(ES) - Redox

• Electrolysis is the breaking down of a substance using electricity
• Can be conducted using ionic compounds that are either molten or dissolved in solution
• Ions need to be free to move around to conduct electricity
• Metallic bonding and graphite can conduct electricity due to free-moving electrons
• Graphite can be used in electrolysis for electrodes
• Two electrodes in electrolysis: Anode (positive electrode) and Cathode (negative electrode)
• Anions (negative ions) are attracted to the Anode and give up electrons
• Cations (positive ions) are attracted to the Cathode and receive electrons
• Electrodes must be made from inert conductive materials like platinum or graphite
• Electrodes are dipped into the electrolyte but must not touch
• Substances collect at the electrodes during electrolysis
• Solids plate the electrode and bubbles indicate gas production
• Reactions at each electrode can be shown using half equations
• Electrolysis of molten substances produces elements that make up the ionic compounds
• Example: Electrolysis of molten sodium chloride produces sodium and chlorine gas
• Electrolysis of aqueous solutions is more complex due to extra ions like OH- and H+
• Products formed at each electrode depend on ion reactivity and salt solution concentration
• At the Cathode: Less reactive metals than hydrogen form metal, more reactive form hydrogen gas
• At the Anode: Oxygen is formed if no halide ions present, halogen formed if halide ions present
• Halogen formed depends on salt solution concentration (dilute = oxygen, concentrated = halogen)
• Electrolysis can be used to purify metals like copper
• Impure copper at the Anode loses electrons and dissolves into the solution
• Pure copper at the Cathode gains electrons and plates the electrode
• Electrolysis of brine can extract halogens like chlorine
• Brine is a high concentration solution of salts found in seawater
• At the Cathode: H+ ions form hydrogen gas
• At the Anode: Cl- ions form chlorine gas, remaining ions react with hydroxide ions to form sodium hydroxide
• Electrodes can be platinum or graphite, must be inert
• Sodium chloride solutions must be concentrated to obtain chlorine via electrolysis
• Dilute solutions form oxygen instead of halogens
• Extraction of bromine and iodine using displacement reactions
• More reactive halogens like chlorine can extract bromine from brine
• Bromine is produced, condensed, and purified into a liquid
• Bromine is formed from bromide ions through a displacement reaction
• Bromine exists as a vapor when vaporized and condenses back into a liquid at room temperature
• Iodine can be extracted from its brine using a more reactive halogen, such as chlorine
• Chlorine is more reactive than iodine and can displace iodine through a displacement reaction
• Redox reactions involve the transfer of electrons between species
• Oxidation is the loss of electrons, while reduction is the gain of electrons
• OIL-RIG acronym: Oxidation Is Loss, Reduction Is Gain