SPM Chemistry Form 4 Notes – Electrochemistry (Part 2)

by BerryBerryTeacher

in Berry Reference (Notes)

Electrolysis is a very important process in chemistry which has not only academic importance but also industrial applications. Without going to far into that, electrolysis is simply a method of utilising electric current (direct current) to force a chemical reaction which would not have happened normally (non-spontaneous). This is one of the most asked question in SPM Chemistry, so Berry Berry Easy would like to provide notes, Part 2 of SPM Chemistry Form 4 short notes on Electrochemistry. In this part, you’ll be exposed to the electrolysis of molten compounds and some relevant examples such as molten magnesium oxide, molten lead(II) bromide and molten naphthalene. So read the following post to understand electrolysis of molten compounds.

[Tips: For those who fail to see the underlying concept of electrolysis, then understanding the origin of the Greek word would give obvious hints about the process. Electrolysis comes from two words, from the Greek words "Elektron" and "Lysis" which mean "amer" and "to separate", respectively. The key point here is 'separation'. So do remember the origin if you forget what electrolysis is all about.]

SPM Chemistry Form 4 Notes – Electrochemistry (Part 2)

Voltaic Cell

Voltaic Cell

Electrolysis of Molten Compounds

  • Electrolysis (with battery / electricity current) is a process of decomposition / breaking down / separation of a compound (electrolyte) into its constituent elements when electric current passes through it.

Important definition

Anode Electrode connected to the positive terminal (+) of a battery
Cathode Electrode connected to the negative terminal (-) of a battery
Anion Negatively-charged ion. Example: Cl-, SO42- and O2-
Cation Positively-charged ion. Example: Na+, Zn2+ and Al3+

Classification of electrodes

Inert electrodes Electrodes that do not take part in chemical reactions during electrolysis Carbon or platinum
Active electrodes Electrodes that take part in chemical reactions during electrolysis Copper or zinc

Example 1:

Molten magnesium oxide, MgO

  • Ions: Magnesium ions (Mg2+) & oxide ions (O2-)
  • Cathode (Negative electrode): Mg2+ move to the cathode
  • Anode (Positive electrode): O2- move to the anode
  • Electrons flow from anode to the cathode through the wire
  • Can conduct electricity

Example 2:

Molten lead(II) bromide, PbBr2

  • Ions: Lead(II) ions (Pb2+) & bromide ions (Br - )
  • Cathode (Negative electrode): Pb2+ move to the cathode
  • Anode (Positive electrode): Br - move to the anode
  • Electrons flow from anode to the cathode through the wire
  • Can conduct electricity

Example 3:

Molten naphthalene

  • Ions: No ions present (naphthalene is covalent compound which consists of molecules = uncharged particles)
  • No electrons flows
  • Cannot conduct electricity

This is end of Part 2, the next part of short notes from Berry Berry Easy on SPM Form 4 Chemistry – Electrochemistry will be on the main title of Electrolysis of Aqueous compounds focusing on the smaller subtopic of positions of ions in the electrochemical series.

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