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Chemistry · Moles & Stoichiometry

Flip through 20 full sample pages with substantial teaching notes, deep-dive explanations, worked practice, exam application and self-check questions.

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Overview

Moles and stoichiometry

Stoichiometry translates a chemical equation into measurable quantities. This sample develops amount of substance, molar mass, particles, balanced equations, limiting reagents, concentrations, gas volumes and yield.

  • mole
  • molar mass
  • equations
  • limiting reagents
Worked example / practice: If 18.0 g of water has M = 18.0 g mol⁻¹, n = m/M = 1.00 mol.

Deep-dive notes

The central idea on this page is moles and stoichiometry. To use it confidently, connect the definition or rule above to the specific details listed here: mole; molar mass; equations. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Moles and stoichiometry” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain moles and stoichiometry without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Write the balanced equation before doing mole ratios.
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Mole

Amount of substance

The mole is the SI unit for amount of substance. It is a counting unit: one mole contains a fixed number of specified entities.

  • symbol n
  • unit mol
  • specify atoms/molecules/ions
  • connect microscopic particles to macroscopic mass
Worked example / practice: A sample containing 0.50 mol of molecules contains half Avogadro's constant in molecules.

Deep-dive notes

The central idea on this page is amount of substance. To use it confidently, connect the definition or rule above to the specific details listed here: symbol n; unit mol; specify atoms/molecules/ions. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Amount of substance” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain amount of substance without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Always state what particles are being counted.
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Avogadro

Particles and moles

Avogadro's constant links moles to particles: N = nN_A, where N_A ≈ 6.022×10²³ mol⁻¹.

  • N = number of entities
  • n = moles
  • N_A = Avogadro constant
  • rearrange n=N/N_A
Worked example / practice: 2.0 mol contains about 1.2044×10²⁴ specified particles.

Deep-dive notes

The central idea on this page is particles and moles. To use it confidently, connect the definition or rule above to the specific details listed here: N = number of entities; n = moles; N_A = Avogadro constant. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Particles and moles” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain particles and moles without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Keep scientific notation on your calculator until the final rounding.
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Molar mass

Mass and moles

Molar mass is the mass of one mole of substance, usually expressed in g mol⁻¹. For a compound, add the relative atomic masses according to the formula.

  • n=m/M
  • m=nM
  • M=m/n
  • use formula subscripts correctly
Worked example / practice: For CO₂, M≈12.01+2(16.00)=44.01 g mol⁻¹.

Deep-dive notes

The central idea on this page is mass and moles. To use it confidently, connect the definition or rule above to the specific details listed here: n=m/M; m=nM; M=m/n. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Mass and moles” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain mass and moles without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Do not confuse relative formula mass, which has no unit, with molar mass.
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Balanced equations

Conservation of atoms

Chemical equations must conserve each element. Coefficients give stoichiometric mole ratios and must not be replaced by changing chemical formula subscripts.

  • balance coefficients
  • count each element
  • simplest whole-number ratio
  • formulae remain chemically correct
Worked example / practice: 2H₂ + O₂ → 2H₂O means 2 mol H₂ react with 1 mol O₂.

Deep-dive notes

The central idea on this page is conservation of atoms. To use it confidently, connect the definition or rule above to the specific details listed here: balance coefficients; count each element; simplest whole-number ratio. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Conservation of atoms” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain conservation of atoms without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Mole ratios come from coefficients, not subscripts.
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Stoichiometry

Mole-ratio calculations

Convert the known quantity to moles, apply the equation coefficient ratio, then convert the required moles to the requested unit.

  • known → moles
  • ratio
  • required moles
  • convert to mass/volume/particles
Worked example / practice: For 2H₂+O₂→2H₂O, 3 mol O₂ can form 6 mol H₂O if H₂ is excess.

Deep-dive notes

The central idea on this page is mole-ratio calculations. To use it confidently, connect the definition or rule above to the specific details listed here: known → moles; ratio; required moles. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Mole-ratio calculations” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain mole-ratio calculations without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Write the ratio as a separate line to protect method marks.
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Limiting reagent

Which reactant runs out first?

The limiting reagent determines the maximum amount of product. Compare available moles relative to equation coefficients rather than comparing masses directly.

  • calculate moles of each
  • divide by coefficient
  • smallest scaled amount limits
  • excess remains
Worked example / practice: For N₂+3H₂→2NH₃, 1 mol N₂ needs 3 mol H₂. With only 2 mol H₂, H₂ is limiting.

Deep-dive notes

The central idea on this page is which reactant runs out first?. To use it confidently, connect the definition or rule above to the specific details listed here: calculate moles of each; divide by coefficient; smallest scaled amount limits. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Which reactant runs out first?” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain which reactant runs out first? without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Never identify the limiter from the smaller mass alone.
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Concentration

Solutions and molarity

Amount concentration is moles of solute per unit volume of solution. In mol dm⁻³ calculations, convert cm³ to dm³ by dividing by 1000.

