SPM Chemistry Form 4 Notes – Electrochemistry (Part 3)

by BerryBerryTeacher

in Berry Reference (Notes)

The underlying principle of electrolysis requires ions movement. As such, electrolysis will not work when an object is solid as there will not be any movement of ions, hence electricity cannot flow. In the previous part, the ions are allowed to move by making molten compound of the electrolyte (by melting it). In the next few part, Berry Readers will be looking at dissolving the electrolytes in water in the next few parts. So this post from Berry Berry Easy on SPM Form 4 Chemistry for Electrochemistry – Part 3 is focused on the electrolysis of aqueous solutions with first important factor of positions of ions in the electrochemical series.

[Tips: It's always good to be memorising the electrochemical series for easy retrieval during exams. Try to use mnemonic methods to recall the sequence.]

SPM Chemistry Form 4 Notes – Electrochemistry (Part 3)

Voltaic Cell

Voltaic Cell

Electrolysis of Aqueous Compounds (dissolved in water, H2O)

There are three important factors to determine the types of ions to be discharged at the electrodes.

  1. Positions of ions in the electrochemical series
  2. Concentration of ions in the solution
  3. Types of electrodes used

1. Positions of ions in the electrochemical series

The lower the position of the ion in the electrochemical series, the easier the ion is selectively discharged.

Electrochemical series:

Cation Anion
K+ F-
Na+ SO42-
Ca2+ NO3-
Mg2+ Cl-
Al3+ Br-
Zn2+ I-
Fe2+ OH-
Sn2+
Pb2+
H+
Cu2+
Hg+
Ag+
Au+

Example 1:

0.5 mol dm3 of potassium chloride, KCl solution

  • Positive ions (cations): potassium ions (K+) and hydrogen ions (H+),
  • Negative ions (anions): chloride ions (Cl-) and hydroxide ions (OH-)
  • Cathode (negative electrode): H+ move to the cathode (ions are selectively discharge)
  • Anode (positive electrode): OH- move to the anode (ions are selectively discharge)

Example 2:

0.1 mol dm3 of copper(II) sulphate, CuSO4 solution

  • Positive ions (cations): copper ions (Cu2+) and hydrogen ions (H+),
  • Negative ions (anions): sulphate ions (SO42-) and hydroxide ions (OH-)
  • Cathode (negative electrode): Cu2+ move to the cathode (ions are selectively discharge)
  • Anode (positive electrode): OH- move to the anode (ions are selectively discharge)

The next part, Part 4 of short notes from Berry Berry Easy on SPM Form 4 Chemistry – Electrochemistry will be on the main title of Electrolysis of aqueous compounds while focusing on the subtopic of effects of concentration of ions in the solution.

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