Reactions of Alkali Metals (WJEC GCSE Chemistry)
Revision Note
Reactions of Alkali Metals
You need to be able to describe the reactions of the first three alkali metals with water, oxygen and the halogens
This includes providing reaction equations to show what is happening
Alkali metals react readily with oxygen and water vapour in air, so they are usually stored in oil to stop them from reacting
Reactions with Water
Alkali metals react with water to form a metal hydroxide and hydrogen gas
The reactions of the alkali metals with water get more vigorous as you descend the group, as with the other reactions
Summary table for the reactions of Group 1 metals and water
Element | Reaction | Observations |
|---|---|---|
Li | lithium + water → lithium hydroxide + hydrogen 2Li (s) + 2H2O (l) → 2LiOH (aq) + H2 (g) |
|
Na | sodium + water → sodium hydroxide + hydrogen 2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) |
|
K | potassium + water → potassium hydroxide + hydrogen 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g) |
|
Rubidium, caesium and francium will react even more vigorously with air and water than the first three alkali metals
Of the alkali metals, lithium is the least reactive (as it is at the top of Group 1) and francium would be the most reactive (as it’s at the bottom of Group 1)
All Group 1 metals produce alkaline solutions (> pH 7) when they react with water, hence the name alkali metals
Lithium will produce a solution of lithium hydroxide; sodium will produce a solution of sodium hydroxide and so on.
If universal indicator is added to the solution, it will turn purple / blue.
Examiner Tips and Tricks
A common mistake students make when they are asked to give observations of these reactions is that 'hydrogen is formed'.
This is not an observation. Observations would include fizzing / hissing etc.
Reactions with Oxygen
The alkali metals react with oxygen in the air forming metal oxides, which is why the alkali metals tarnish when exposed to the air
The metal oxide produced is a dull coating which covers the surface of the metal
When placed in a glass jar of oxygen, the metals react vigorously with the oxide forming as white smoke
Summary table for the reactions of Group 1 metals and oxygen
Element | Reaction |
|---|---|
Li | lithium + oxygen → lithium oxide 4Li (s) + O2 (g) → 2Li2O (s) |
Na | sodium + oxygen → sodium oxide 4Na (s) + O2 (g) → 2Na2O (s) |
K | potassium + oxygen → potassium oxide 4K (s) + O2 (g) → 2K2O (s) |
Reactions with Chlorine
All the Group 1 metals react vigorously when heated with chlorine gas to form salts called metal chlorides
This reaction becomes more vigorous moving down the group, the same as with the reaction between the metals and water
Summary table for the reactions of Group 1 metals and halogens
Element | Reaction | Observations |
|---|---|---|
Li | lithium + halogen → lithium halide 2Li (s) + X2 (g) → 2LiX (s) Where X is Cl or Br or I |
|
Na | sodium + halogen → sodium halide 2Na (s) + X2 (g) → 2NaX (s) Where X is Cl or Br or I |
|
K | potassium + halogen → potassium halide 2K (s) + X2 (g) → 2KX (s) Where X is Cl or Br or I |
|
Examiner Tips and Tricks
For each reaction of Group 1 metals, make sure you can write the word and symbol equations (with state symbols!)
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