Some Basic Concepts of ChemistryNEET Chemistry · Class 11 · NCERT Chapter 1

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• 9 g of H₂O is 0.5 mol and 3.011 × 10²³ molecules. This exact number appears in NEET almost every year.
• Switch to "Particles" and type 6.022e23 — you always get exactly 1 mol regardless of compound.
• Pick CO₂ (M = 44), enter 22 g — you get 0.5 mol and 11.2 L at STP. That 11.2 L is half the molar volume.

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• Glucose and acetic acid share the same empirical formula CH₂O — the molar mass is what distinguishes them.
• When the divided ratios are near 1.5 or 2.5, the multiplier will be 2. If near 1.33 or 1.67, multiply by 3.
• NEET 2023 asked: a compound with 40% C, 6.67% H, 53.33% O and molar mass 60 → CH₂O × 2 = C₂H₄O₂ (acetic acid).

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• In Haber process with 28 g N₂ and 3 g H₂: N₂ ratio = 1/1 = 1.0, H₂ ratio = 1.5/3 = 0.5 → H₂ is limiting.
• Always divide moles by stoichiometric coefficient — the reactant with the smallest ratio runs out first.
• In water formation with excess O₂: slide O₂ up to 200 g — still limited by H₂. See the excess O₂ value.

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• 5.85 g NaCl in 500 mL → 0.1 mol ÷ 0.5 L = 0.2 M. Confirm with this calculator.
• Dilution: 2 M HCl × 100 mL = 0.5 M × V₂ → V₂ = 400 mL. Always add water to acid, not acid to water.
• Remember: molarity = moles per litre of solution (not per litre of solvent).