OCR A A Level Chemistry Practical Activity Groups
Use this landing page to move between the OCR A A Level Chemistry practical activity group (PAG) revision pages for the first year of the course. Each page gives the method with the reason for every step, the apparatus, the data processing, the uncertainty and the evaluation points that the written papers reward, together with the practical techniques examined in Modules 2 to 4.
Choose a Practical Page
Practical questions test more than a memorised method. Students need to understand apparatus choices, measurement quality, data processing, uncertainty, risk management and how each practical links to the underlying chemistry.
Key idea: The strongest practical answers connect observations and data to chemical reasoning, while using precise apparatus vocabulary and clear evaluation of errors or limitations.
Practical activity groups for the first year
Techniques and procedures from Modules 2, 3 and 4, assessed in every written paper.
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.
Start revisingPAG 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.
Start revisingPAG 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.
Start revisingPAG 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.
Start revisingComparing 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.
Start revisingPAG 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.
Start revisingPAG 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.
Start revisingPAG 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.
Start revisingMeasuring 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.
Start revisingPAG 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.
Start revisingHow to Use These Practical Pages
Start with the practical that matches the topic you are studying, then return to this page before revising practical skills. For each practical, make sure you can state the purpose, describe the method accurately, process the data and explain how errors, uncertainty and safety affect the quality of the result.
Exam focus: Practise explaining method improvements, identifying sources of error, choosing suitable apparatus and linking observations to valid conclusions.
Copyright notice: This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.
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