1) Electrolysis of molten compounds involves passing an electric current through a molten compound, causing its ions to migrate to the electrodes. 2) During electrolysis of molten lead(II) bromide (PbBr2), the Pb2+ ions migrate to the cathode, where they gain electrons and deposit as metallic lead. Meanwhile, the Br- ions migrate to the anode, where they lose electrons and form a bromine gas product. 3) The overall reaction is the decomposition of PbBr2 into lead metal and bromine gas.

1. ELECTROCHEMISTRYElectrolysis of molten compounds30/06/2010

2. At the end of the lesson, you should able to:describe electrolysis,describe electrolytic cell,identify cations and anions in a molten compound,describe evidence for the existence of ions held in a lattice in solid state but move freely in molten state,describe electrolysis of a molten compound,write half-equations for the discharge of ions at anode and cathode,predict products of the electrolysis of molten compounds.Learning outcomes

3. Video cliphttp://www.youtube.com/watch?v=i9xS9t-KMpc

4. Electrolysis of a molten compoundDescribe + diagramANODECATHODE

5. Electrolysis of molten PbBr2Molten lead (II) bromide, PbBr2 consists of Pb2+ ions and Br- ions that move freely.During electrolysis of molten lead (II) bromide, PbBr2 , the cations, Pb2+ ions move to the cathode; the anions, Br-ionsmove to theanode.

6. At CATHODE, Lead (II) ions , Pb2+ ions are discharged by receiving electrons to form Pb atom.Silvery grey solid is deposited at cathode.Lead, Pb metal is formed at the cathode.At cathode / anode,? ions are discharged, by receiving / donating (how many) electrons?Half equation?Observations?Products?Pb2+ (l) + 2 e- -> Pb (s)

7. At cathode / anode,? ions are discharged, by receiving / donating (how many) electrons?Half equation?Observations?Products?At ANODE, bromide ions , Br- are discharged by donating electrons to form Br2 molecules.Brown vapour is released at anode.Thus, bromine gas, Br2 is released at the anode.2Br- (l) -> Br2(g) + 2 e-

8. Overall equation:Pb2+ (l) + 2e- -> Pb (s)2Br- (l) -> Br2(g) + 2e-Pb2+ (l) + 2Br- (l) -> Pb (s) + Br2(g)

9. Other examples…Molten potassium iodide, KIMolten copper (II) chloride, CuClMolten zinc chloride, ZnCl2Molten lead (II) oxide, PbO