Thursday 26 February 2015

3.4.1 - Laboratory Activity: Redox reactions in electrolytic and chemical cells


Laboratory Activity 3.4.1:
Redox reactions in electrolytic and chemical cells
Aim: To study the redox reaction occurs in electrolytic and chemical cells
Material:
» Carbon electrode
» Copper(II) sulphate
» Zinc strip
» Copper strip
» Zinc sulphate

Apparatus:
» Carbon electrode
» Ammeter
» Battery
» Connecting wire
» Crocodile clips
» Beaker
» Porous pot
Procedure:

(A) Electrolytic cell
1.
2. Electricity is passed through the copper(II) sulphate solution for 15 minutes.
3. The changes and observations in the experiment are recorded.

(B) Chemical cell
1.
2. About 50cm3, 1mol dm-3 of zinc (II) sulphate, ZnSO4, is filled into a beaker.
3. A porous pot is ¾ filled with 1mol dm-3 of copper sulphate solution.
4. The porous pot is then place into the beaker of copper (II) sulphate solution.
5. The copper strip is place inside the copper (II) solution and the zinc strip into zinc sulphate solution.
6. Both metal plates are connected with connecting wire to a voltmeter.
7. Changes to the voltmeter, metal electrode and electrolyte solution are observed and recorded.
Observation:

(A) Electrolytic cell
Electrode Observation
Anode Colourless gas released. Light up glowing splinter.
Cathode Shinning brown substance is formed
Colour of electrolyte Blue colour solution fades

(B) Chemical cell
Electrode Observation
Voltmeter's pointer Deflects
Anode The zinc plate dissolves
Cathode Shinning brown substance is formed
Colour of electrolyte Blue colour solution fades
Analysis:

(A) Electrolytic cell
At anode (+) At cathode (-)
Half ionic equation:
4OH(aq) → 2H2O(l) + O2(g) + 4e
Half ionic equation:
Cu2+(aq) + 2e → Cu(s)
Oxidation → hydroxides ion release electron Reduction → copper(II) ion receive electron
Hydroxides ion acts as reducing agent. Copper(II) ion acts as oxidising agent.
Oxygen gas is collected Copper metal is deposited

(B) Chemical cell
At anode (+) At cathode (-)
Half ionic equation:
Zn(s) → Zn2+(aq) + 2e
Half ionic equation:
Cu2+(aq) + 2e → Cu(s)
Oxidation → zinc release electron Reduction → copper(II) ion receive electron
Zinc acts as reducing agent. Copper(II) ion acts as oxidising agent.
Zinc gas is collected Copper metal is deposited
Electron flow from the zinc plate to the copper plate through the outer circuit.
An electric current is produced as shown in the deflection of voltmeter.
Conclusion:

Oxidation process and reduction process occur in both electrolytic and chemical cells.


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