Redox Reactions

This lesson covers:

  1. The definitions of 'oxidation' and 'reduction'
  2. How redox reactions occur
  3. How to write ionic equations and half equations

Oxidation and reduction - oxygen or electrons?


The terms 'oxidation' and 'reduction' can be a bit confusing, because we can describe them in terms of the gain / loss of oxygen, or the gain / loss of electrons. 

In terms of oxygen: oxidation is the gain of oxygen, and reduction is the loss of oxygen.

Illustration showing oxidation and reduction in terms of oxygen and electrons.

For electrons it's the opposite way around. An easy way to remember it is by remembering the phrase 'OIL RIG'.

Oxidation Is Loss      Reduction Is Gain

Just remember that OIL RIG only works for electrons, not oxygen.

Illustration of the letter E symbolising electron in the context of reduction.

With respect to electrons, reduction is:

The loss of electrons

The gain of electrons

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Which of these reactions is an example of oxidation?

Ca  ➔  Ca2+  +  2e-

Ca2+  +  2e-  ➔  Ca

Ca2+  ➔  Ca  +  2e-

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Illustration of a metal reacting with acid in a beaker, showing a redox reaction with bubbles forming.

When a metal reacts with an acid, a redox reaction takes place.


The metal ions lose electrons, so we say they've been .


The hydrogen ions from the acid gain electrons, so we say they've been .

oxidised
reduced

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Sodium reacts with iron sulphate. 


Select the two half equations involved in this process.

Fe2+ + 2e-  ➔ Fe

Na+ + e- ➔ Na  

Na  ➔  Na+  +  e-

Fe  ➔ Fe2+ + 2e-

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Select the ion being oxidised in the following ionic equation:


2Li  +  Zn2+  ➔  2Li+  +  Zn

Lithium

Zinc

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Diagram showing a species being oxidised and another species being reduced.

Reduction and oxidation rarely happen on their own.

Usually a reaction involves one species being reduced, and another being oxidised.

(a 'species' just means atom / ion / molecule)


What do we call these reactions? 

Addition reaction

Oxiduction

Thermal decomposition

Redox

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Select the spectator ion present in the following equation:


2K  +  CuCl2  ➔  2KCl  +  Cu

Carbon

Potassium

Copper

Chloride

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CuSO4 + Mg ➔ MgSO4 + Cu


Which of the following statements is true about the reaction of copper(II) sulfate with magnesium?


Magnesium atoms are oxidised

Magnesium atoms are reduced

Copper ions are oxidised

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