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Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry , 2007 (John Wiley)      ISBN: 9 78047081 0866 . CHEM1002 [Part 2]. A/Prof Adam Bridgeman (Series 1) Dr Feike Dijkstra (Series 2) Weeks 8 – 13

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  1. Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille,Chemistry, 2007 (John Wiley)     ISBN: 9 78047081 0866

  2. CHEM1002 [Part 2] A/Prof Adam Bridgeman (Series 1) Dr FeikeDijkstra (Series 2) Weeks 8 – 13 Office Hours: Monday 2-3, Friday 1-2 Room: 543a e-mail:adam.bridgeman@sydney.edu.au e-mail:feike.dijkstra@sydney.edu.au

  3. Acids and Bases • Lecture 1: • Common Acids and • Bases • Definitions • Equilibria • Conjugate acid-base pairs • Autoionisation of water • pH • Blackman Chapter 11, Sections 11.1-11.3 Reproduced from ‘The Extraordinary Chemistry of Ordinary Things, C.H. Snyder, Wiley, 2002(Page 245)

  4. Use of Common Acids and Bases Substance Formula Use Acids Acetic acid CH3COOH flavouring; preservative Citric acid C6H8O7 flavouring Phosphoric acid H3PO4 rust remover Boric acid B(OH)3 mild antiseptic; insecticide Hydrochloric acid HClbrick/ceramic tile cleaner Bases Sodium hydroxide NaOH oven cleaner Ammonia NH3 household cleaner Sodium carbonate Na2CO3 water softener; grease remover Sodium hydrogen NaHCO3 fire extinguisher; baking powder carbonate Reproduced from ‘The Extraordinary Chemistry of Ordinary Things, C.H. Snyder, Wiley, 2002 (Page 231)

  5. Arrhenius:H+(aq) + OH-(aq)H2O(l) ACID: H+ producer in aqueous solution e.g. HCl BASE: OH- producer e.g. NaOH Brønsted - Lowry:H+ + A- HA ACID: proton donor (H+) e.g. HCl BASE: proton acceptor e.g. NH3 Definitions

  6. A STRONG acid has equilibrium to the right(HA completely ionised) A WEAK acid has equilibrium to the left(HA partly/mostly intact) Acids, Bases & Equilibrium HA(aq)+ H2O(l)H3O+(aq)+A-(aq) • Equilibrium Equation: • Kais the ACID DISSOCIATION CONSTANT

  7. NH4+ is the conjugate acid of NH3 NH3 is the conjugate base of NH4+ A conjugate base has one less proton than its conjugate acid HSO4–: conjugate base is SO42– conjugate acid is H2SO4 H2SO4 is a dibasic or diprotic acid: Conjugate Acid-Base Pairs H2SO4(aq) + H2O(l) H3O+(aq) + HSO4–(aq) HSO4–(aq) + H2O(l) H3O+(aq) + SO42–(aq)

  8. Acid-Base Reactions conjugate pair ACID + BASE BASE + ACID conjugate pair HF(aq)+ H2O(l) HCOOH(aq) + CN-(aq) H2PO4-(aq) + OH-(aq) NH4+(aq) + CO32-(aq) F-(aq) + H3O+(aq) HCOO-(aq) + HCN(aq) HPO42-(aq) + H2O(l) NH3(aq) + HCO3-(aq)

  9. Equilibrium constant given special symbol: Kw = [H3O+][OH– ] NB: [H2O(l)] = constant At 25 °C: Kw = 1.0  10-14 Neutral solution: [H+] = [OH– ] = 1.0  10-7 M Acidic solution: [H+] > 1.0  10-7 M Basic:[H+] < 1.0  10-7 M 2 H2O(l) H3O+(aq) + OH–(aq) remember this Autoionisation of Water

  10. The pH Scale Because the concentrations of acids and bases can vary over many orders of magnitude, it is convenient to define a logarithmic scale to compare them: pH= -log10[H+] pOH= -log10[OH-] pH + pOH = 14 e.g. If [H+] = 1.0 x 10-6 M then pH = -log(10-6) = - (-6) = 6.00 Hence, pOH = 14.00 – 6.00 = 8.00 and [OH-] = 10-8.00

  11. pH = – log10[H+] pOH = – log10[OH– ] pKw = – log10Kw = 14.00 at 25 °C The ‘p’ Convention • Acid : pH < 7 • Neutral: pH = 7 • Basic: pH > 7 • pH + pOH = 14 • pOH = 14 – pH Since Kw = [H+][OH– ]: log10Kw = log10 [H+] + log10 [OH– ] – log10 [H+] – log10 [OH– ] = – log10Kw

  12. Kw = 1.0  10-14only at 25 °C Reaction is endothermic: it is more favourable at higher temperature For T > 25 °C,Kw > 10-14 For T < 25 °C,Kw < 10-14 H++ OH- Ea H2O ΔH0 = 56 kJ mol-1 Temperature Dependence of pH  pH + pOH  14 if T  25 °C  neutral pH  7 if T  25 °C !

  13. [H+] pH 1 M NaOH 10-14 14 10-12 12 BASIC Household Ammonia 10-10 10 } Sea Water 10-8 8 Blood Pure Water NEUTRAL Milk 10-6 6 10-4 4 Vinegar Lemon Juice 2 10-2 ACIDIC Stomach Acid 1 M HCl 100 0

  14. Practice Examples • 1. Calculate the pH for solutions with each of the [H+(aq)] concentrations below • (a) 10.0 M • (b) 1.00 M • (c) 0.10 M • (d) 0.010 M • 2. Calculate the pH for solutions with each of the [OH-(aq)] concentrations below • (a) 10.0 M • (b) 1.00 M • (c) 0.10 M • (d) 0.010 M

  15. Summary: Acids & Bases 1 • Learning Outcomes - you should now be able to: • Complete the worksheet • List common acids and bases • Define acids & bases • Use pH and Kw • Answer Review Problems 11.1-11.11 and 11.128 in Blackman • Next lecture: • Calculations involving acids and bases

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