OCR A Level Chemistry Practical Activity Groups (PAGs)

PAG 1 Moles Determination: Molar Volume of a Gas

Measuring the molar volume of a gas: collecting CO₂ over water, the graph of volume against mass, the calculation to 24 dm³ mol⁻¹, percentage uncertainty and the errors examiners ask about.

PAG 3 Enthalpy Determination: Hess’s Law

PAG 3: enthalpy change via Hess’s law from K₂CO₃ and KHCO₃ with HCl, with q = mcΔT, the Hess cycle, percentage uncertainty and error analysis.

PAG 2 Acid–Base Titration

PAG 2: finding the concentration of hydrochloric acid by titration with standardised sodium hydroxide, with method reasons, concordant titres, the worked calculation, error directions and percentage uncertainty.

PAG 2 Preparing a Standard Solution

PAG 2: preparing a standard solution of sulfamic acid and using it to find the concentration of sodium hydroxide by titration, with method, sample data, calculation, uncertainty and common errors.

Comparing the Rates of Hydrolysis of Haloalkanes

Practical Skills: Rates of Hydrolysis: comparing the rates of hydrolysis of haloalkanes with aqueous silver nitrate in ethanol at 50 °C, the role of each reagent, silver halide colours, 1/t, bond enthalpies and carbocation stability, with errors, improvements and exam points.

PAG 5 Synthesis of an Organic Liquid: 2-chloro-2-methylpropane

The chlorination of 2-methylpropan-2-ol (PAG 5): Sₙ1 mechanism via the tertiary carbocation, separating funnel technique, hydrogencarbonate wash, drying, simple distillation at 50–52 °C, silver nitrate test with nitric acid, worked percentage yield and evaluation.

PAG 5 Oxidation of an Alcohol: Distil or Reflux

PAG 5: oxidation of ethanol to ethanal by distillation and to ethanoic acid by reflux, with apparatus, boiling points, equations, product tests and exam points.

PAG 4 and PAG 7 Qualitative Analysis of Unknowns

PAG 4 and PAG 7: identifying unknown organic liquids and inorganic solids by test-tube reactions, with the method, safety, ionic equations with state symbols, the evidence trail, exam data practice and interactive checks.

Measuring Rates of Reaction: Mass, Gas Volume and Time

Measuring rates of reaction: sodium thiosulfate and acid, rate ∝ 1/t, the effect of temperature and concentration, gas syringe and mass loss methods, tangents and errors.

PAG 1 Moles Determination: Water of Crystallisation and Composition by Mass

Gravimetric analysis: water of crystallisation by heating to constant mass, crucible technique, thermal decomposition of carbonates, composition calculations and errors.

PAG 9 and PAG 10 Rates of Reaction: Continuous Monitoring and Initial Rates

Following reaction rates: the iodination of propanone by titration (zero order in iodine), the iodine clock reaction, initial rates from 1/t, rate equations, mechanism, errors and uncertainty.

Finding the Activation Energy of a Reaction: the Arrhenius Plot

Finding the activation energy of a reaction: a clock reaction at five temperatures, the Arrhenius plot of ln(1/t) against 1/T, gradient = (−Eₐ) / (R), the worked calculation, errors and improvements.

PAG 11 pH Measurement: the Ka of a Weak Acid and Buffers

Finding the Ka of a weak acid: pH meter calibration, Ka from pH, half-neutralisation and pH = pKa, the weak acid pH curve, indicators, buffer action and errors.

PAG 8 Electrochemical Cells

Measuring cell potentials: half-cells, salt bridge, high-resistance voltmeter, E⦵cell = +1.10 V for zinc–copper, concentration effects, the standard hydrogen electrode, feasibility, errors and uncertainty.

Redox Titrations: Manganate(VII) and Iodine–Thiosulfate

Redox titrations: iron(II) with potassium manganate(VII), iodine with sodium thiosulfate, mole ratios from half-equations, worked calculations, uncertainty and errors.

Preparing a Transition Element Complex

Preparing a transition element complex: tetraamminediaquacopper(II) sulfate from copper(II) sulfate and ammonia, ligand substitution, colours, ethanol crystallisation, filtration, washing, drying and percentage yield.

Qualitative Analysis of Transition Element Ions and Organic Unknowns

Identifying transition element ions with sodium hydroxide and ammonia, the second-year organic functional group tests, and worked inorganic and organic unknowns with their equations.

PAG 6 Synthesis of an Organic Solid: Aspirin

The preparation of aspirin: 2-hydroxybenzoic acid with ethanoic anhydride, recrystallisation, filtration under reduced pressure, percentage yield, the melting point, TLC and the iron(III) chloride test as tests of purity, and the common errors.

Thin-Layer Chromatography: Separating and Identifying Compounds

Thin-layer chromatography: the method with reasons, adsorption against solubility, calculating and comparing Rf values with standards, visualising spots, checking purity and evaluating errors.

PAG 12 Research Skills: Researching, Referencing and Reporting

Research skills for CPAC 5: online and offline sources, judging reliability, Harvard citations and reference lists, planning a back titration from research, uncertainty and reporting.