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Year 10
AQA
Higher

Moles and masses

I can calculate mass of a substance or the number of moles it contains from data.

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New
New
Year 10
AQA
Higher

Moles and masses

I can calculate mass of a substance or the number of moles it contains from data.

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Share activities with pupils
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Lesson details

Key learning points

  1. The number of particles (atoms, ions, molecules etc.) in one mole of a substance is always the same.
  2. The mass of one mole of a substance is equal to the relative mass of the substance measured in grams.
  3. Mathematical relationships are manipulated to process practical results, calculating the number of moles in a substance.

Keywords

  • Mole - 1 mole of a substance is 6.02 × 10²³ particles of it. The mass of a mole of a substance is its relative mass in grams.

  • Avogadro's constant - Avogadro's constant is the number of particles in one mole of a substance (6.02 × 10²³ mol⁻¹).

  • Relative formula mass - The relative formula mass (RFM or Mᵣ) of a substance is the sum of the relative atomic masses of all the atoms in its formula.

Common misconception

Pupils struggle to link a mole to number of particles.

Use real world examples of converting volumes / masses into number of particles so pupils become more comfortable converting between moles, number of particles particles and masses.

Alter the final task into a competition - who can fit the highest number of water molecules onto a penny? Challenge pupils to peer evaluate each other's working out to ensure the winners have correctly calculated the number of molecules. Consider extending to include different coins.
Teacher tip

Equipment

balances, pennies, small beakers, water, dropping pipettes, paper towels, calculators

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which of the following is the correct chemical formula for calcium carbonate?
CACO3
CaCo₃
CaCO
Correct answer: CaCO₃
CaC
Q2.
Match each keyword to the correct definition.
Correct Answer:chemical equation,describes a reaction, indicating the reactants and products

describes a reaction, indicating the reactants and products

Correct Answer:chemical formula,shows the number of atoms of each element in a substance

shows the number of atoms of each element in a substance

Correct Answer:coefficient,number placed in front of a chemical formula to balance an equation

number placed in front of a chemical formula to balance an equation

Correct Answer:subscript,written slightly below and to the side of another character

written slightly below and to the side of another character

Correct Answer:state symbol,indicates the physical state of substances in a reaction

indicates the physical state of substances in a reaction

Q3.
Which chemical equation is correctly balanced?
Mg + Cl → MgCl
Mg + Cl₂ → MgCl
Correct answer: Mg + Cl₂ → MgCl₂
Mg + 2Cl → MgCl₂
Q4.
Match each element to its correct relative atomic mass.
Correct Answer:He,4

4

Correct Answer:Be,9

9

Correct Answer:F,19

19

Correct Answer:Ne,20

20

Correct Answer:B,11

11

Correct Answer:Na,23

23

Q5.
The relative formula mass of sodium sulfide, Na₂S is .
Correct Answer: 78, 23 + 23 + 32, (23 × 2) + 32
Q6.
The relative formula mass of Al(OH)₃ is .
Correct Answer: 78, 27 + 16 + 16 + 16 + 1 + 1 + 1, 27 + (17 × 3), 27 + 3(16 + 1), 27 + 3×(16 + 1)

Exit quiz

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6 Questions

Q1.
Which equation best matches this description of a chemical reaction? "Four moles of aluminium atoms react with three moles of oxygen molecules to form two moles of aluminium oxide formula units".
2Al₂O₃ → 4Al + 3O₂
4Al → 2Al₂O₃ + 3O₂
3O₂ → 2Al₂O₃ + 4Al
Correct answer: 4Al + 3O₂ → 2Al₂O₃
Q2.
Which of the following shows a correct mathematical relationship between moles, mass (g), and a substance's relative formula mass (RFM)?
moles = mass (g) × relative formula mass
mass (g) = moles ÷ relative formula mass
Correct answer: mass (g) = moles × relative formula mass
Correct answer: moles = mass (g) ÷ relative formula mass
Q3.
The standard unit for mass in chemistry is .
Correct Answer: grams, gram
Q4.
Sort the following substances into order of increasing mass.
1 - 1 mole of hydrogen
2 - 1 mole of sodium
3 - 1 mole of HCl
4 - 1 mole of sodium chloride
5 - 1 mole of Na₂O
6 - 1 mole of Cl₂
Q5.
How does the number of particles in 10 g of nitric acid, HNO₃, compare to the number of particles in 10 g of nitrogen?
Correct answer: There are fewer nitric acid particles in 10 g
There are the same number of particles of nitrogen and nitric acid in 10 g
There are more nitric acid particles in 10 g
Q6.
Match the mass (g) of the following substances to the correct number of moles.
Correct Answer:6 g carbon ,0.5 mol

0.5 mol

Correct Answer:31 g phosphorus,1.0 mol

1.0 mol

Correct Answer:70 g MgS,1.25 mol

1.25 mol

Correct Answer:39 g LiF,1.5 mol

1.5 mol

Correct Answer:280 g Br₂,1.75 mol

1.75 mol

Correct Answer:80 g oxygen,2.5 mol

2.5 mol