The three acid–base theories, Ostwald's dilution law, pH of strong and weak acids and of mixtures, the common-ion effect, Ksp and precipitation, buffers by Henderson–Hasselbalch, and salt hydrolysis by salt type.
Unit 1, Physical chemistry, carries 17 of the 50 chemistry marks — joint-heaviest in the subject. With fourteen chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). Along with volumetric analysis it is the most numerical chapter of the unit, and its pH arithmetic reappears in Analytic chemistry.
The MEC scope line runs: Arrhenius theory of ionisation. Arrhenius, Brønsted–Lowry and Lewis acids and bases. Ostwald's dilution law. Ionic product of water; pKa, pKb, pH and pOH. Common-ion effect, solubility and solubility product, and their applications. Acidic and basic buffer solutions. Types of salts and qualitative hydrolysis of salts. Related numerical problems. The headings below are its points, in MEC's order.
Three ways it comes: recall (the conjugate base of HSO₄⁻, the Lewis definition, Kw at 25 °C); understanding (why adding NH₄Cl suppresses the ionisation of NH₄OH, why an aqueous solution of NH₄Cl is acidic); application (the pH of a weak acid, of a mixture, of a buffer; whether a precipitate forms).
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