Extraction of Pure Elements from Nature Which elements are easy?

Easy elements are gases that exist in the elemental form N 2, O 2, noble gases Obtained by distillation of cooled, liquified air.

Preview

Extraction of Metals All metals exist as cations in chemical compounds in the crust. Key: reducing the cations to the neutral metal. Example: Fe 2 O 3 has Fe 3+ ions. To obtain Fe metal, need to add 3 electrons to each Fe 3+ ion.

What we’ll find.

Review of Thermodynamic Control of Reactions Enthalpy:  H depends on bond strength reactions favored by negative  H (which is forming stronger bonds) Entropy:  S depends on randomness (disorder) reactions favored by positive  S (increasing disorder, particularly formation of gases)

Consider the decomposition of Fe 2 O 3

Consider the decomposition of HgO

Iron vs. Steel

Difficult-to-Reduce Metals: Electrolysis Aluminum

Difficult-to-Reduce Metals: Electrolysis Sodium

Rare, Native Metals: Gold Three Processes 1. Panning: Gold is dense 2. Mercury- historically important, but not now Pulverize rock, drench in liquid mercury; gold dissolves in Hg and is leached out. Then, boil off mercury to give gold 3. Cyanide Process Step 1: oxidative leaching: 4 Au(s) + 8 NaCN(aq) + O 2 (g) + 2 H 2 O(l)  4 NaAu(CN) 2 (aq) + 4 NaOH(aq) Step 2. Reduction and recovery 2 Au(CN) 2 - (aq) + Zn(s)  Zn 2+ (aq) + 4 CN - (aq) + 2 Au(s)

Nonmetals: Sulfur; Frasch Process

Difficult to Oxidize Nonmetals: Electrolysis, Chlorine