Extraction of Pure Elements from Nature

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Extraction of Pure Elements from Nature

• Which elements are easy?

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Easy elements are gases that exist in the
elemental form
N2, O2, noble gases Obtained by distillation of
cooled, liquified air.
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Preview
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Extraction of Metals
All metals exist as cations in chemical compounds
in the crust. Key reducing the cations to the
neutral metal. Example Fe2O3 has Fe3 ions. To
obtain Fe metal, need to add 3 electrons to each
Fe3 ion.
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What well find.
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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)
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Consider the decomposition of Fe2O3
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Consider the decomposition of HgO
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Consider the reaction of C Fe2O3
C 0
5.7 CO2
-393.5 213
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Iron vs. Steel
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Difficult-to-Reduce Metals Electrolysis Aluminum
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Cost of Aluminum Electrolysis 1 C 1 A?s 96485
C 1 mol e- 1 kWh 3.6 x 106 J 1 J 1
C?V Aluminum processed at 5.5 V.
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Why the Carbon Electrodes?
2 Al2O3(s) ? 4 Al(s) 3 O2(g)
?Go 3164 kJ 2 Al2O3(s) 3 C(s) ? 4
Al(s) 3 CO2(g) ?Go 1981 kJ
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Difficult-to-Reduce Metals Electrolysis Sodium
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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)
O2(g) 2 H2O(l) ? 4 NaAu(CN)2(aq) 4
NaOH(aq) Step 2. Reduction and recovery
2 Au(CN)2-(aq) Zn(s) ? Zn2(aq) 4 CN-(aq)
2 Au(s)
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Nonmetals Sulfur Frasch Process
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Difficult to Oxidize Nonmetals Electrolysis,
Chlorine
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