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

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

Element	Reaction	Observations
Li	lithium + water → lithium hydroxide + hydrogen 2Li (s) + 2H₂O (l) → 2LiOH (aq) + H₂ (g)	Relatively slow reaction Fizzing Lithium moves on the surface of the water
Na	sodium + water → sodium hydroxide + hydrogen 2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)	More vigorous fizzing Moves rapidly on the surface of the water Dissolves quickly
K	potassium + water → potassium hydroxide + hydrogen 2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)	Reacts more vigorously than sodium Burns with a lilac flame Moves very rapidly on the surface Dissolves very quickly

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.

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.

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

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)

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

Element	Reaction	Observations
Li	lithium + halogen → lithium halide 2Li (s) + X₂(g) → 2LiX (s) Where X is Cl or Br or I	A red flame A white solid is formed
Na	sodium + halogen → sodium halide 2Na (s) + X₂ (g) → 2NaX (s) Where X is Cl or Br or I	A yellow flame A white solid is formed
K	potassium + halogen → potassium halide 2K (s) + X₂ (g) → 2KX (s) Where X is Cl or Br or I	A lilac flame A white solid is formed

For each reaction of Group 1 metals, make sure you can write the word and symbol equations (with state symbols!)

Reactions of Alkali Metals (WJEC GCSE Chemistry: Combined Science)