Topic 19.1 - Electrolysis

Made from an unreactive metal (platinum etc.) or graphite. These are not changed during electrolysis.

Occurs in sulfuric acid (H₂SO₄) or sodium hydroxide (NaOH) using inert platinum (Pt) electrodes H⁺ ions are discharged at the cathode to form hydrogen gas (2H⁺ (aq) + 2e⁻ -> H₂ (g)) OH⁻ ions are discharged at the anode to form water and oxygen gas (4OH⁻ (aq) - 4e⁻ -> 2H₂O (l) + O₂ (g))

Contains the ions of the solute, hydrogen ions (H⁺), and hydroxide ions (OH⁻). Hydrogen ions (H⁺) will discharge at the cathode unless a less reactive metal is present (Sb, As, Bi, Cu, Ag, Pd, Hg, Pt, Au) hydroxide ions (OH⁻) will discharge at the anode unless halogen ions (excluding fluoride ions (F⁻)) are present in high concentrations.

The electrode potential of a redox system to lose or gain electrons when compared to the SHE. More positive standard electrode potential - preferred product for reactions at the anode, more negative standard electrode potential for reactions at the cathode.

Galvanising

Type of electrolysis where an object is coated in a thin layer of metal. Cathode - negative electrode, contains the original metal which you want to have electroplated Anode - positive electrode containing the metal you want to use to electroplate Electrolyte - Ions of the metal that you are using to electroplate (usually with H₂SO₄²⁻ or NO₃⁻ anions )

Generates an electromotive force (EMF) resulting in the movement of electrons from the anode (-) to the cathode (-) via the external circuit.

Electromotive force is the standard cell potential value (E^⦵) and the value is determined under standard conditions: 298K, 1 mol dm⁻³, 100kPa

Standard electrode potential. The potential voltage of the reduction relative to the SHE. E^⦵ꜜcell = E^⦵ꜜred - E^⦵ꜜox

More positive E⦵ value is on the right (cathode). Cu²⁺ + 2e⁻ ⇌ Cu (E⦵ = +0.34V) Zn²⁺ + 2e⁻ ⇌ Zn (E⦵ = -0.76V) Zn ⋮ Zn²⁺ ll Cu²⁺ ⋮ Cu

Standard hydrogen electrode. Consists of an inert platinum electrode in contact with 1 mol dm⁻³ hydrogen ion and hydrogen gas at 100kPa and 298K.

If E^⦵ꜜcell is positive, the redox reaction will be spontaneous. Gibbs free energy is negative if it’s spontaneous, ΔG = -nFE^⦵ꜜcell

F = charge in coloumbs of 1 mole of electrons (Faradays constant (in DB)) n = amount in moles (moles of electrons transferred) E^⦵ꜜcell = standard electrode potential (V of cell)