Edexcel A Level Chemistry:复习笔记2.1.3 Redox & Disproportionation

Disproportionation

 

Disproportionation reactions

  • A disproportionation reaction is a reaction in which the same species is simultaneously oxidised and reduced

1.6-Electrochemistry-Disproportion-Reaction

Example of a disproportion reaction in which the same species (chlorine in this case) has been both oxidised and reduced

Using Oxidation Numbers

Worked Example

Balancing disproportionation reactions

Balance the disproportionation reaction which takes place when chlorine is added to hot concentrated aqueous sodium hydroxide. The products are Cl- and ClO3- ions and water

Answer

Step 1: Write the unbalanced equation and identify the atoms that change in oxidation number:

 

1.6-Electrochemistry-Step-1-Balancing-disproportionation-reactions

Step 2: Deduce the oxidation number changes:

1.6-Electrochemistry-Step-2-Balancing-disproportionation-reactions

Step 3: Balance the oxidation number changes:

1.6-Electrochemistry-Step-3-Balancing-disproportionation-reactions

 

Step 4: Balance the charges

 

1.6-Electrochemistry-Step-4-Balancing-disproportionation-reactions

Step 5: Balance the atoms

1.6-Electrochemistry-Step-5-Balancing-disproportionation-reactions

Worked Example

Oxidation and reduction

In each of the following equations, state which reactant has been oxidised and which has been reduced.

  1. Na++ Cl- →  NaCl
  2. Mg + Fe2+  →  Mg2+ + Fe
  3. CO + Ag2O  →  2Ag + CO2

Answer 1:

    • Oxidised: Cl- as the oxidation state has increased by 1
    • Reduced: Na+ as the oxidation state has decreased by 1

Answer 2:

    • Oxidised: Mg as the oxidation state has increased by 2
    • Reduced: Fe2+ as the oxidation state has decreased by 2

Answer 3:

    • Oxidised: C as it has gained oxygen
    • Reduced: Ag as it has lost oxygen

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