Quantitative ChemistryCommon Misconceptions

Common Misconceptions

Part of Moles & Calculations · GCSE GCSE Chemistry revision

This common misconceptions covers Common Misconceptions within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 27 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 10 of 17 in this topic. Use this common misconceptions to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 10 of 17

Practice

27 questions

Recall

20 flashcards

⚠️ Common Misconceptions

Misconception 1: "A mole is a unit of mass"

A mole is a unit of amount of substance (a count of particles), not mass. The mass of one mole depends on which substance you have — one mole of carbon is 12 g, but one mole of water is 18 g. Always use Mr to convert between moles and grams.

Misconception 2: "Mr has units (like grams)"

Relative formula mass (Mr) is a dimensionless ratio — it compares the mass of a compound to 1/12 the mass of a carbon-12 atom. It has no units. When you write "Mr of CO₂ = 44," you do not write "44 g." It is only when you say "the molar mass is 44 g/mol" that units appear.

Misconception 3: "If some mass appears to disappear in a reaction, the law of conservation of mass is broken"

Mass is always conserved. If mass seems to decrease, a gas has escaped the container (e.g., CO₂ leaving an open beaker). If mass appears to increase, a gas from the air has been incorporated (e.g., oxygen joining magnesium during combustion).

Keep building this topic

Read this section alongside the surrounding pages in Moles & Calculations. That gives you the full topic sequence instead of a single isolated revision point.

Worked Example — Full Method Memory Aids The Story of Counting the Uncountable Moles Formula Triangle

Practice Questions for Moles & Calculations

One mole of any substance contains how many particles?

A. 6.02 × 10²³
B. 6.02 × 10²⁰
C. 3.01 × 10²³
D. 6.02 × 10¹⁸

1 markfoundation

Explain why the percentage yield of a reaction is never 100% in practice.

2 marksstandard

Quick Recall Flashcards

What is Avogadro's constant?

6.02 × 10²³ particles per mole This is the number of particles in one mole of any substance.

Define 'one mole'

The amount of substance containing 6.02 × 10²³ particles One mole of any element weighs exactly its Ar in grams

27 questions on Moles & Calculations — practise free

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Worked Example — Full Method

Memory Aids