Bases (Edexcel IGCSE Chemistry (Modular))

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