  • c=n/V
  • n=cV
  • V in dm³
  • 1000 cm³ = 1 dm³
Worked example / practice: 0.20 mol in 500 cm³ = 0.20/0.500 = 0.40 mol dm⁻³.

Deep-dive notes

The central idea on this page is solutions and molarity. To use it confidently, connect the definition or rule above to the specific details listed here: c=n/V; n=cV; V in dm³. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Solutions and molarity” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain solutions and molarity without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Volume conversion is one of the most common stoichiometry errors.
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Dilution

Conserving solute amount

During dilution, solvent is added but the amount of dissolved solute stays constant, so c₁V₁=c₂V₂ when no solute is lost.

  • moles before = moles after
  • concentration decreases
  • total volume increases
  • use consistent volume units
Worked example / practice: 25.0 cm³ of 2.0 mol dm⁻³ diluted to 100 cm³ gives 0.50 mol dm⁻³.

Deep-dive notes

The central idea on this page is conserving solute amount. To use it confidently, connect the definition or rule above to the specific details listed here: moles before = moles after; concentration decreases; total volume increases. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Conserving solute amount” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain conserving solute amount without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Explain dilution in terms of same solute particles spread through more solution.
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Gases

Molar gas relationships

Gas calculations may use a molar gas volume under stated conditions or the ideal-gas equation pV=nRT. Always use the convention and units specified in the question.

  • state conditions
  • convert pressure/volume units if using pV=nRT
  • temperature in kelvin
  • use equation ratio first
Worked example / practice: At a stated molar gas volume of 24 dm³ mol⁻¹, 0.50 mol occupies 12 dm³.

Deep-dive notes

The central idea on this page is molar gas relationships. To use it confidently, connect the definition or rule above to the specific details listed here: state conditions; convert pressure/volume units if using pV=nRT; temperature in kelvin. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Molar gas relationships” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain molar gas relationships without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Do not use 24 dm³ mol⁻¹ blindly if different conditions or data are supplied.
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Empirical formula

Simplest whole-number ratio

An empirical formula gives the simplest whole-number atom ratio. Convert each element's mass or percentage to moles, divide by the smallest value and scale to whole numbers.

  • mass → moles
  • divide by smallest
  • identify near-simple fractions
  • scale
Worked example / practice: 40.0% C, 6.7% H, 53.3% O gives approximately CH₂O.

Deep-dive notes

The central idea on this page is simplest whole-number ratio. To use it confidently, connect the definition or rule above to the specific details listed here: mass → moles; divide by smallest; identify near-simple fractions. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Simplest whole-number ratio” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain simplest whole-number ratio without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Do not round 1.5 to 2; multiply the entire ratio by 2.
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Molecular formula

From empirical to molecular formula

The molecular formula is a whole-number multiple of the empirical formula. Compare molar mass with empirical-formula mass to find the multiplier.

  • find empirical formula mass
  • multiplier = molecular M / empirical mass
  • multiply all subscripts
Worked example / practice: Empirical CH₂O has mass 30; if molecular molar mass is 180, multiplier 6 → C₆H₁₂O₆.

Deep-dive notes

The central idea on this page is from empirical to molecular formula. To use it confidently, connect the definition or rule above to the specific details listed here: find empirical formula mass; multiplier = molecular M / empirical mass; multiply all subscripts. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “From empirical to molecular formula” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain from empirical to molecular formula without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: The multiplier should be very close to a whole number.
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Yield

Theoretical and percentage yield

Theoretical yield is the maximum predicted from stoichiometry. Actual yield may be lower because of incomplete reaction, losses, side reactions or equilibrium.

  • % yield = actual/theoretical ×100
  • same units
  • theoretical from limiting reagent
  • explain losses specifically
Worked example / practice: Theoretical 10.0 g, actual 8.2 g → 82% yield.

Deep-dive notes

The central idea on this page is theoretical and percentage yield. To use it confidently, connect the definition or rule above to the specific details listed here: % yield = actual/theoretical ×100; same units; theoretical from limiting reagent. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Theoretical and percentage yield” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain theoretical and percentage yield without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Avoid vague 'human error'; state a chemically plausible reason.
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Purity

Reacting sample versus pure substance

If a sample contains impurities, only the pure reactive fraction contributes to the stoichiometric calculation. Percentage purity compares mass of pure substance with total sample mass.

  • % purity = pure mass/sample mass ×100
  • identify active component
  • use stoichiometry to infer pure amount
Worked example / practice: A 5.0 g sample that contains 4.2 g active compound is 84% pure.

