Reactions of Alkali Metals (WJEC GCSE Chemistry)

• 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)	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. 

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	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