Chemistry • Year 11 • Module 2 • Lesson 5
Mole Calculations — Consolidation
Lock in every formula, unit, and pathway from Lessons 1–4 before tackling multi-step problems. Focus: formula recall, key terms, and identifying which formula applies.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: mole, Avogadro’s number, molar mass, empirical formula, molecular formula, molar volume, STP, SATP, calculation pathway, multi-step problem, intermediate value, unit analysis. 12 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | The SI unit of amount of substance; the amount containing exactly 6.022 × 1023 elementary entities. | |
| 1.2 | The number 6.022 × 1023 mol−1; the number of entities per mole of substance. | |
| 1.3 | The mass (in grams) of one mole of a substance; obtained by summing atomic masses from the periodic table. | |
| 1.4 | The simplest whole-number ratio of atoms in a compound (e.g. CH2O for glucose). | |
| 1.5 | The actual number of each type of atom in one molecule of a compound (e.g. C6H12O6 for glucose). | |
| 1.6 | The volume occupied by one mole of gas at specified temperature and pressure; units: L mol−1. | |
| 1.7 | Standard temperature and pressure: 0 °C and 100 kPa; molar volume = 22.71 L mol−1. | |
| 1.8 | Standard ambient temperature and pressure: 25 °C and 100 kPa; molar volume = 24.8 L mol−1. | |
| 1.9 | A sequence of formula rearrangements used to convert a given quantity into a required quantity via moles. | |
| 1.10 | A problem requiring two or more conversions; moles always serve as the central “currency”. | |
| 1.11 | A calculated result (e.g. moles) that is not the final answer but is required for the next step. | |
| 1.12 | Tracking how units cancel at each step to confirm the correct formula and rearrangement were used. |
2. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 9 marks (1 per blank)
Word bank:
Avogadro · currency · empirical · four · intermediate · molar mass · moles · SATP · whole number
There are ___________ main mole-calculation pathways in Inquiry Question 1. In every multi-step problem, ___________ serve as the central ___________ — every other quantity must be converted through moles first. To find the number of particles (N) from moles, multiply by ___________’s number (NA = 6.022 × 1023 mol−1). To find moles from mass, divide the mass by the ___________. To convert a gas volume at ___________ (25 °C, 100 kPa) to moles, divide the volume by 24.8 L mol−1. When deriving a molecular formula, the ___________ formula is found first using the 4-step method; the multiplier n must always be a ___________. Any calculated moles value that is needed for the next step but is not the final answer is called an ___________ value.
3. True or false — with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 12 marks (1 T/F + 1 correction each)
3.1 At SATP (25 °C, 100 kPa), one mole of any gas occupies 22.71 L. T / F
3.2 The empirical formula of a compound gives the simplest whole-number ratio of atoms, not necessarily the actual number of atoms per molecule. T / F
3.3 When converting mass to a number of particles, it is valid to skip the moles step and multiply mass directly by Avogadro’s number. T / F
3.4 In the formula n = m ÷ MM, the unit of molar mass (MM) is g mol−1. T / F
3.5 When calculating the molar mass of Al2(SO4)3, the subscript 3 outside the brackets means there are 3 sulfur atoms and 4 oxygen atoms. T / F
3.6 Intermediate values in a multi-step calculation should be rounded to 3 significant figures before use in the next step. T / F
4. Formula and unit recall
Answer each question in 1–2 sentences or with the formula and units. 8 marks (2 each)
4.1 State the formula that converts between moles and number of particles, defining each symbol and giving its unit.
4.2 Write the formula used to find the number of moles of a gas from its volume, and state the two values of molar volume used in NSW HSC Chemistry with their conditions.
4.3 A student knows the empirical formula and the molar mass of a compound. Write the formula that gives the multiplier n needed to find the molecular formula.
4.4 State the three rearrangements of n = m ÷ MM and the quantity each rearrangement is used to find.
5. Build the mole hub map
The five terms below are the key quantities in Inquiry Question 1. Draw labelled arrows between them to show how they are connected. Each arrow must carry a formula or operation (e.g. “÷ NA”, “× MM”). Aim for at least 6 labelled arrows. 6 marks (1 per valid labelled arrow)
Terms: n (moles) · N (particles) · m (mass) · V (gas volume) · EF/MF (formula).
Q1 — Term–definition match
1.1 mole • 1.2 Avogadro’s number • 1.3 molar mass • 1.4 empirical formula • 1.5 molecular formula • 1.6 molar volume • 1.7 STP • 1.8 SATP • 1.9 calculation pathway • 1.10 multi-step problem • 1.11 intermediate value • 1.12 unit analysis.
Marking criteria: 1 mark per correct term. Accept minor spelling variations. No half marks.
Q2 — Cloze paragraph
In order: four / moles / currency / Avogadro / molar mass / SATP / empirical / whole number / intermediate.
Marking criteria: 1 mark per correctly placed word. Accept equivalent phrasing only where the word bank term was unavoidable. Words must match the blank’s grammatical context.
Q3 — True / false with correction
3.1 False. At SATP (25 °C, 100 kPa) the molar volume is 24.8 L mol−1. 22.71 L mol−1 is the value at STP (0 °C, 100 kPa).
3.2 True.
3.3 False. All pathways pass through moles. To convert mass to number of particles: first find n = m ÷ MM, then N = n × NA. You cannot skip the moles step.
3.4 True.
3.5 False. The subscript 3 outside the brackets applies to both S and O inside. Al2(SO4)3 contains 2 Al, 3 S, and 12 O atoms (3 × 4 = 12 O).
3.6 False. Intermediate values should be carried at full calculator precision throughout all steps; only the final answer is rounded to the appropriate number of significant figures. Premature rounding accumulates error in multi-step problems.
Marking criteria: 1 mark for correct T/F; 1 mark for a correct, precise correction on each false statement. No mark for correction if T/F is wrong.
Q4.1 — Particles formula
N = n × NA, where N = number of particles (no unit), n = amount in moles (mol), NA = Avogadro’s number = 6.022 × 1023 mol−1. Rearranges to n = N ÷ NA.
Marking: 1 mark for correct formula; 1 mark for correct units of each variable.
Q4.2 — Gas volume formula
n = V ÷ Vm, where n = moles (mol), V = gas volume (L), Vm = molar volume (L mol−1). At STP (0 °C, 100 kPa): Vm = 22.71 L mol−1. At SATP (25 °C, 100 kPa): Vm = 24.8 L mol−1.
Marking: 1 mark for formula with units; 1 mark for both Vm values with correct conditions.
Q4.3 — Molecular formula multiplier
n (multiplier) = MM(compound) ÷ MM(EF). Then: MF = EF × n.
Marking: 1 mark for the multiplier formula; 1 mark for stating MF = EF × n.
Q4.4 — Three rearrangements of n = m ÷ MM
(1) n = m ÷ MM — used to find moles from mass. (2) m = n × MM — used to find mass from moles. (3) MM = m ÷ n — used to find molar mass from a measured mass and known moles.
Marking: 1 mark per correct rearrangement with its purpose stated. Deduct 1 mark if units are omitted from all three.
Q5 — Mole hub concept map
Award 1 mark per valid labelled arrow (minimum 6). Correct arrows include:
- n → × NA → N
- N → ÷ NA → n
- n → × MM → m
- m → ÷ MM → n
- n → × Vm → V
- V → ÷ Vm → n
- n → ÷ MM(EF) gives multiplier → EF/MF
- EF → × n → MF
Arrows in both directions count separately. Reject arrows that lack any operation label.