Activity 01
Electrolysis of Water (Hoffman Voltameter Demo)
Set up a Hoffman voltameter with dilute sulfuric acid to demonstrate the decomposition of water into hydrogen and oxygen gas. Students can observe the 2:1 volume ratio of gases produced and test for each gas using a lit splint (for H₂) and a glowing splint (for O₂).
Explain the difference between an electrochemical cell and an electrolytic cell.
Facilitation TipEnsure you clearly explain that the sulfuric acid is a catalyst and electrolyte, not a reactant, allowing current to flow.
What to look forUse mini-whiteboards for students to quickly write and display the predicted products and half-equations for the electrolysis of a given compound, allowing for instant feedback.
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Activity 02
Electroplating a 2c Coin
Students use a simple circuit with a power pack, a copper strip (anode), and a 2 cent coin (cathode) immersed in copper(II) sulfate solution. They will observe the coin becoming coated in a fresh layer of copper.
Analyse the factors that determine which ion is discharged at an electrode during the electrolysis of an aqueous solution.
Facilitation TipRemind students to thoroughly clean the coin with steel wool beforehand for a more even and effective plating.
What to look forAssign a past Leaving Certificate examination question on electrolysis. This will assess their ability to apply their knowledge to predict products, write equations, and explain the principles in an exam context.
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Activity 03
Predict and Test: Electrolysis of Aqueous Solutions
In small groups, students predict the products of electrolysis for various aqueous solutions (e.g., CuSO₄, KI, NaCl). They then perform the electrolysis on a small scale using carbon electrodes and test for the products, for example using universal indicator or starch solution.
Compare the products of electrolysis of molten sodium chloride and aqueous sodium chloride.
Facilitation TipProvide a printed electrochemical series to each group to guide their predictions before they begin the practical work.
What to look forProvide students with a checklist of skills for the topic (e.g., 'I can define electrolysis', 'I can predict the products for molten salts', 'I can use the electrochemical series for aqueous solutions'). Students rate their confidence level for each skill.
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Generate Complete Lesson→A few notes on teaching this unit
Begin by firmly establishing the contrast between electrochemical and electrolytic cells, focusing on the direction of energy flow. Use the electrochemical series as the central predictive tool, but explicitly teach the 'rules' for when water gets involved in aqueous solutions. Practical demonstrations, like electroplating a coin, are invaluable for making these abstract concepts tangible and memorable for students.
Upon completing these activities, students will be able to confidently predict the products of electrolysis in both molten and aqueous systems and justify their predictions using chemical principles.
Watch Out for These Misconceptions
Electrons flow through the electrolyte solution to complete the circuit.
Electrons do not travel through the electrolyte. Instead, mobile ions (cations and anions) move towards the oppositely charged electrodes, carrying the charge through the solution. Electrons only flow through the external circuit (the wires and power supply).
The anode is always the negative electrode.
This is only true for an electrochemical (voltaic) cell. In an electrolytic cell, the anode is the positive electrode because it is connected to the positive terminal of the external power supply. Oxidation always occurs at the anode in both types of cells.
In the electrolysis of an aqueous salt solution, only the ions from the salt are involved in the reaction.
Water molecules can also be oxidised (at the anode) or reduced (at the cathode). The actual product at each electrode depends on the relative positions of the ions and water in the electrochemical series and, in some cases, their concentration.
Methods used in this brief