SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 5)

by BerryBerryTeacher

in Berry Reference (Notes)

Reactivity Electrochemical series!!! It is one of the most memorable thing to memorise in the whole of secondary school chemistry. (The Berry Berry Teacher will bet that 10-20 years down the road when you are working, you’ll still ask your former classmates if they can still recite the reactivity electrochemical series. So, today’s notes is focused on the reactivity electrochemical series under Part 5 of the SPM Form 5 Chemistry notes on “Oxidation and Reduction”. In addition to memorising the table below, try also to understand the trend when you move upwards and downwards the series. (Do check out the mnemonic method to memorise reactivity electrochemical series at the end of the post)

(Legend: “Dark blue fonts” represent addition to the notes, “cross-out words” represent those that were wrong in the original edition – Do check out the correction post)

SPM Chemistry Form 5 – Terminology and Concepts: Oxidation and Reduction (Part 5)

Rusting of Iron Nails

Rusting of Iron Nails

Displacement of Metals from Their Salt Solution

More electropositive metal is more reactive metal and it will displace a less reactive metal from the solution.

Reactivity Electrochemical Series

Metal Equation
Potassium K (s) –> K+ (aq) + e
Sodium Na (s) –> Na+ (aq) + e
Calcium Ca (s) –> Ca2+ (aq) + 2e
Magnesium Mg (s) –> Mg2+ (aq) + 2e
Aluminium Al (s) –> Al3+ (aq) + 3e
Zinc Zn (s) –> Zn2+ (aq) + 2e
Iron Fe (s) –> Fe2+ (aq) + 2e
Tin Sn (s) –> Sn2+ (aq) + 2e
Lead Pb (s) –> Pb2+ (aq) + 2e
Hydrogen H (s) –> H+ (aq) + e
Copper Cu (s) –> Cu2+ (aq) + 2e
Silver Ag (s) –> Ag+ (aq) + e

Going up the table:

  1. Tendency of metals to form positive ions increases.
  2. Electropositivity increases.
  3. Strength as reducing agent increases.

(The focus should be on the strength of the reducing agent)

Going down the table:

  1. Tendency of metals to receive electrons increases.
  2. Electropositivity decreases.
  3. Strength as oxidising agent increases.

(The focus should be on the strength of the oxidising agent)

a) Magnesium ribbon + Lead(II) nitrate solution

  • Mg (s) –> Mg2+ (aq) + 2e
    Oxidation
    : Magnesium ribbon, Mg is a reducing agent because it is more electropositive than lead.
  • Pb2+ (aq) + 2e –> Pb (s)
    Reduction
    : Lead(II) ion, Pb2+ is an oxidising agent because it receives/accepts two electrons to become lead.
  • Observation:
    i) Deposition of dark brown solid (lead) on the magnesium ribbon.
    ii) The magnesium ribbon dissolves.
  • Overall reaction: Pb2+ (aq) + Mg (s) –> Pb (s) + Mg2+ (aq)

b) Zinc strip + Copper(II) sulphate solution

  • Zn (s) –> Zn2+ (aq) + 2e
    Oxidation
    : Zinc strip, Zn is a reducing agent because it is more electropositive than copper.
  • Cu2+ (aq) + 2e –> Cu (s)
    Reduction
    : Copper(II) ion, Cu2+ is an oxidising agent because it receives/accepts two electrons to become copper.
  • Observation:
    i) Deposition of brown solid (copper) on the zinc strip.
    ii) The blue colour of CuSO4 becomes paler / The blue solution turns to colourless.
    iii) The zinc strip dissolves.
  • Overall reaction: Cu2+ (aq) + Zn (s) –> Cu (s) + Zn2+ (aq)

c) Copper strip + Magnesium sulphate solution

  • No changes.
    Magnesium is more electropositive than copper.
  • Observation:No changes.
    There is no redox reaction occurs.

Mnemonic method for memorising the reactivity electrochemical series

Students typically will form sentences (sometimes naughty ones) to memorise the series in a mnemonic way. Berry Berry Easy would like to share with you some famous ones such as:

  • Paddy Still Could Marry A Zulu In The Lovely Honolulu Causing Many Strange Gazes.
    P
    otassium Sodium Calcium Magnesium Aluminium Zinc Iron Tin Lead Hydrogen Copper Mercury Silver Gold
    (In the above statement, there is addition of Mercury and Gold. No harm memorising those too)

{ 2 comments… read them below or add one }

July 8, 2012
July 9, 2012

Previous post:

Next post: