Cambridge International AS Level Chemistry Practical Skills (Paper 3)

Measuring the 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.

Enthalpy Change via Hess’s Law

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

Concentration of Hydrochloric Acid by Titration

Practical Skills: Titration: 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.

Preparation of a Standard Solution

Practical Skills: Standard Solutions: 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 Halogenoalkanes

Practical Skills: Rates of Hydrolysis: comparing the rates of hydrolysis of halogenoalkanes 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.

Preparing an Organic Liquid: Chlorination of 2-methylpropan-2-ol

The chlorination of 2-methylpropan-2-ol (Practical Skills: Organic Preparation): 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.

Oxidation of an Alcohol: Distillation and Reflux

Practical Skills: Distillation and Reflux: oxidation of ethanol to ethanal by distillation and to ethanoic acid by reflux, with apparatus, boiling points, equations, product tests and exam points.

Qualitative Analysis of Inorganic and Organic Unknowns

Practical Skills: Qualitative Analysis: 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.

Rates of Reaction: Timing an Observation

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.

Gravimetric Analysis: Water of Crystallisation and Composition of a Solid

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

Redox Titrations: Manganate(VII) and Iodine–Thiosulfate

Redox titrations: potassium manganate(VII) with iron(II), hydrogen peroxide and ethanedioate, iodine–thiosulfate with starch, mole ratios from half-equations and errors.

Following Reaction Rates: 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.

The Effect of Temperature on the Rate of a Reaction

The effect of temperature on rate: a clock reaction at five temperatures, 1/t as the relative rate, the Boltzmann explanation, errors and improvements.

Measuring pH: the Ka of a Weak Acid

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.

Electrochemical Cells: Measuring Cell Potentials

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.

Preparing a Transition Metal Complex

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

Qualitative Analysis at A Level: Transition Metal Ions and Organic Unknowns

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

Preparing and Purifying 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.