very quickly. Copper Oxide is formed as Oxygen is added - this is Oxidation.
Silver and Gold don't react.
But Silver requires polishing every now and again because it tarnishes (goes dull)
Whereas, Gold never loses its shine (lustre) - so it must be less reactive.
Our Reactivity Series is now:
Caesium
Rubidium
Potassium
Sodium
Lithium
Calcium
Magnesium
Zinc
Iron
Copper
Silver
Gold
This penny is over 120 years old and covered with black Copper Oxide.
The Halfpenny is forty years old and still recognizably Copper
Aluminium - the problem metal!
You'll notice that most Reactivity Series contain Aluminium...
Caesium
Rubidium
Potassium
Sodium
Lithium
Calcium
Magnesium
ALUMINIUM
Zinc
Iron
Copper
Silver
Gold
...even though Aluminium stays shiny in air almost indefinitely and doesn't corrode in water or dilute acid.
The Reactivity Series really measures the relative ease with which metals lose their outer shell electrons to form positive ions - and we can show that Aluminium does this more easily than Zinc or Iron.
The reason it seems unreactive is often because it coats itself with Aluminium Oxide which stops other substances getting at the Aluminium underneath in order to react.
So how can we know exactly where to place it?
Displacement! (See next section)
Additional Notes
Videos
Past Paper Questions
Answer
the (grey) crystals are silver
the copper ions (produced) are blue allow the copper nitrate / compound (produced) is blue
(because) copper displaces silver
Self-test
When you have finished each sub-topic, why not test yourself
