Electrochemistry: notes

Electrolysis

• Electrolyte: an ionic compound, molten or dissolved, whose ions carry current. Insulators and solid ionic compounds do not conduct.
• Electrolysis: breaking down a compound with direct current. Negative ions go to the anode (positive) and positive ions go to the cathode (negative).
• Molten lead(II) bromide: lead at the cathode, bromine at the anode.
• Copper(II) sulfate solution, carbon electrodes: copper at the cathode, oxygen at the anode.
• Brine: hydrogen at the cathode, chlorine at the anode.

Uses of Electrolysis

• Electroplating: the object is the cathode, the plating metal is the anode, and the electrolyte contains ions of that metal. A spoon is silver plated in silver nitrate solution.
• Purifying copper: impure copper is the anode and pure copper is the cathode, in copper(II) sulfate. Copper dissolves from the anode and deposits on the cathode.
• Extracting aluminium: aluminium oxide dissolved in molten cryolite. Aluminium forms at the cathode and oxygen at the carbon anodes, which burn away and must be replaced.

Cells

• Simple cell: two different metals in an electrolyte. The more reactive metal is the negative terminal, so zinc with copper sends electrons through the wire to copper.
• Hydrogen fuel cell: hydrogen and oxygen react to give water and electricity, with no polluting gas.