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)