Cambridge IGCSE Chemistry · Syllabus 0620 · Stoichiometry
Amount of substance
What is Amount of substance?
Amount of substance is the quantity measured in moles that counts how many specified particles are present; it is calculated from mass divided by molar mass, and it is the quantity a balanced chemical equation compares between substances.
This definition is part of the Stoichiometry chapter in Cambridge IGCSE Chemistry.
Common mistakes with Amount of substance
- 11. Applying a 1:1 shortcut to a titration that is not 1:1 Repair The relationship written as \(c_1V_1 = c_2V_2\) hides the equation ratio, and is only correct when that ratio happens to be \(1:1\). Go through amount of substance instead — it costs one extra line and works every time. Lesson 3.3G Supplement 3.3.6
- "A mole is a very large mass." Fix A mole is an amount of substance, not a mass. One mole of hydrogen molecules has a mass of about \(2\ \mathrm{g}\); one mole of lead atoms has a mass of about \(207\ \mathrm{g}\). Same amount, very different masses.
- "\(n = M/m\)." Fix Inverted. Substitute the units and see: \(\mathrm{g\,mol^{-1}} \div \mathrm{g} = \mathrm{mol^{-1}}\), which is not an amount of substance. The correct arrangement, \(m/M\), gives \(\mathrm{mol}\).