Common Misconceptions
Part of Moles & Calculations — GCSE Chemistry
This common misconceptions covers Common Misconceptions within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 22 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 10 of 15 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 15
Practice
22 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).