Bases (Edexcel IGCSE Chemistry: Double Science)

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