EJC 2023 Acid-Base Equilibria Lecture Notes (Students)

2023 JC1 H2 CHEMISTRY (9729) EXTENSION TOPIC: CHEMISTRY OF AQUEOUS SOLUTIONS TOPIC 8: ACID-BASE EQUILIBRIA Name: ___________________________________________ Civics Group: 23 – ____ REFERENCES 1. Chemistry (for CIE AS & A Level) by Peter Cann & Peter Hughes 540 CAN 2. Chemistry: The Molecular Nature of Matter & Change by Martin S. Silberberg 540 SIL 3. Calculations in A Level Chemistry (4th Edition) by E.N. Ramsden 540 RAM 4. Calculations for AS/A Level Chemistry by Jim Clark 540 CLA Learning Outcomes Students should be able to: (a) show understanding of and apply the Arrhenius theory of acids and bases (b) show understanding of and apply the Brønsted -Lowry theory of acids and bases, including the concept of conjugate acids and conjugate bases (c) show understanding of and apply the Lewis th eory of acids and bases (including non -aqueous system, e.g. reaction between BF3 and NH3) (d) explain qualitatively the differences in behaviour between strong and weak acids and bases in terms of the extent of dissociation (e) explain the terms pH; Ka; pKa; Kb; pKb; Kw and apply them in calculations, including the relationship Kw = KaKb (f) calculate [H +(aq)] and pH values for strong acids, weak monobasic (monoprotic) acids, strong bases, and weak monoacidic bases [Calculations involving weak acids/bases will not req uire solving of quadratic equations] (g) describe the changes in pH during acid-base titrations and explain these changes in terms of the strengths of the acids and bases (h) explain the choice of suitable indicators for acid-base titrations, given appropriate data (i) (i) explain how buffer solutions control pH (ii) describe and explain their uses, including the role of H2CO3/HCO – 3 in controlling pH in blood (j) calculate the pH of buffer solutions, given appropriate data

A c i d - B a s e E q u i l i b r i a P a g e | 2 E u n o i a J u n i o r C o l l e g e LECTURE CONTENT 1 Theories of Acids and Bases .................................................................................................... 3 1.1 The Three Theories of Acids and Bases ............................................................................ 4 1.2 The Hydrogen Ion ............................................................................................................... 5 2 Brønsted-Lowry Acids and Bases ............................................................................................ 8 2.1 Conjugate Acid-Base Pairs ................................................................................................. 8 2.2 Basicity or Proticity of Acids................................................................................................ 9 3 Water as Solvent ...................................................................................................................... 10 3.1 Levelling Effect of Water ................................................................................................... 10 3.2 Ionic Product of Water, Kw ................................................................................................ 10 3.3 pH and pOH ...................................................................................................................... 11 3.4 pH and Neutrality .............................................................................................................. 12 3.5 Strength of Acids and Bases ............................................................................................ 13 4 Comparing the Strength of Acids and Bases ........................................................................ 15 4.1 pH / Concentration of H+ ................................................................................................... 15 4.2 Acid Dissociation Constant, Ka ......................................................................................... 16 4.3 Base Dissociation Constant, Kb ........................................................................................ 17 4.4 Relationship between Ka, Kb and Kw (not in H1 syllabus) ................................................. 18 4.5 Degree of Dissociation,  (not in H1 syllabus) ................................................................. 19 5 Calculating the pH of Acids and Bases ................................................................................. 21 5.1 Strong Acids and Bases ................................................................................................... 21 5.2 Weak Acids and Bases (not in H1 syllabus) ..................................................................... 22 6 Acid and Base Properties of Salt Solutions .......................................................................... 26 6.1 Salt Hydrolysis .................................................................................................................. 26 6.2 Calculating pH of Salt Solutions ....................................................................................... 27 7 Buffer Solutions ....................................................................................................................... 30 7.1 Acidic Buffer ..................................................................................................................... 30 7.2 Basic Buffer ...................................................................................................................... 31 7.3 pH of a Buffer (not in H1 syllabus) .................................................................................... 32 7.4 Buffer Capacity ................................................................................................................. 33 7.5 Uses of Buffers ................................................................................................................. 35 8 Indicators .................................................................................................................................. 37 9 Titration Curves ....................................................................................................................... 39 9.1 Strong Acid – Strong Base Titration ................................................................................. 39 9.2 Weak Acid – Strong Base Titration ................................................................................... 42 9.3 Strong Acid – Weak Base Titration ................................................................................... 44 9.4 Weak Acid – Weak Base Titration (not required to know) ................................................ 46 9.5 Polyprotic (polybasic) Acid – Strong Base Titration .......................................................... 48 9.6 Double Indicator Titrations ................................................................................................ 50 10 APPENDIX ................................................................................................................................. 52 10.1 The Levelling Effect of Water ........................................................................................... 52 10.2 Effect of Concentration on Calculation of pH .................................................................... 54 11 Answers to Self Check Questions .......................................................................................... 56

A c i d - B a s e E q u i l i b r i a E u n o i a J u n i o r C o l l e g e 3 | P a g e 1 Theories of Acids and Bases LO (a) show understanding of and apply the Arrhenius theory of acids and bases (b) show understanding of and apply the Brønsted -Lowry theory of acids and bases, including the concept of conjugate acids and conjugate bases (c) show understanding of and apply the Lewis theory of acids and bases (including non - aqueous system, e.g. reaction between B