SPM Chemistry Form 4 Notes – Electrochemistry (Part 4)

by BerryBerryTeacher

in Berry Reference (Notes)

This Part 4 of Berry Berry Easy notes for SPM Form 4 Chemistry on Electrochemistry is a continuation of Part 3 which was on the electrolysis of aqueous solutions. In the previous post, the focus was on the positions of ions in the electrochemical series. This time is is on the effects of concentration of ions in the solution. So if you have not read the previous parts, please read it first before hopping onto this part.

[Tips: The effects of concentration of ions in solutions on affecting electrolysis of aqueous solution is only significant if the two ions are not too far apart in the electrochemical series.]

SPM Chemistry Form 4 Notes – Electrochemistry (Part 4)

Voltaic Cell

Voltaic Cell

2. Effect of concentration of ions in the solution

The concentration of a particular type of ion is high = ion more likely to be discharged in electrolysis.

Example:

2.0 mol dm-3 of lead(II) chloride, PbCl2 solution

  • Positive ions (cations): lead(II) ions (Pb2+) and hydrogen ions (H+),
  • Negative ions (anions): chloride ions (Cl-) and hydroxide ions (OH-)
  • Cathode (negative electrode): Pb2+ move to the cathode (ions are selectively discharge)
  • Anode (positive electrode): Cl- move to the anode (ions are selectively discharge)

Nevertheless, if the two ions are placed very far apart in the electrochemical series, the concentration aspect becomes insignificant.

Example 1:

2.0 mol dm-3 of sodium bromide, NaBr solution

  • Positive ions (cations): sodium ions (Na+) and hydrogen ions (H+),
  • Negative ions (anions): bromide ions (Br-) and hydroxide ions (OH-)
  • Cathode (negative electrode): H+ move to the cathode (ions are selectively discharge)
  • Anode (positive electrode): Br - move to the anode (ions are selectively discharge)

Example 2:

2.0 mol dm-3 of lead(II) nitrate, Pb(NO3)2 solution

  • Positive ions (cations): lead(II) ions (Pb2+) and hydrogen ions (H+),
  • Negative ions (anions): chloride ions (NO3-) and hydroxide ions (OH-)
  • Cathode (negative electrode): Pb2+ move to the cathode (ions are selectively discharge)
  • Anode (positive electrode): OH - move to the anode (ions are selectively discharge)

This ends Part 4. The next part, Part 5 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 dwelling on the subtopic of types of electrodes used in the electrolysis.

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