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Module 5: Physical chemistry and transition elements (5.1.3 Acids, bases and buffers)

7 dot points across 7 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do we calculate the pH of acids, bases and buffers, and why do buffers resist change?

The Bronsted-Lowry model and conjugate pairs, pH and the ionic product of water Kw, the acid dissociation constant Ka and pKa for weak acids, buffer action and pH, titration curves, and indicator choice.
An OCR H432 module 5 answer on acids and bases: Bronsted-Lowry conjugate pairs, pH and Kw, Ka and pKa for weak acids, buffer action and pH calculations, titration curves, and choosing an indicator.
13 min answer →

Why do some endothermic reactions still happen, and how do we predict feasibility?

Entropy as a measure of disorder, calculating entropy change of reaction, and the Gibbs free energy equation to decide feasibility and find the temperature at which a reaction becomes feasible.
An OCR H432 module 5 answer on entropy and free energy: entropy as disorder, calculating entropy change of reaction, and using the Gibbs free energy equation to decide feasibility and find the temperature of feasibility.
12 min answer →

How do we quantify the position of equilibrium, and what changes its value?

The equilibrium constant Kc in terms of concentrations and Kp in terms of partial pressures and mole fractions, calculations from equilibrium amounts, and the effect of temperature and catalysts on the constant.
An OCR H432 module 5 answer on equilibrium constants: writing and calculating Kc from concentrations and Kp from partial pressures and mole fractions, and the effect of temperature and catalysts on the value of the constant.
12 min answer →

How do we find the lattice enthalpy of an ionic solid, and what makes it large?

Lattice enthalpy and its determination by Born-Haber cycles, the enthalpy changes involved (formation, atomisation, ionisation, electron affinity), enthalpies of solution and hydration, and the effect of ionic charge and radius.
An OCR H432 module 5 answer on lattice enthalpy: the Born-Haber cycle and its enthalpy terms, calculating lattice enthalpy by Hess's law, enthalpies of solution and hydration, and the effect of ionic charge and radius on their magnitudes.
13 min answer →

How do we find the rate equation of a reaction, and what does it tell us about the mechanism?

Orders of reaction and the rate equation, the rate constant and its units, concentration-time and rate-concentration graphs, half-life, the rate-determining step, and the Arrhenius equation.
An OCR H432 module 5 answer on rates: orders and the rate equation, the rate constant and its units, concentration-time and rate-concentration graphs, the rate-determining step, and the Arrhenius equation.
12 min answer →

How do standard electrode potentials let us predict which redox reactions happen?

Redox half-equations, standard electrode potentials measured against the standard hydrogen electrode, cell notation and standard cell potential, predicting feasibility, and storage and fuel cells.
An OCR H432 module 5 answer on electrochemistry: redox half-equations, standard electrode potentials and the standard hydrogen electrode, cell notation and standard cell potential, predicting feasibility, and fuel cells.
13 min answer →

What gives the transition metals their colours, complexes and catalytic power?

Definition and electron configurations of transition elements (including the chromium and copper exceptions), complex ions, ligands and shapes, ligand substitution with colour changes, precipitation reactions, the origin of colour, and catalysis.
An OCR H432 module 5 answer on transition elements: the definition and electron configurations (with the chromium and copper exceptions), complex ions and shapes, ligand substitution with colour changes, precipitation reactions, the origin of colour, and catalysis.
13 min answer →