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Flashcards · 0620 · Topic 4

Electrochemistry flashcards

14 cards on Topic 4, subtopics 4.1 to 4.2. Pick a subtopic or study them all.

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4.1 Electrolysis

Electrolysis
The decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
Anode and cathode
Anode: the positive electrode. Cathode: the negative electrode. (PANIC — Positive is Anode, Negative Is Cathode.)
Products of electrolysing molten lead(II) bromide with inert electrodes
Cathode: lead. Anode: bromine (red-brown vapour).
Products of electrolysing concentrated aqueous sodium chloride with inert electrodes
Cathode: hydrogen. Anode: chlorine.
Products of electrolysing dilute sulfuric acid with inert electrodes
Cathode: hydrogen. Anode: oxygen. Volume ratio hydrogen : oxygen = 2 : 1.
Electroplating: the cathode, the anode and the electrolyte
Cathode: the object to be plated. Anode: the plating metal. Electrolyte: a solution containing ions of the plating metal.
What happens at each electrode, in terms of electrons?Extended
Cathode: reduction — ions gain electrons. Anode: oxidation — ions lose electrons. (AN OIL RIG CAT)
Half-equations for electrolysing molten lead(II) bromideExtended
Cathode: Pb²⁺ + 2e⁻ → Pb Anode: 2Br⁻ → Br₂ + 2e⁻
Aqueous solution: which is discharged at the cathode, the metal or hydrogen?Extended
The less reactive of the two. A metal below hydrogen in the reactivity series (Cu, Ag) is deposited; otherwise hydrogen is given off.
Products of electrolysing dilute aqueous sodium chloride with inert electrodesExtended
Cathode: hydrogen. Anode: oxygen (the halide is not concentrated enough to be discharged).
Copper(II) sulfate solution electrolysed with copper electrodesExtended
Copper is deposited at the cathode. The copper anode dissolves (Cu → Cu²⁺ + 2e⁻) instead of oxygen being released.

4.2 Hydrogen–oxygen fuel cells

Hydrogen–oxygen fuel cell
Uses hydrogen and oxygen to produce electricity. The only product is water.
Advantages of a hydrogen fuel cell over a petrol engineExtended
Only water is produced, so no CO₂ at the point of use. More efficient than combustion.
Disadvantages of a hydrogen fuel cellExtended
Hydrogen is hard to store and transport, highly flammable and expensive, and producing it may itself release CO₂.

Revise Electrochemistry further