Formulae, Equations and Amounts of Substance | Edexcel A-Level Chemistry (9CH0)
Formulae, Equations and Amounts of Substance
- 134 questions
- 8 subtopics
- Topics 2, 3 and 5, examined on all three papers
- Paper 1, Paper 2 and Paper 3
Covers the mole and the three routes to it, the ideal gas equation, balancing and reacting quantities, titration and standard solutions, yield and atom economy, and the practical and mathematical skills the papers assume..
It covers the mole, molar mass and empirical formula, the ideal gas equation and molar volume, equations, concentration and reacting quantities, standard solutions, titration and uncertainty, percentage yield, atom economy and acid reactions, core practicals 1 to 3, empirical formula and water of crystallisation by experiment and apparatus, uncertainty and mathematical skills.
Sample questions from Formulae, Equations and Amounts of Substance
Answer each one closed book first, then open the answer.
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The mole, molar mass and empirical formula
State the formula used to calculate the amount of substance in moles from mass.
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n = m/M, where n is the amount in moles, m is the mass in grams, and M is the molar mass in g mol⁻¹. -
The ideal gas equation and molar volume
Calculate the amount of substance when pressure = 158000 Pa, volume = 0.0016 m³, gas constant = 8.31 J K⁻¹ mol⁻¹, temperature = 344 K.
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Amount of substance = (158000 × 0.0016) ÷ (8.31 × 344) = 0.0884 mol. -
Equations, concentration and reacting quantities
Convert a volume of 724 cm³ into dm³.
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Volume = 724 ÷ 1000 = 0.724 dm³. -
Standard solutions, titration and uncertainty
State the formula for calculating percentage uncertainty.
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Percentage uncertainty = (absolute uncertainty / measured value) × 100% -
Percentage yield, atom economy and acid reactions
What products are formed when an acid reacts with a metal?
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A salt and hydrogen gas. -
Core practicals 1 to 3
In Core Practical 2, what is the first step in preparing the standard solution?
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Accurately weigh the solid acid. -
Empirical formula and water of crystallisation by experiment
After achieving constant mass, how is the empirical formula determined?
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Calculate masses of each element, convert to moles, and determine the simplest whole number ratio. -
Apparatus, uncertainty and mathematical skills
What must be retained when converting between standard and ordinary form?
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Significant figures.
The 8 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| The mole, molar mass and empirical formula | Recall questions on the Avogadro constant, molar mass, and working out empirical and molecular formulae from masses or percentages. | 15 |
| The ideal gas equation and molar volume | The ideal gas equation pV = nRT and the value of R, rearranging it to find an amount of gas, finding the molar mass of a volatile liquid from its mass and the volume, temperature and pressure of its vapour, and what makes a chemical equation balanced. | 9 |
| Equations, concentration and reacting quantities | State symbols, ionic equations and spectator ions, n = c × V and converting cm³ to dm³, the amount of gas from molar volume, reacting masses and reacting gas volumes from a balanced equation, converting mol dm⁻³ to g dm⁻³, and the equivalence point and indicator colours in a titration. | 20 |
| Standard solutions, titration and uncertainty | The steps for making up a standard solution, calculating percentage uncertainty and percentage error, random and systematic errors, accuracy against precision and concordant titres, and comparing a result's percentage error with its total percentage uncertainty. | 19 |
| Percentage yield, atom economy and acid reactions | Percentage yield and theoretical yield, atom economy and why a high value is desirable, displacement reactions, the products of acids with metals, carbonates, metal oxides and alkalis, precipitation reactions, and hazard, risk and laboratory precautions. | 21 |
| Core practicals 1 to 3 | The steps of Core Practical 1 measuring the molar volume of a gas, Core Practical 2 making a standard solution of a solid acid to find the concentration of sodium hydroxide, and Core Practical 3 titrating to find the concentration of hydrochloric acid. | 15 |
| Empirical formula and water of crystallisation by experiment | Finding an empirical formula by heating a substance in a crucible to constant mass, defining water of crystallisation, and finding x in a hydrated salt by heating, cooling and reweighing to constant mass and comparing the moles of anhydrous salt and water. | 12 |
| Apparatus, uncertainty and mathematical skills | The measurements, heating methods and apparatus used in practical work, hazardous substances, unit conversions, standard form and significant figures, selecting concordant titres and burette uncertainty, rearranging equations, independent, dependent and control variables, and the symbols ∝, ≪, ≫, ~ and ⇌. | 23 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
Edexcel A-Level Chemistry Active Recall Guide
Every topic, not just this one. 1,534 questions with their answers.