Some Basic Concepts in Chemistry: Mistakes to Avoid

Using 22.4 L/mol outside STP: 22.4 L/mol applies only at 0 °C and 1 atm. At 25 °C and 1 atm, molar volume is ~24.5 L/mol. Always check stated conditions.
Moles ≠ mass: 1 mole of $H_{2}$ = 2 g; 1 mole of NaCl = 58.5 g. The mole is a count, not a fixed mass.
Limiting reagent by mass, not moles: The reactant with smaller mass is NOT necessarily the limiting reagent. Compare moles ÷ stoichiometric coefficient, not raw masses.
Both reactants consumed when ratio is stoichiometric: When moles are in exact stoichiometric proportion (e.g., 4 g $H_{2}$ + 32 g $O_{2}$ ), neither is "limiting" — both are completely consumed. A common NEET trap.
Rounding atomic ratios: Ratios of 0.98 or 1.02 can be rounded to 1, but 1.48 or 1.52 cannot — they require multiplying the entire empirical formula by 2.
Confusing mass% with mole fraction: Both are dimensionless, but mass% uses mass ratios while mole fraction uses mole ratios.
Molarity used for colligative property calculations: $\Delta Tb$ = Kb × m uses molality, not molarity. Using M introduces temperature-dependent error.
n-factor assumed to be always 2 for $H_{2}$$SO_{4}$ : n-factor = 2 only in neutralisation (donates 2 $H^{+}$ ). In other reactions the n-factor may differ.
Avogadro's number written as $6.023 \times 10^{23}$ : The correct value is $6.022 \times 10^{23}$ $mol^{-1}$ .