Bases
What makes a base act like a base?
- Bases are substances which can neutralise an acid, forming a salt and water
- The term base and alkali are not the same
- A base which is water-soluble is referred to as an alkali
- So, all alkalis are bases, but not all bases are alkalis
- Alkalis have pH values of above 7
- In basic (alkaline) conditions red litmus paper turns blue
- Bases are usually oxides, hydroxides or carbonates of metals
- The presence of the OH- ions is what makes the aqueous solution an alkali
- One unusual base is ammonia solution
- When ammonia reacts with water it produces hydroxide ions
Some Common Alkalis and the Ions they Contain
Examiner Tip
Aqueous ammonia and ammonium hydroxide are the same thing. When ammonia gas dissolves in water it forms ammonium hydroxide. Be careful to use the correct terminology: ammonia is the gas, NH3, ammonium is the ion present in ammonium compounds, NH4+
