SOME BASIC CONCEPTS IN CHEMISTRY — Ultra-condensed NEET Cheat Sheet

Must-Know Constants

• Nₐ = $6.022 \times 10^{23}$ $mol^{-1}$
• 1 amu = $1.66054 \times 10^{-24}$ g
• Molar volume at STP = 22.4 L/mol (0 °C, 1 atm)

Core Formulas

Empirical Formula Steps

1. Divide % by atomic mass
2. Divide all by the smallest ratio
3. Round to whole numbers (multiply by 2, 3 if needed)
4. n = Mr / EF mass → Molecular formula = n × EF

Concentration Temperature Dependence

• T-dependent: Molarity, Normality (involve volume)
• T-independent: Molality, Mole fraction, Mass%, ppm (involve mass)

Limiting Reagent Rule

Divide moles of each reactant by its stoichiometric coefficient. Smallest = limiting reagent.

Laws — Chronological (Lavoisier → Avogadro)

1789 Conservation → 1799 Definite → 1803 Multiple → 1808 Gay-Lussac → 1811 Avogadro

Classic NEET Traps

• 4 g $H_{2}$ + 32 g $O_{2}$ → 2$H_{2}$ + $O_{2}$: Both consumed (no excess)
• 0.98 atomic ratio → round to 1; 1.48 → do NOT round, multiply EF by 2
• 22.4 L/mol valid only at STP, not 25 °C
• Normality ≠ Molarity unless n-factor = 1