# Some Basic Concepts of Chemistry Notes | SwaVid Some Basic Concepts of Chemistry, NCERT Class 11 Chemistry: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-11/chemistry/chapter/some-basic-concepts-of-chemistry Source: https://www.swavid.com/cbse/class-11/chemistry/chapter/some-basic-concepts-of-chemistry # Some Basic Concepts of Chemistry ## Formulas and definitions ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 11 Chemistry on SwaVid ### Matter and its classification ### Measurement and significant figures ### Laws of chemical combination ### Atomic and molecular masses ### Mole concept and molar mass ### Percentage composition and empirical formulas ### Stoichiometry and limiting reagent ### Reactions in solutions ### Next chapter ### Related chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 11 › Chemistry › Some Basic Concepts of Chemistry Notes written by SwaVid from the NCERT textbook. Class 11 Chemistry, Unit 1. Key ideas, formulas and common mistakes. CBSE prints 7 marks for Unit 1, not for this chapter alone. Short answer. This chapter introduces the fundamental quantitative tools of chemistry, including measurement units, significant figures, and the laws of chemical combination. It explains how the mole concept links atomic masses, molecular formulas, and stoichiometric calculations in chemical reactions. Source: NCERT Chemistry Part I (Reprint 2026-27) , Unit 1, Some Basic Concepts of Chemistry Matter exists as solids, liquids, or gases and can be classified into pure substances and mixtures. Pure substances comprise elements and compounds, whereas mixtures can be homogeneous or heterogeneous. Properties of matter are measured using SI units. The uncertainty in experimental measurements is handled using scientific notation and significant figures, which follow definite rounding rules. Chemical reactions obey the laws of conservation of mass, definite proportions, multiple proportions, and Gay-Lussac's law of gaseous volumes. Avogadro's law explains these observations by stating that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Atomic mass is measured relative to the carbon-12 isotope, where 1 unified mass unit (1 u) equals 1/12th the mass of a ¹²C atom. Molecular mass is the sum of atomic masses of the elements in a molecule, while formula mass is used for ionic compounds. One mole contains exactly 6.022 × 10²³ elementary entities, known as the Avogadro constant. The mass of one mole of a substance in grams is numerically equal to its atomic or molecular mass in unified mass units. The mass percent of each element gives the empirical formula, which represents the simplest whole-number ratio of atoms in a compound. The molecular formula shows the exact number of atoms and is a whole-number multiple of the empirical formula. A balanced chemical equation provides the quantitative mole relationships between reactants and products. The limiting reagent is the reactant that is completely consumed first, limiting the amount of product formed. The concentration of a solution is expressed as mass percent, mole fraction, molarity, or molality. Molarity depends on temperature because solution volume changes with temperature, whereas molality and mole fraction do not. Try each question first. Then tap it to see the answer. Molar mass of C₂H₅OH = 2(12.01) + 6(1.008) + 16.00 = 46.068 g mol⁻¹ Mass of carbon in 1 mole = 2 × 12.01 = 24.02 g Mass percent = (24.02 / 46.068) × 100 = 52.14% 52.14% Moles of NaOH = 4.0 g / 40.0 g mol⁻¹ = 0.10 mol Volume in litres = 250 mL / 1000 = 0.250 L Molarity = 0.10 mol / 0.250 L = 0.40 mol L⁻¹ 0.40 M Moles of N₂ = 28.0 g / 28.0 g mol⁻¹ = 1.00 mol Moles of H₂ = 12.0 g / 2.016 g mol⁻¹ ≈ 5.95 mol Mole-to-coefficient ratio: N₂ = 1.00 / 1 = 1.00; H₂ = 5.95 / 3 = 1.98. N₂ is the limiting reagent. Moles of NH₃ formed = 2 × moles of N₂ = 2 × 1.00 mol = 2.00 mol N₂ is the limiting reagent; 2.00 mol NH₃ Structure of Atom . Thermodynamics . Redox Reactions . The 9 chapters of Class 11 Chemistry . CBSE does not give marks to one chapter. It prints 7 marks for Unit 1, Some Basic Concepts of Chemistry, which includes Some Basic Concepts of Chemistry. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Structure of Atom. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Unit 1 NCERT book - 7 marks, Unit 1 - 3 quick checks - Confusing molarity and molality in temperature variation problems . Remember that molarity uses volume of solution, which expands or contracts with temperature. Molality uses mass of solvent, which is completely independent of temperature. - Identifying the limiting reagent solely by comparing given masses or given moles . Divide the given moles of each reactant by its stoichiometric coefficient in the balanced equation. The reactant with the lowest ratio is the limiting reagent. - Using total solution mass instead of solvent mass in the molality denominator . Subtract the mass of solute from the total mass of the solution to obtain the mass of solvent before calculating molality. - Reporting significant figures incorrectly in addition and multiplication . For addition and subtraction, round to the fewest decimal places. 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