Extraction of Pure Elements from Nature

Which elements are easy?

Easy elements are gases that exist in the elemental form

N2, O2, 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: Fe2O3 has Fe3+ ions. To obtain Fe metal, need to add 3 electrons to each Fe3+ ion.

What we’ll find.

Review of Thermodynamic Control of Reactions

is negative, then the reaction is favored

o o o

o

G H T S

If G

Enthalpy: H depends on bond strengthreactions 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 Fe2O3

Decomposition Reaction: 2 Fe2O3(s) 4 Fe(s) + 3 O2(g)

Ho =

So =

Go =

Temperature where Go is negative?

Consider the reaction of Fe2O3 with C

Reaction with C: 2 Fe2O3(s) + 3 C(s) 4 Fe(s) + 3 CO2(g)

C(s) 0 5.6

CO2(g) -393.5 213 -394.4

Ho =

So =

Go =

Temperature where Go is negative?

Consider the decomposition of HgO

2 HgO(s) 2 Hg(l) + O2(g)

Aluminum Production

2 Al2O3(dissolved) + C(s) 4 Al(l) + 3 CO2(g)

Aluminum Production2 Al2O3(dissolved) + C(s) 4 Al(l) + 3 CO2(g)

Why use carbon instead of just a metal electrode?

Go 2 Al2O3(s) 4 Al(s) + 3 O2(g) = + 3164 kJ/mol

Eo =

Go 2 Al2O3(s) + 3 C(s) 4 Al(s) + 3 CO2(g) = + 1981 kJ/mol

Eo =

Gold!4 Au(s) + 8 NaCN(aq) + O2(g) + 2 H2O(l) 4 NaAu(CN)2(aq) + 4 NaOH(aq)

Photography Chemistry

Exposure: AgX Ag(s) + X(s)

Photography Chemistry

Developing: AgX(s) + e- Ag(s) + X-(s) HQ Q + 2 H+ + 2e-

Photography ChemistryFixing: AgX(s) + 2 Na2S2O3(aq) Na3[Ag(S2O3)2](aq) + X-(aq)

Photography Chemistry