CIE AS Chemistry (9701) exams from 2022

Revision Notes

2.2.3 Thermal Decomposition of Nitrates & Carbonates

Group 2: Thermal Decomposition of Nitrates & Carbonates

  • 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:

Group 2 - General Equation Thermal Decomposition Carbonates, downloadable AS & A Level Chemistry revision notes

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

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

 

Group 2 - Thermal Decomposition Carbonates, downloadable AS & A Level Chemistry revision notes

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

 

Group 2 - Thermal Decomposition Nitrates, downloadable AS & A Level Chemistry revision notes

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:

 

Group 2 - General Equation Thermal Decomposition Nitrates, downloadable AS & A Level Chemistry revision notes

 

  • 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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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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