C3.4 Electrolysis

Process where electric current is passed through a compound causing a chemical change Also splits ionic compounds Electrolyte - compound in its liquid state or in solution that can conduct electricity and contains mobile ions 2 electrodes made form metal or graphite to conduct electricity to the electrolyte: Negative cathode Positive anode Electrical supply such as a power pack or battery

Cathode

Anode

Gain electrons at cathode and become atoms

Lose electrons at anode and become atoms

Covalent bonds will form between them, making molecules

Cations

Anions

Contains only 2 elements

When ions become atoms or molecules at an electrode

Don’t change during electrolysis Made from unreactive metals such as copper and platinum, or graphite Used for many ionic compounds in their liquid state or aqueous solution

H2O(l) ⇌ H+(aq) + OH-(aq) Hydrogen ions discharged at cathode, in gas state Hydroxide ions discharged at the anode, forming water and oxygen in its gas state

Type of electolysis that uses non inert electrodes They change during the electrolysis Anode loses mass Cathode gains mass

The object to coat

Piece of the metal to coat with

Solution containing ions of the coating metal

Both electrodes made from the same metal Anode: impure metal Cathode: very pure metal Cathode gains metal atoms and increases in mass Anode loses metal atoms and reduces in mass Impurities collect under the anode

Compound is split up Positive ion attracted to negative electrode Negative ion attracted to positive electrode Ions are discharged at the electrodes - become atoms Bunsen burner needed Might not be used as high amount of energy needed in order to get the compound in the molten state.

At the Cathode (-) Least reactive ion discharged (often hydrogen) Link to reactivity series At the Anode (+) If halide present, it will be discharged and a halogen is formed If no halide, then oxygen given off ONLY 1 ION CAN BE DISCHARGED AT AN ELECTRODE

Potassium. Sodium. Calcium. Magnesium. Aluminium. (Carbon). Zinc. Iron. Tin. Lead. (Hydrogen). Copper. Silver. Gold Platinum Most reactive. Least reactive Please Stop Calling Me A Careless Zebra Instead Try Learning HoW Copper Saves Gold Platinum

Reduction - cathode (red-cat) Oxidisation - anode

Lead bromide: Anode reaction: 2Br- —> Br2 + 2e- : bromine (non metal) is produced Cathode reaction: Pb²+ + 2e- —> Pb : lead (metal) is produced (Molten electrolysis) Sodium chloride: Anode Reaction: 2Cl- —> Cl2 + 2e- Cathode Reaction: 2H+ + 2e- —> H2 (Aqueous electrolysis) Remember format of half equations for anode and cathode. NB: THESE QUESTIONS CAN BE VERY UNPREDICTABLE AND ARE ONLY 1 OR 2 MARKS IN A TEST. THERE IS NO CLEAR WAY AND WE WERE NOT CLEARLY TAUGHT.

Anode: 2Cl- —> Cl2 + 2e- Cathode: Cu 2+ + 2e- —> Cu

Anode: 2Cl- -> Cl2 + 2e- Cathode: 2H+ + 2e- -> H2