Some Basic Concepts in Chemistry: 5 Must-Know Facts

1 mol = $6.022 \times 10^{23}$ entities = molar mass in grams = 22.4 L at STP (0 °C, 1 atm).
Molecular formula = n × empirical formula, where n = molar mass ÷ EF mass; EF from % composition by dividing each % by atomic mass then simplifying.
Limiting reagent = reactant with smallest (moles ÷ stoichiometric coefficient); when both reactants are in exact stoichiometric proportion, neither is limiting.
Molarity is temperature-dependent (uses volume); molality is temperature-independent (uses mass of solvent); interconvert via M = (1000 × d × w%) / (Mr × 100).
Normality = Molarity × n-factor; n-factor = 2 for $H_{2}SO_{4}$ in neutralisation, = 1 for HCl/NaOH; equivalent weight = molar mass ÷ n-factor.