unit 2 b notes metal uses redox 08 09
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Unit 2B
Earth’s Mineral Resources
Metal Uses
Humans – toolmakers
Stone Age stone and copper tools first
made 10,000 yrs ago Unreactive native metals
used to make coins, decorative objects, some tools (esp. Cu)
Metal Uses
Bronze Age began 3800 BC alloy of tin and copper
Metal Uses
Iron Age began 1000 BC man discovered fire can
be used to separate iron from iron ore
Additional metals removed from ores
Worthwhile to mine a metal?
Consider amt of useful ore at the
site % of metal in the ore type of mining and
processing needed to extract the metal from its ore
Worthwhile to mine a metal?
distance of mine from metal refining facility and markets
metal’s supply-vs-demand
Metal Reactivity
How readily a certain metal reacts with oxygen provides information about the metal’s reactivity.
If elements are ranked in relative order of their chemical reactivity, the ranking is called an activity series.
Metal Reactivity
If copper is heated in air, it will react w/ oxygen to produce a black substance:
2 Cu(s) + O2 (g) 2 CuO(s)
Copper + Oxygen Copper(II) oxide
Metal ReactivityHowever, magnesium will react w/ oxygen
when heated by igniting and releasing brilliant light:
2 Mg(s) + O2(g) 2 MgO(s)
Magnesium + Oxygen Magnesium oxide
Metal Reactivity
Gold does not react with oxygen (even at high T)
Durable, long-lasting Suitable for use in
jewelry, electronics
Metal Reactivity most reactive
metallic elements are at the top;
less reactive elements are closer to the bottom.
Refining Metals
Metal reactivity generally decreases from left – right on periodic table
If Metal X is listed above Metal Y in an activity series, then Metal X will react (reduce) with Metal Y in solution
Refining Metals
Ores generally contain metals in ionic form (cations), these cations need to be combined with electrons in a chemical reaction to obtain useful neutral metal atoms
Refining Metals
Reduction reactions – any chemical change in which a cation gains electrons
Cu2+ + 2e- Cu (metal)
Oxidation reactions – any reaction in which atoms lose electrons
Cu (metal) Cu2+ + 2e-
Refining Metals
To gain electrons, chemists must “supply” electrons from atoms that readily lose electrons
Oxidation and reduction reactions must occur simultaneously, therefore we group them together and call them Redox reactions
Refining Metals
Cu (s) + 2Ag+ (aq) Cu2+ (aq) + Ag (s)
Copper was oxidized (converted to Cu2+ by losing two electrons
Each silver ion was reduced (converted to a silver atom by gaining one
electron)
Cu2+ (aq) + Mg (s) Cu (s) + Mg2+ (aq)
Magnesium atoms are oxidized Copper ions are reduced The reducing agent is Magnesium (source
of electrons for the metal being obtained) Total electrical charges and atoms must
balance on each side of the reaction – Why?
Refining MetalsLEO the lion goes GER
Loses Electrons = Oxidation
Gains Electrons = Reduction
Obtaining metals from ores requires:energy and a reducing agent
Refining Metals
Electrometallurgy uses an electric current to serve as a reducing agent Used when pure metal is needed or no
suitable aqueous reducing agent is available
Refining Metals
Pyrometallurgy uses heat (furnaces) or more reactive metals to reduce metal ores Oldest method, most widely used method
Refining Metals
Hydrometallurgy – reduction of metal ions from ores in aqueous solutions (leaching) May be used to obtain metals from old
“tailings” (leftover rock from previous ore processing)