6.3.1 - Laboratoty Activity : Positions of ions in the electrochemical series

Laboratory Activity 6.3.1: Positions of ions in the electrochemical series

Aim: To study the effect of the position of ions in the electrochemical series on the products of electrolysis
Problem statement: How does the position of ions in the electrochemical series influence the choice of ion for discharge?
Hypothesis: Ion located at the lower position in the electrochemical series will be preferably discharged at the electrode.
Variable:

	»	Fixed variable : Concentration of electrolytes and types of electrodes
	»	Manipulated variable : Position of ions in the electrochemical series
	»	Responding variable : Types of ions discharged at the anode and the cathode

Material: » Dilute sulphuric acid » Copper(II) sulphate solution

Apparatus: » Electrolytic cell » Test tube » Carbon 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 acid for 15 minutes. 2. The gases collected at the electrodes are tested, and observation are recorded. 3. The acid is replaced with copper(II) sulphate.

Results:

	►	Dilute sulphuric acid Electrode Observation Inference Anode Colourless gas released. Light up glowing splinter. Oxygen gas is released. Cathode Colourless gas released. Give a 'pop' sound with burning splinter. Hydrogen gas is released
	►	Copper(II) sulphate solution 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

Discussion:

	►	Dilute sulphuric acid Aqueous solution At anode(+) At cathode(-) Movements of ion to electrode SO42-, OH- H+ Ion selected for discharged Ion OH- selected for discharged as it is lower position in electrochemical series. Ion H+ selected for discharged as it is lower position in electrochemical series. Half-equation 4OH- →2H2O + O2 + 4e- Oxygen gas is collected. 2H+ + 2e- → H2 Hydrogen gas is collected.
	►	Copper(II) sulphate solution 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.

Conclusion:

	►	The position of ions in the electrochemical series influences the ions selected for discharge at the electrodes. Thus, the electrolysis of ○ dilute sulphuric acid produces hydrogen gas at the cathode and oxygen gas at the anode. ○ copper(II) sulphate solution produces copper at the cathode and oxygen at the anode.
	►	The hypothesis is accepted.

↶ 6.3 Electrolysis of aqueous solutions

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