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:

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

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