2022_H1_Theories of acids and bases_notes (teacher)

1 St. Andrew’s Junior College H1 Chemistry 2022 Lecture Notes Theories of Acids and Bases Assessment Objectives Candidates should be able to: (a) show understanding of, and apply the Arrhenius theory of acids and bases (b) show understanding of, and apply the Bronsted-Lowry theory of acids and bases, including the concept of conjugate acids and bases; (c) explain qualitatively the differences in behaviour between strong and weak acids and bases in terms of the extent of dissociation; (d) explain the terms pH; Ka; Kb; Kw [The relationship Kw = KaKb is not required]; (e) calculate [H+(aq)] and pH values for strong acids, and strong bases; (f) explain the choice of suitable indicators for acid-base titrations, given appropriate data, in terms of the strengths of the acids and bases; (g) (i) explain how buffer solutions control pH; (ii) describe and explain the uses of buffers, including the role of H2CO3/HCO3- in controlling pH in blood. Lecture Outline: 1. Theories of acids and bases 2. Autoionisation of water 3. Dissociation of weak acid and bases 4. Acid-Base Properties of Salt Solutions 5. Indicators for acid-base titrations 6. Monoprotic Acid-Base Titration Curves 7. Buffer solutions References: 1. Chemistry by Silberberg 2. Chemistry by Raymond Chang 3. Chemistry for Advanced level by Peter Cann 4. Chemistry in context by Hill and Holman 5. A – level Chemistry by Ramsden

2 1. THEORIES OF ACIDS AND BASES 1.1 Arrhenius theory of acids and bases An Arrhenius acid is a substance that produces H+ in aqueous solution. An Arrhenius base is a substance that produces OH– in aqueous solution. E.g.: HNO3(l) + H2O(l) NO3–(aq) + H3O+(aq) Note: H3O+ is hydronium ion, which is the same as H+ (aq) NaOH(s) + aq Na+(aq) + OH–(aq)  An acid-base reaction involves the formation of salt and water 1.2 Brønsted–Lowry theory of acids and bases A Brønsted–Lowry acid is a proton (H+) donor. A Brønsted–Lowry base is a proton (H+) acceptor. base conjugate acid E.g.: NH3(aq) + H2O(l) NH4+(aq) + OH–(aq) Acid conjugate base base conjugate acid E.g.: HCl(g) + NH3 (g) NH4Cl(s) acid conjugate base  An acid–base reaction involves the transfer of a proton from the acid to the base.  When a Br ønsted–Lowry acid (HA) loses a proton, the resulting product (A –) is called the conjugate base of HA.  When a Brønsted–Lowry base (B) accepts a proton, the resulting product (BH+) is called Candidates should be able to:  show understanding of, and apply the Arrhenius theory of acids and bases  show understanding of, and apply the Brønsted–Lowry theory of acids and bases, including the concept of conjugate acids and conjugate bases

3 the conjugate acid of B.  A conjugate acid