SPM Chemistry Form 4 Notes – Electrochemistry (Part 5)

by BerryBerryTeacher

in Berry Reference (Notes)

One important factor governing the process of electrolysis is the types of electrodes used. This Part 5 of Berry Berry Easy notes for SPM Form 4 Chemistry on Electrochemistry is a further add-on to the two previous factors affecting electrolysis. The first two being the positions of ions in the electrochemical series and effects of concentration of ions in the solution. So do read on the previous two posts, Part 3 and 4 in this series of notes on Electrochemistry before proceeding on to this post (if you have not read them yet).

[Tips: Just to give Berry Readers an idea of how important the types of electrodes can influence electrolysis, it is rumoured in 2008 that there is a new electrode which allows the electrolysis of hydrogen to be 1000% faster than the conventional method. Presently, conventional electrolysis of hydrogen uses precious metal catalyst which is still relatively slow and inefficient. The new method uses alkaline electrolysis process in conjunction with nanatechnology, allowing the electrode's catalytic surface area to be larger. While this information might be not exactly useful, unless it is to quote an example in essays, but it is good to know the actual effect of electrodes in the electrolysis process.]

SPM Chemistry Form 4 Notes – Electrochemistry (Part 5)

Voltaic Cell

Voltaic Cell

3. Types of electrodes used in the electrolysis

There are 2 important notes:

  • Inert electrodes: Carbon and platinum (Both of these electrodes do not react with the electrolytes or products of electrolysis)
  • Active electrodes: Silver, copper and nickel (Active anode ionises and concentration of cations in the electrolyte does not change)

Example 1:

Carbon electrode (inert electrode) in the electrolysis of 0.1 mol dm-3 of aqueous 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). A brown deposited on the cathode.
  • Anode (positive electrode): OH- move to the anode (ions are selectively discharge). Gas bubbles are produced. A colourless gas liberates and it ignites the glowing wooden splinter.
  • The intensity of the blue colour solution decreases because the concentration of copper(II) ions decreases.

Example 2:

Copper electrode (active electrode) in the electrolysis of 0.1 mol dm-3 of aqueous 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-)
  • Anode (positive electrode): OH- and SO42- are not discharged. Copper anode dissolves by releasing electrons to form copper(II) ions, Cu2+. Copper anode becomes thinner.
  • Cathode (negative electrode): Cu2+ move to the cathode (ions are selectively discharge) to form copper metal. Copper cathode becomes thicker.
  • The intensity of the blue colour solution remains unchanged because the concentration of copper(II) ions remains the same.

Other examples:

3. Copper electrode (active electrode) in the electrolysis of 0.1 mol dm-3 of aqueous copper(II) nitrate, Cu(NO3)2 solution

4. Silver electrode (active electrode) in the electrolysis of 0.1 mol dm-3 of aqueous silver nitrate, AgNO3 solution

This ends Part 5. The next part, Part 6 of short notes from Berry Berry Easy on SPM Form 4 Chemistry – Electrochemistry will focus on the prediction of electrolysis products of aqueous solutions and industrial applications of electrolysis.

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