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Equilibria Workshop.

Equilibria Workshop. LTx Wed 17 th Jan 2018. 5:00+pm till ++ Senior’s (and 18mo). K, Kc, Kp , Ka , (Kb), Kw, Kin , Ksp , Kpc , Kstab. E.g. (general case), For the reaction: a E + b F ⇌ c G + d H K= [ products ]  [ G ] c [H ] d [ reactants ] [ E ] a [ F ] b.

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Equilibria Workshop.

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  1. Equilibria Workshop. LTx Wed 17th Jan 2018. 5:00+pm till ++Senior’s (and 18mo)

  2. K, Kc, Kp, Ka, (Kb), Kw, Kin, Ksp, Kpc, Kstab E.g. (general case), For the reaction: aE + bF⇌cG + dH K= [ products ] [ G ]c[H ]d • [ reactants ] [ E ]a[ F ] b Note: Show theEquilibrium sign

  3. To H2O or not to H2O. That is the question! • In aqueous systems, i.e. water acts as a solvent and is therefore present in large, effectively unchanging quantities…then WATER IS NOT INCLUDED in ‘named’ K equations. • However, when waternot a solvent, i.e. it is a reactant or product, then it is included. E.g. • CH3COOH(l) + CH3CH2OH(l) ⇌ CH3COOCH2CH3 (l)+ H2O(l)

  4. Acid dissociation eqmconst Ka HA(aq)⇌ [ H+ ](aq) + [A-](aq) Ka = [ H+ ] [A-] [HA]

  5. Ka Rearranged expression 1 Take out the [A-] term Ka [HA] = [ H+ ] Ka = [ H+ ]2 [HA] Ka = [ H+ ] [A-] [HA] Ka [HA] = [ H+ ]2 - lg(Ka [HA] ) = - lg([ H+ ] ) - lg(Ka [HA] ) ½= pH - ½lg(Ka [HA] ) = pH Assumptions 1) [HA]eq = [HA]initial 2) [H+]from ionised [HA] only

  6. Ka Rearranged expression 2Leave the A- in Henderson HasselbalchBUFFER, ( ) pKa - lg [acid] = pH+ ] [ salt] Ka = [ H+ ] [ salt] [acid] Ka = [ H+ ] [A-] [HA] Ka x [acid ] = [ H+ ] [ salt] ( ) ( ) - lgKa x [acid] = - lg([ H+ ] ) [ salt] - lg(Ka)+ - lg [acid] = - lg([ H+ ]) [ salt]

  7. Definition: Buffer. A solution comprising of a large reservoir of both a weak acid and it’s salt, in approximate equal concentrations, capable of resistingchanges in pH upon small additions of acid or base.

  8. pH titration • Curves • Ensure you can show/calculate • INITIAL pH • Equivalence point • FINAL pH • Buffering region. • pKa (if weak acid)

  9. Polyprotic acids. (substances that can lose 2 or more protons. H2CO3, H2SO4, H2SO3, etc.MULTIPLE EQUIVALENCE POINTS

  10. KapKa If pKa 1 thena weak acid. ………………………………………………………………………………………………………………………………..…. ………………………………………………………………………………………………………………………………..…. ………………………………………………………………………………………………………………………………..…. http://www2.ucdsb.on.ca/tiss/stretton/database/polyprotic_acids.htm

  11. Strong acids protonate weaker acids !!

  12. Ksp - Solubility product for SPARINGLY SOLUBLE SALTS (solubility  3.3g per 100ml)

  13. Do be careful! Make sure you put CONCENTRATIONS in, and not just moles. (divide moles by volume of the particular solvent) Do this even if the volumes of each solvent are the same. Can work in g/vol. Kpc is unitless. So state “unitless”

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