6.3.3 - Laboratory Activity : Types of electrodes

Laboratory Activity 6.3.3: Types of electrodes

Aim: To study the effect of different electrodes on the type of ions discharged during electrolysis
Problem statement: How does the types of electrodes influence the choice of ion for discharge?
Hypothesis: Type of electrode will influence the choice of ion to be discharged.
Variable:

	»	Fixed variable : Types and concentration of electrolytes
	»	Manipulated variable : Type of electrode
	»	Responding variable : Types of ions discharged at the anode and the cathode

Material: » Distilled water » Copper(II) sulphate solution

Apparatus: » Electrolytic cell » Test tube » Carbon and copper electrodes » Switch » Connecting wires » Crocodile clip » Wooden splinter » Batteries

Procedure:

	►	The animation below shows the arrangement and results of the experiment.
	►	1. Electricity is passed through the copper(II) sulphate solution by using carbon electrodes for 15 minutes. 2. The gases collected at the electrodes are tested and observation are recorded. 3. The experiment is repeated by using copper electrodes . 4. 2 copper plates are cleaned with sandpaper and weighted separately. 5. Electricity is passed through the copper(II) sulphate solution by using copper electrodes for 15 minutes. 6. The cell is disconnected. The copper plates are rinsed with distilled water and weighed separately. The reading are recorded.

Results:

	►	Electrolysis of copper(II) sulphate solution by using carbon electrodes Electrode Observation Inference Anode Colourless gas released. Light up glowing splinter. Oxygen gas is released. Cathode Shinning brown substance deposit Copper is formed Colour of electrolyte Becomes lighter blue in colour Concentration of Cu2+ decreases
	►	Electrolysis of copper(II) sulphate solution by using copper electrodes Electrode Observation Inference Anode Electrode becomes thinner as the weight of the electrode decrease. Electrode is eroded Cathode Shinning brown substance deposit Copper is formed Colour of electrolyte Remain the same. Concentration of Cu2+ remains

Discussion:

	►	Electrolysis of copper(II) sulphate solution by using carbon electrodes Aqueous solution At anode(+) At cathode(-) Movements of ion to electrode SO42-, OH- CU2+, H+ Ion selected for discharged Ion OH- selected for discharged as it is lower position in electrochemical series. Ion Cu2+ selected for discharged as it is lower position in electrochemical series. Half-equation 4OH- →2H2O + O2 + 4e- Oxygen gas is collected. Cu2+ + 2e- → Cu Copper metal is deposited.
	►	Electrolysis of copper(II) sulphate solution by using copper electrodes Aqueous solution At anode(+) At cathode(-) Movements of ion to electrode SO42-, OH- Cu2+, H+ Ion selected for discharged Copper electrode ionizes to form Cu2+ Ion Cu2+ selected for discharged as it is lower position in electrochemical series. Half-equation Cu → Cu2+ + 2e- Copper electrode dissolve and its weight decrease. Cu2+ + 2e- → Cu Copper metal is deposited. Copper ionizes at the anode, and Cu2+ ions are discharged at the cathode. Thus, the concentration Cu2+ ions remain unchanged.

Conclusion:

	►	Different electrodes used in electrolysis lead to different product at the anode and at the cathode.
	►	The hypothesis is accepted.

↶ 6.3 Electrolysis of aqueous solutions

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