EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.6.4 Bases

EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.6.4 Bases

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 oxideshydroxides 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

1.7-Equilibria-Table-1_Common-Alkalis

 

Exam 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, NH3ammonium is the ion present in ammonium compounds, NH4+

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