(a)(i) Define oxidation in terms of electron transfer. (ii) Write balanced equations for the half reactions for the following changes in acidic solution: Mn...
Question 1 Report
(a)(i) Define oxidation in terms of electron transfer.
(ii) Write balanced equations for the half reactions for the following changes in acidic solution: Mn0\(^-_4\) + Fe\(^{2+}\) —> Mn\(^{2+}\) + Fe\(^{3+}\)
(b)(i) Distinguish between an electrolytic celI and an electrochemical cell.
(ii) Sketch a cell for the electrolysis of molten magnesium chloride. Lable the anode and the cathode and indicate the direction of electron flow. Give the electrode reactions.
(iii) Give one reason why a platinum anode is not suitable for the eloctrolysis in (b)(i) above.
(c) Calculate the mass of lead that would be deposited from a solution of lead (II) trioxonitrate by the same quantity of electrically depositing 1.35g of copper. (Cu = 63.5, Pb = 207)
Answer Details
(a)(i) Oxidation in terms of electron transfer
Oxidation is the process in which an atom, ion or molecule loses electron(s).
Example:
\[Fe^{2+} \rightarrow Fe^{3+} + e^-\]
(a)(ii) Balanced half-reactions in acidic solution
Oxidation half-reaction:
\[Fe^{2+} \rightarrow Fe^{3+} + e^-\]
Reduction half-reaction:
\[MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O\]
(b)(i) Difference between an electrolytic cell and an electrochemical cell
| Electrolytic cell | Electrochemical cell (voltaic/galvanic cell) |
|---|---|
| Uses electrical energy from an external source to cause a non-spontaneous chemical reaction. | Uses a spontaneous chemical reaction to produce electrical energy. |
| Converts electrical energy to chemical energy. | Converts chemical energy to electrical energy. |
| The cathode is negative and the anode is positive. | The anode is negative and the cathode is positive. |
(b)(ii) Electrolysis of molten magnesium chloride
Two inert electrodes, such as graphite electrodes, are dipped into molten magnesium chloride and connected to a direct-current source.
DC source (battery)
(+) (−)
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