Chapter 6B - Electrolytic Cell Design Features

• contains free moving ions that can either donate or accept protons • molten liquid or aqueous solution

• site of electrolysis • must be conductive • allow electrons to move in the external circuit

• defines polarity of electrodes • provides external source of electrons • acts as a pump • electron flow is in one direction only

Allows electrons to move in the external circuit.

• oxidation occurs at the anode • reduction occurs at the cathode • electrons flow through an external wire

• converts electrical energy to chemical energy • anode is positively charged • cathode is negatively charged • Non-spontaneous reaction • Does not require seperate half cells • Power supply is required

• positively charged • connected to the +ve terminal of power source • attracts anions in the electrolyte • positive terminal of DC source removes/pulls electrons from the electrode & forces oxidation

• negatively charged • connected to the negative terminal of the power supply, forcing/pushing electrons onto the electrode & forces reduction to occur • attracts cations in the electrolyte

• require high temperatures to melt the ionic compound • can be hazardous and expensive

• unreactive • added to molten electrolytes to reduce the melting point • make electrolyte safer and cheaper Note: can be the product of some reactions and may spontaneously react

• an inert electrode will not take part in the reaction • a metal electrode can undergo oxidation at the anode if it is the strongest reductant present.

• potential difference is greater than the spontaneous reverse reaction as energy is lost in the cell typically as heat (resistance in the wires)

• an electrolyte • two electrodes • a battery/powersupply

• nature of the electrolyte • nature of the electrodes • concentration of an aqueous electrolyte

• standard electrode potential values not reliable under non-standard conditions • solutions containing chloride ions, the reaction at anode will vary depending on the concentration of solution • higher concentration: Cl- are favoured

• process involving depositing a thin layer of one metal over another by electrolysis • decoration & surface protection • cathode: object that is to be plated • anode: made from the metal used for plating (or inert metal in some cases) • electrolyte: solution of the metal ion used for plating

• ions produced will compensate for ones being consumed at the cathode • electrolyte concentration won’t change

• when extracting a reactive metal from its ore, the ore needs to be melted to form a molten electrolyte • water is excluded as it is a stronger oxidant & would react in preference • an additive needs to be added to the electrolyte to lower the melting temperature • metal is removed to prevent reaction w/ O₂ (g) • graphite electrode at the anode reacts w/ O₂ gas to produce CO₂ • electrodes will need replacing from time to time

• electrolysis of concentrated brine solution (NaCl) • cathode: inert electrode 2Na+(aq)+2H2O(l)+2e-−→ 2NaOH(aq)+H2(g) OH- produced by the reduction of water combines with Na+ to produce NaOH • Anode: inert electrode 2Cl-(aq) → Cl2(g)+2e- • A semipermeable membrane seperate anode & cathode, only allowing sodium ions to pass through

A process of purifying metal extracted from its ore using electrolysis

• cathode: pure metal electrode • anode: impure metal electrode • electrolyte: solution of the ion of the metal which is being purified

• the impure sample metals that are stronger reductants will form ions in the solution • these ions will not react at the cathode as they are weaker oxidants than the analyte

• metals in the impure sample that are weaker reductants will form a sludge at the bottom of the cell