Unit 4 - Electrochemistry

The breakdown of an ionic compound, molten or in aqueous solution by the passage of electricity in an electrolytic cell

Negative terminal of the battery

Positive terminal of the battery

• Battery • Two electrodes - one connected to the cathode as the negative electrode and another connected to the anode as the positive electrode • Electrolyte - aqueous or molten substance that conducts electricity

Substance being broken down - usually an ionic compound that is molten or aqueous

Carbon/platinum/graphite to be inert and good conductors of electricity

1.Electrolyte is made molten or dissolved in water to become aqueous 2.Electric current in passed through the cell 3.Cations move towards the cathode 4.Anions move towards the anode 5.Cations come from metal ions, gains an electron 6.Anions come from non-metal ions, loses an electron

1.Electrons flow from negative terminal of the battery to charge up the cathode 2. Attracts cations and makes them move toward the cathode to gain electrons (reduction) 3.Anions move toward anode and lose electrons (oxidation) 4.Electrons flow from the anode to the cathode

Process of making ions by either gaining or losing electrons

Compounds splitting to form ions - usually acids

-Cations below hydrogen on reactivity series will be reduced over the H+ ions and metal will form - Cations above hydrogen on reactivity series will cause H+ ions to be reduced, hydrogen gas will form and the metal ion with stay in solution

The electrochemical series

• Halide ions will form at the anode e.g. Cl- or Br- • Other negative ions e.g. SO4- will form oxygen from dissociation of OH- ions since sulfate is more reactive than hydroxide ions

• Cathode (-)= Pb^2+(1) + 2e^- –> Pb(s) • Anode (+)= 2Br^-(aq) –> Br2(g) + 2e^-

• Cathode (-)= 2H^+(aq) + 2e^- –> H2(g) • Anode (+)= 2Cl^-(aq) –> Cl2(g) + 2e^-

• Cathode (-)= 2H^+(aq) + 2e^- –> H2(g) • Anode (+)= 40H^-(aq) –> 2H2O(1) + O2(g) + 4e^-

Electrons are on the left hand side

Electrons are on the right-hand side

• Electroplating • Purification of copper/refining copper • Electrolysis of concentrated sodium chloride/brine

Coating one metal with a thin layer of another metal either to improve appearance or prevent corrosion

The object to be electroplated is made at the cathode and the anode is made from the metal that will be the coating layer

• Cathode (-)= Ag^+(aq) + e^- –> Ag(s) • Anode (+)= Ag(s) –> Ag^+(aq) + e^-

Electrolysis is used to get 99.9% copper to use in electrical wiring

1.At the anode copper atoms lose electrons and go as copper (II) ions in the solution: Cu(s) –> Cu^2+(aq) + 2e^- 2.Cu^2+ ions are attracted to the cathode to gain electrons and form copper atoms: Cu^2+(aq) + 2e^- –> Cu(s) - layer of pure copper build up on cathode 3.Platinum, silver and gold might have been present in the impure copper anode and drop to the bottom to make a mixture - slime 4.Anode loses mass and cathode gains mass