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 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 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 C(s) 0 5.6 CO2(g) -393.5 213 -394.4 Reaction with C: 2 Fe2O3(s) + 3 C(s)  4 Fe(s) + 3 CO2(g) 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 Production 2 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

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 Chemistry Fixing: AgX(s) + 2 Na2S2O3(aq)  Na3[Ag(S2O3)2](aq) + X-(aq)