MINDMAPS FOR UPSCPET 2026 · VISUAL REVISION
One mole: distinguish atoms from molecules
Check the chemical entity before converting moles to grams
Mole, particles and molar mass
A mole counts specified entities
- One mole contains exactly 6.02214076 × 10²³ specified elementary entities.
- The entity must be stated: atoms, molecules, ions, electrons or formula units.
- At school precision, molar mass in g mol⁻¹ has the same numerical value as particle mass in u.
O, O₂ and O₃
- Using O ≈ 16 u, one mole of O atoms has mass ≈ 16 g.
- One mole of O₂ molecules has mass ≈ 2 × 16 = 32 g.
- One mole of O₃ molecules has mass ≈ 3 × 16 = 48 g.
Mass → moles → particles
- Number of moles n = given mass (m) ÷ molar mass (M).
- Number of specified entities N = nNₐ, where Nₐ = 6.02214076 × 10²³ mol⁻¹.
- Example: 16 g of O₂ gas is 0.5 mol of O₂ molecules, but contains 1.0 mol of O atoms.
Check the entity first
- Never use 32 g for '1 mole of oxygen atoms' or 16 g for '1 mole of oxygen gas (O₂)'.
- For X₂, molecular molar mass is twice the atomic molar mass of X.
- Equal moles of different substances have equal particle counts, not equal masses.
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