Edexcel A Level Chemistry:复习笔记2.2.4 Group 2 Carbonates & Nitrates

Group 2 Carbonates & Nitrates

 

  • Thermal decomposition is the breakdown of a compound into two or more different substances using heat

Thermal decomposition of carbonates

  • The Group 2 carbonates break down (decompose) when they are heated to form the metal oxide and give off carbon dioxide gas
  • The general equation for the decomposition of Group 2 carbonates is:

2.2-Group-2-General-Equation-Thermal-Decomposition-Carbonates

The thermal decomposition of Group 2 carbonates to form metal oxides and carbon dioxide gas

 

  • Going down the group, more heat is needed to break down the carbonates

2.2-Group-2-Thermal-Decomposition-Carbonates

The diagram shows the thermal decomposition of magnesium carbonate to form magnesium oxide and carbon dioxide gas

Thermal decomposition of nitrates

  • The Group 2 nitrates break decomposed when they are heated to form the metal oxide, oxygen gas and nitrogen dioxide gas (which is a brown toxic gas)
  • Since the formed nitrogen dioxide gas is toxic, the decomposition of nitrates is often carried out in a fume cupboard

2.2-Group-2-Thermal-Decomposition-Nitrates

The diagram shows the thermal decomposition of magnesium nitrate to form magnesium oxide, oxygen gas and nitrogen dioxide gas

 

  • The general equation for the decomposition of Group 2 nitrates is:

2.2-Group-2-General-Equation-Thermal-Decomposition-Nitrates

  • Going down the group, more heat is needed to break down the nitrates
    • The smaller positive ions at the top of Group II will polarise the nitrate ions more than the larger ions at the bottom of the group
    • The more polarised they are, the more likely they are to thermally decompose

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