OxidatIon & Reduction in Terms of Electrons (OCR GCSE Chemistry A (Gateway)) : Revision Note
Oxidation & Reduction in Terms of Electrons
Higher Tier Only
For reactions not involving oxygen, we can look at oxidation and reduction in terms of losing and gaining electrons
Oxidation is the loss of electrons
Reduction is the gain of electrons
We can use half and ionic equations to determine which species has been oxidised and reduced in terms of electrons
A displacement reaction occurs between magnesium and copper sulfate:
Mg (s) + CuSO4 (aq) → MgSO4 (aq) + Cu (s)
The ionic equation for this reactions is:
Mg (s) + Cu2+ (aq) → Mg2+ (aq) + Cu (s)
This can be split into two half equations which demonstrate oxidation and reduction individually:
Mg → Mg2+ + 2e–
Cu2+ + 2e–→ Cu
The magnesium atoms are oxidised as they lose electrons
The copper ions are reduced as they gain electrons
Worked Example
Zinc displaces copper from a solution of copper(II)sulfate.
Using ionic equations, determine which species undergoes oxidation and which species undergoes reduction
Answer:
Write the overall balanced symbol equation:
Zn (s) + CuSO4 (aq)→ ZnSO4 (aq) + Cu (s)
Write out the ions separately:
Zn (s) + Cu2+(aq) + SO42- (aq) →Zn2+(aq) + SO42-(aq) + Cu (s)
Eliminate ions that occur on both sides (spectator ions):
Zn (s) + Cu2+(aq) → Zn2+(aq) + Cu (s)
Identify which species has lost or gained electrons
Zinc has lost electrons and been oxidised:
Zn → Zn2+ + 2e-
Copper ions have gained electrons and been reduced:
Cu2+ + 2e- → Cu
Examiner Tips and Tricks
A handy way of remembering definitions for oxidation and reduction for electrons is:
OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain
You've read 0 of your 5 free revision notes this week
Sign up now. It’s free!
Did this page help you?