Deep-dive notes

The central idea on this page is reacting sample versus pure substance. To use it confidently, connect the definition or rule above to the specific details listed here: % purity = pure mass/sample mass ×100; identify active component; use stoichiometry to infer pure amount. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Reacting sample versus pure substance” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain reacting sample versus pure substance without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Keep purity and percentage yield conceptually separate.
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Titration

Stoichiometry in volumetric analysis

Titration uses a measured volume of one solution to determine amount or concentration of another. The balanced equation gives the reaction mole ratio.

  • pipette aliquot
  • burette titrant
  • endpoint
  • repeat concordant titres
  • calculate moles then ratio
Worked example / practice: If 25.0 cm³ acid reacts with 20.0 cm³ of known alkali, use the known alkali concentration to find its moles first.

Deep-dive notes

The central idea on this page is stoichiometry in volumetric analysis. To use it confidently, connect the definition or rule above to the specific details listed here: pipette aliquot; burette titrant; endpoint. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Stoichiometry in volumetric analysis” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain stoichiometry in volumetric analysis without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Use the mean of concordant titres, not the rough titre.
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Significant figures

Precision and chemical calculations

Quantitative chemistry should reflect measurement precision. Carry extra digits through intermediate steps and round only the final result to sensible significant figures.

  • units on every final quantity
  • avoid premature rounding
  • distinguish exact coefficients from measured data
  • check magnitude
Worked example / practice: If calculator gives 0.0049876 mol from 3 s.f. data, report 0.00499 mol.

Deep-dive notes

The central idea on this page is precision and chemical calculations. To use it confidently, connect the definition or rule above to the specific details listed here: units on every final quantity; avoid premature rounding; distinguish exact coefficients from measured data. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Precision and chemical calculations” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain precision and chemical calculations without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: A chemically correct method can still lose marks if units are missing.
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Exam method

A universal stoichiometry workflow

Many mole questions become routine if you follow a fixed pathway: equation → moles of known → ratio → moles required → requested quantity.

  • balance first
  • annotate units
  • show ratio
  • identify limiter if multiple reactants
Worked example / practice: Create a flow diagram on rough paper before a multi-stage problem.

Deep-dive notes

The central idea on this page is a universal stoichiometry workflow. To use it confidently, connect the definition or rule above to the specific details listed here: balance first; annotate units; show ratio. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “A universal stoichiometry workflow” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain a universal stoichiometry workflow without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Method marks reward visible chemistry, not an unexplained calculator result.
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Practice

Mixed mole questions

Try: 1) moles in 11.0 g CO₂. 2) particles in 0.25 mol. 3) concentration of 0.10 mol in 250 cm³. 4) mass of 0.50 mol NaCl.

  • use M(CO₂)≈44.0
  • N=nN_A
  • V=0.250 dm³
  • m=nM
Worked example / practice: Answers: ≈0.250 mol; ≈1.51×10²³ particles; 0.40 mol dm⁻³; ≈29.2 g NaCl.

Deep-dive notes

The central idea on this page is mixed mole questions. To use it confidently, connect the definition or rule above to the specific details listed here: use M(CO₂)≈44.0; N=nN_A; V=0.250 dm³. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Mixed mole questions” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain mixed mole questions without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: State formulas and units before checking the answer.
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Challenge

Limiting reagent practice

For 2Al+3Cl₂→2AlCl₃, suppose 0.40 mol Al reacts with 0.45 mol Cl₂. Compare available amounts against coefficients to identify the limiting reagent and product amount.

  • 0.40/2=0.20 reaction units
  • 0.45/3=0.15
  • Cl₂ limits
  • 0.30 mol AlCl₃ forms
Worked example / practice: The unused Al is 0.40−0.30 = 0.10 mol because product ratio Al:AlCl₃ is 1:1.

Deep-dive notes

The central idea on this page is limiting reagent practice. To use it confidently, connect the definition or rule above to the specific details listed here: 0.40/2=0.20 reaction units; 0.45/3=0.15; Cl₂ limits. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Limiting reagent practice” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain limiting reagent practice without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Scaled-mole comparison is faster and safer than guessing.
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Summary

Stoichiometry checklist

You should now be able to move between mass, moles, particles, solution concentration and equation ratios; determine limiting reagents; and evaluate yield and purity.

  • n=m/M
  • N=nN_A
  • c=n/V
  • balanced equation ratios
  • percentage calculations
Worked example / practice: Final challenge: design a problem combining concentration, limiting reagent and percentage yield.

Deep-dive notes

The central idea on this page is stoichiometry checklist. To use it confidently, connect the definition or rule above to the specific details listed here: n=m/M; N=nN_A; c=n/V. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Stoichiometry checklist” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain stoichiometry checklist without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: The full resource can extend into redox, energetics, equilibrium and exam-board-specific quantitative chemistry.
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