AS and A2 Chemistry notes and resources (WJEC specification) - UNIT CH5 Physical and inorganic chemistry

This unit develops ideas of redox, kinetics, energy changes and equilibria. The inorganic chemistry of some elements in various sections of the Periodic Table is studied.

20.2 - Acid-Base Equilibria

Candidates should be able to:

(h) understand and apply the Lowry-Bronsted theory of acids and bases (limited to aqueous solutions).

(i) recall the definition of pH and calculate pH values from those of [H+ (aq)] and vice versa.

(j) understand and appreciate the distinction between the terms concentrated/dilute and strong/weak and explain the differences in behaviour between strong and weak acids and bases, using Ka.

(k) appreciate the significance of the ionic product of water, Kw, and understand that neutralisation involves H+(aq) + OH- (aq) --> H2O(l)

(l) explain and use pH, Kw and Ka in calculations involving strong and weak acids, and use pH and Kw in calculations involving strong bases.

(m) recall the forms of the acid - base titration curves for the systems: strong acid /strong base (e.g. HCl/NaOH), strong acid/ weak base (e.g. HCl/NH3) and weak acid/strong base (e.g. CH3COOH/NaOH), explaining these in terms of the appropriate acid and base strengths.

(n) understand the mode of action of buffer solutions, exemplified by the CH3COONa / CH3COOH and NH3/NH4+ systems, appreciate their importance, and carry out appropriate calculations using pH, Kw and Ka.

(o) recall, and explain qualitatively, typical pH values exhibited by solutions of salts of strong acid / strong base (e.g. NaCl) strong acid / weak base (e.g. NH4Cl) and weak acid / strong base (e.g. CH3COONa).

(p) understand the working of an indicator and select suitable indicators for specified acid-base titrations, given appropriate pH values.