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neurologyYou need to know

• Electrolysis is the decomposition of an ionic compound, called an electrolyte, using direct current electricity.
• An electrolyte is a molten ionic compound or an ionic solution that contains mobile ions which can carry charge.
• Electricity is the flow of electric charge, usually carried by moving electrons in wires and moving ions in electrolytes.
• Ionic compounds must be molten or dissolved in water for electrolysis because their ions must be free to move to the electrodes.
• The cathode is the negative electrode in electrolysis and attracts positive ions, called cations.
• The anode is the positive electrode in electrolysis and attracts negative ions, called anions.
• During electrolysis, cations gain electrons at the cathode, so cathode reactions are reductions.
• During electrolysis, anions lose electrons at the anode, so anode reactions are oxidations.
• Oxidation is loss of electrons and reduction is gain of electrons.
• Metals more reactive than carbon are extracted by electrolysis, while many metals less reactive than carbon can be extracted by reduction with carbon or carbon monoxide.
• In molten electrolysis, the metal forms at the cathode and the non-metal forms at the anode.
• Aluminium is extracted by electrolysis of aluminium oxide dissolved in molten cryolite.
• Cryolite lowers the melting point of aluminium oxide, reducing the energy needed for aluminium extraction.
• In aluminium extraction, aluminium ions gain electrons at the cathode to form aluminium metal: `Al^{3+} + 3e^- \rightarrow Al`.
• In aluminium extraction, oxide ions lose electrons at the anode to form oxygen gas: `2O^{2-} \rightarrow O_2 + 4e^-`.
• The positive carbon anodes in aluminium extraction must be continually replaced because oxygen reacts with the hot carbon to form carbon dioxide.
• In aqueous electrolysis, hydrogen is produced at the cathode if the metal ion is from a metal more reactive than hydrogen.
• In aqueous electrolysis, the metal is produced at the cathode if the metal ion is from a metal less reactive than hydrogen.
• In aqueous electrolysis, oxygen is produced at the anode unless the solution contains halide ions.
• Halide ions are discharged at the anode in preference to hydroxide ions, producing chlorine, bromine, or iodine depending on the halide present.

• Identify the cathode and anode in an electrolysis cell by using the cathode as the negative electrode and the anode as the positive electrode.
• Explain why an ionic compound must be molten or dissolved before electrolysis by referring to mobile ions carrying charge.
• Classify electrode reactions as oxidation or reduction by checking whether electrons are lost or gained.
• Write balanced half equations for cathode reactions by showing positive ions gaining the correct number of electrons.
• Write balanced half equations for anode reactions by showing negative ions losing the correct number of electrons.
• Predict the product at the cathode in aqueous electrolysis by comparing the metal ion with hydrogen in the reactivity series.
• Predict the product at the anode in aqueous electrolysis by checking whether halide ions are present before predicting oxygen.
• Describe aluminium extraction by naming aluminium oxide, molten cryolite, the cathode product, the anode product, and the need to replace carbon anodes.
• Decide whether a metal should be extracted by electrolysis or reduction by comparing its position in the reactivity series with carbon.
• Predict the products of electrolysis for a named aqueous ionic compound by applying the cathode and anode discharge rules.