Playbook
Some Basic Concepts of Chemistry
51 q - 1.33/paper - 2% HARD, and rising. Mole arithmetic that every Calculate chapter reuses.
- Questions in the bank
- 51
- q/paper (2024–25 papers)
- 1.33
- Tagged HARD
- 2%
- Subtopics
- 4
Strand: Calculate
When you’ll see it
Moles from a mass, a volume at STP or a number of particles; a limiting reagent; a percentage composition or a molarity.
How this chapter is tested
51 q at 1.33 a paper, 2% HARD — and rising, from 1.15 a paper in 2023-24 to 1.54 in 2025. The mole page is 31 questions: mass ↔ moles ↔ particles ↔ volume, with 22.4 dm³ per mole of gas at STP.
The same arithmetic runs through every Calculate chapter, so these hours pay twice. The one HARD question type is H₂O₂ volume strength converted to percent by mass.
The sub-skills
The distinct skills inside the chapter, in the order to learn them.
Mole conversions
n = m/M = N/N_A = V/22.4 dm³ (gas at STP).
Stoichiometry
Convert to moles, scale by the balanced equation, convert back. Find the limiting reagent first.
Concentration
Molarity = moles per litre of solution; molality = moles per kg of solvent.
Traps to expect
Distractor shapes this chapter reuses. The Traps page covers the patterns that cut across chapters.
Mass ratio as mole ratio
An equation's coefficients are MOLE ratios. 2H₂ + O₂ → 2H₂O means 4 g of hydrogen with 32 g of oxygen, not 2:1 by mass.
Molecules against atoms
One mole of O₂ has N_A molecules and 2N_A atoms. The question's wording decides which.
Learn it before you drill it
This chapter has full teaching notes — foundations, worked examples, self-checks and a per-subtopic mastery checkpoint. Read the notes once, then drill subtopic by subtopic below.
Some Basic Concepts of Chemistry notesDrill every some basic concepts of chemistry question
51 questions from the bank, scoped to 4 bundled subtopics.
Drill one subtopic at a time
The 4 subtopics this playbook covers, in catalog order.
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