4. Electrochemistry

• Define electrolysis as the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current

• Identify in simple electrolytic cells: (a) the anode as the positive electrode (b) the cathode as the negative electrode (c) the electrolyte as the molten or aqueous substance that undergoes electrolysis

• Describe transfer of charge during electrolysis to include: (a) the movement of electrons in the external circuit (b) the loss or gain of electrons at the electrodes (c) the movement of ions in the electrolyte

• Identify products and observations during electrolysis of: (a) molten lead(II) bromide (b) concentrated aqueous sodium chloride (c) dilute sulfuric acid with inert platinum/carbon electrodes

• State: metals or hydrogen are formed at the cathode and that non-metals (other than hydrogen) are formed at the anode

• Predict the identity of the products at each electrode for the electrolysis of a binary compound in the molten state

• State: metal objects are electroplated to improve their appearance and resistance to corrosion

• Describe how metals are electroplated

• Identify the products formed at the electrodes and describe the observations made during the electrolysis of aqueous copper(II) sulfate using inert carbon/graphite electrodes and when using copper electrodes

• Predict the identity of the products at each electrode for the electrolysis of a halide compound in dilute or concentrated aqueous solution

• Construct ionic half-equations for reactions at the anode (to show oxidation) and at the cathode (to show reduction)

4.2.1Hydrogen–oxygen fuel cell uses

• State: a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product

4.2.2Advantages and disadvantages of using

• Describe advantages and disadvantages of using hydrogen–oxygen fuel cells in comparison with gasoline/petrol engines in vehicles