Presentation on theme: "1 Negative Ions - Bromine Negative ions are attracted to the positive electrode. The positive electrode is called the anode. Negative ions are called anions."— Presentation transcript:
1 Negative Ions - Bromine Negative ions are attracted to the positive electrode. The positive electrode is called the anode. Negative ions are called anions. Bromine ions are anions.
2 Electrolysis Of Molten Lead Bromide What are the products when molten lead bromide undergoes electrolysis? Bromine gas forms at the anode (negative bromine anions are attracted to the positive anode). The products are liquid lead and bromine gas. Liquid lead forms at the cathode (positive lead cations are attracted to the negative cathode). Half equation at the anode… 2Br - ( l) - 2e - Br 2(g) Half equation at the cathode… Pb 2 + (l) + 2e - Pb (l)
3 Electrolysis Of Potassium Nitrate Solution What are the products when potassium nitrate solution undergoes electrolysis? Oxygen gas forms at the anode. The products are oxygen gas and hydrogen gas. Hydrogen gas forms at the cathode. At the anode… 4OH - (aq) - 4e - 2H 2 O (l) + O 2(g) At the cathode… 2H + (aq) + 2e - H 2(g)
7 Extracting Aluminium - Cathode During the extraction of aluminium the positive aluminium ions (Al 3+ ) are attracted to the negative electrode. At the negative electrode (made of graphite) each aluminium ion gains three electrons. What is the half equation at the negative electrode (cathode)? Al 3+ (l) + 3e - Al (l) Molten aluminium forms at the graphite cathode. Bauxite (aluminium oxide) is an ore used in the extraction of aluminium. It is mixed with cryolite to lower its melting point (and thus save money).
8 Exercise: Extracting Aluminium 1.What are the electrodes made from in the extraction of aluminium from its ore? 2.What is the electrolyte used in the process? 3.To which electrode are the aluminium ions attracted? 4.How many electrons does each aluminium ion gain at this electrode? 5. What is the half-equation at the cathode? Graphite Cathode Al 3+ (l) + 3e - Al (l) Three Aluminium oxide and molten cryolite
9 Some Common Ores MetalOre Aluminium Iron Lead Sodium Calcium Potassium Magnesium Zinc Bauxite Haematite Galena Rock salt Limestone Silvine Magnesite Calamine
10 Roasting Galena Galena is an ore of lead, lead sulfide (PbS). Roasting galena: Lead sulfide (s) + oxygen (g) lead oxide (s) + sulfur dioxide (g) 2PbS (s) + 3O 2(g) 2PbO (s) + 2SO 2(g) If you roast galena in air, the oxygen in the air displaces the sulfur to form lead oxide. Heating the lead oxide with carbon: Lead oxide (l) + carbon (s) lead (s) + carbon dioxide (g) 2PbO (l) + C (s) 2Pb (s) + CO 2(g)
13 Exercise: Ionic Compounds 1.What sort of structures do ionic compounds form? 2. Name some ionic compounds. 3.What holds ionic compounds together? 4.Why do ionic compounds have high melting and boiling points? 5.Why will solid ionic compounds not conduct electricity? Giant ionic lattices The electrostatic attraction between oppositely charged ions The strong forces of electrostatic attraction between adjacent oppositely charged ions In solid ionic compounds the ions are not free to move, it is only when ionic compounds are aqueous or in the molten state that they will conduct electricity because then the ions are free to move Sodium chloride, magnesium oxide, calcium chloride
14 Fractional Distillation Crude oil is a mixture of various organic compounds. They are separated using the fact that the different compounds have different boiling points. To separate crude oil it is heated in a fractionating column and allowed to boil. The various compounds rise through the column and then recondense at different temperatures. The compounds recondense in different fractions. Each fraction contains molecules with a similar number of carbon atoms. As the number of carbon atoms increase in a molecule, the boiling point of the molecule also increases. The fractionating column is hottest at the base, so as you move up through the column and through the various fractions the number of carbon atoms in the molecules decreases.