Core Practicals and Synoptic Questions
Notes on practical skills, all sixteen core practicals on one card each, eight new practical and synoptic questions with full worked solutions, and recall cards for your review days. Nothing here is copied from the book.
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Read one section at a time, then answer its check question before you open the answer.
12.1 How practical work is examined
Practical work is assessed in two separate ways.
- Written papers: questions on the core practicals and practical skills appear on all three papers. Paper 3 (General and Practical Principles in Chemistry) carries the most: data analysis, uncertainties, planning and evaluating methods.
- The practical endorsement: your teacher assesses your hands-on competence through the year against the Common Practical Assessment Criteria (CPAC). It is reported separately as Pass or Not classified and does not change your grade, but many universities expect a pass.
Exam questions often describe a core practical with something changed: a different reagent, different apparatus, or unfamiliar data. Learn the principles behind each practical, not just the steps.
Check yourself: Does the practical endorsement affect your A-level grade?
No; it is reported separately as Pass or Not classified
12.2 The core practicals, one card each
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12.4 Uncertainty, error, accuracy and precision
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12.5 Results tables and graphs
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12.6 Planning an experiment, and risk
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12.7 Synoptic questions
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Extra worked questions
Cover the solution, answer on paper, then mark yourself against each step. Each step shows the mark it earns.
All 8 worked solutions are free for members. The first one is open to everyone.
Uncertainty in a pipette
A 25.0 cm3 pipette has an uncertainty of ±0.06 cm3. Calculate the percentage uncertainty, and explain why it is not doubled as a burette's is.
Try it first, then show the worked solution
| Percentage | 0.06 ÷ 25.0 × 100 = 0.24% | 1 |
|---|---|---|
| Not doubled | A pipette delivers a fixed volume from one measurement, while a burette titre comes from two readings | 1 |
Answer: 0.24%
Examiner tip: Double only when the value comes from two readings.
Variables in a rate experiment
In a rate practical, a student times how long a cross takes to disappear at five temperatures. Identify the independent variable, the dependent variable and two control variables.
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Accurate or precise?
The true enthalpy of neutralisation is −57 kJ mol−1. Student A gets −49, −50, −49. Student B gets −52, −60, −58. Comment on the accuracy and precision of each set and suggest the main error in A's results.
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Total uncertainty in a titration
A concentration is calculated from a titre of 23.50 cm3 (burette ±0.05 cm3 per reading), a 25.0 cm3 pipette (±0.06 cm3) and a 250 cm3 volumetric flask (±0.3 cm3). Calculate the total percentage uncertainty.
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Reading a gradient
A student plots ln k against 1/T. The line of best fit passes through (3.10 × 10−3, −2.30) and (3.40 × 10−3, −4.10). Calculate the gradient and use it to find Ea. R = 8.31 J K−1 mol−1.
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Planning: identify a carbonate
A student has about 2 g of a Group 1 carbonate, M2CO3, and 0.100 mol dm−3 HCl. Outline a titration method to find the Mr of the carbonate.
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Purity of limestone
2.00 g of limestone is heated to constant mass. The mass falls by 0.86 g. Assume only the CaCO3 decomposes: CaCO3 → CaO + CO2. (a) Calculate the percentage of CaCO3. (b) Why heat to constant mass? (c) Suggest why the decomposition needs a high temperature, using ΔG = ΔH − TΔS.
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Concentration and Ka from one experiment
25.0 cm3 of a weak acid HA needs 20.00 cm3 of 0.125 mol dm−3 NaOH for neutralisation. When 10.00 cm3 of the NaOH has been added, the pH is 4.20. (a) Calculate [HA]. (b) Find Ka. (c) Predict the pH of the original acid.
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Recall cards
Answer out loud or on paper before you turn the card. Only a complete answer counts as "Got it".
These are 3 of 18 recall cards. Premium members get the full deck for every topic, ready for each review day in their plan.
Your review days
Count from your Day 0, the day you finish learning this week. Your plan schedules these for you.
- +1 Recall cards (these online cards, or the cards in the book)
- +3 Recall cards and Q1 to Q4
- +7 Recall cards and Q5 to Q8
- +14 Recall cards and Q9 to Q12
- +30 Full section test, timed
All questions on this page are original and are not in the book. This site is independent and is not endorsed by AQA or Pearson Edexcel.