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 Decomposition Reaction: 2 Fe 2 O 3 (s)  4 Fe(s) + 3 O 2 (g)  H o =  S o =  G o = Temperature where  G o is negative?

Consider the reaction of Fe 2 O 3 with C Reaction with C: 2 Fe 2 O 3 (s) + 3 C(s)  4 Fe(s) + 3 CO 2 (g) C(s) CO2(g)  H o =  S o =  G o = Temperature where  G o is negative?

Consider the decomposition of HgO 2 HgO(s)  2 Hg(l) + O 2 (g)

Aluminum Production 2 Al 2 O 3 (dissolved) + C(s)  4 Al(l) + 3 CO 2 (g)

Aluminum Production 2 Al 2 O 3 (dissolved) + C(s)  4 Al(l) + 3 CO 2 (g) Why use carbon instead of just a metal electrode?  G o 2 Al 2 O 3 (s)  4 Al(s) + 3 O 2 (g) = kJ/mol E o =  G o 2 Al 2 O 3 (s) + 3 C(s)  4 Al(s) + 3 CO 2 (g) = kJ/mol E o =

Gold! 4 Au(s) + 8 NaCN(aq) + O 2 (g) + 2 H 2 O(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 Na 2 S 2 O 3 (aq)  Na 3 [Ag(S 2 O 3 ) 2 ](aq) + X - (aq)

Photography Chemistry