Moles
Science, Chemistry. Usually met in years 10 and 11.
Use moles, mass and relative formula mass, and work out the mass of a product from a reacting mass.
What you practise
- Moles = mass ÷ Mr
- Mass from moles
- Reacting masses
Finishes with calculations from a balanced equation. Practice moves up a level when a round goes well and down when it does not.
Sample questions
Each sample comes with the method and the reason every wrong option is wrong. Real practice rounds are ten questions at your level.
Sample question, level 2 of 5
What is the mass of 1 mol of a substance with a relative formula mass of 44?
- 44 g
- 0.023 g
- 46 g
- 45 g
- 440 g
Show the answer and method
Answer: A, 44 g
The method: Mass = moles × Mr = 1 × 44 = 44 g.
Why the other options are wrong:
- B, 0.023 g: The division is upside down. Mass = moles × Mr.
- C, 46 g: Close, but check your working: this is a small slip away from the answer.
- D, 45 g: The moles and Mr were added.
- E, 440 g: The decimal point is one place out.
Sample question, level 4 of 5
How many moles are there in 88 g of CO₂? (Ar: C = 12, O = 16)
- 44
- 2
- 3
- 0.5
- 3872
Show the answer and method
Answer: B, 2
The method: Mr of CO₂ = 44. Moles = mass ÷ Mr = 88 ÷ 44 = 2 mol.
Why the other options are wrong:
- A, 44: Mr was subtracted from the mass.
- C, 3: Close, but check the division.
- D, 0.5: The division is upside down. Moles = mass ÷ Mr.
- E, 3872: The mass was multiplied by Mr. Moles = mass ÷ Mr.
See where this fits: GCSE science with AQA and Key Stage 3.
Related topics: States of matter, Atoms, Formula mass.
