Measurement of Matter

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The Law of Conservation of Matter states that 'there is no rise or drop in the mass of matter during a chemical reaction.' It was proposed by French scientist Antoine Lavoisier in 1785. The total mass…

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The Law of Constant Proportion states that 'the proportion by mass of constituent elements in different samples of a compound is fixed.' Proposed by J.L. Proust in 1794. Example: In water (H₂O), hydro…

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Atomic radius is the distance between the nucleus of an atom and its outermost orbit. It determines the size of an atom. Unit: nanometre (nm), where 1 nm = 10⁻⁹ m. Atoms are extremely tiny, with hydro…

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Atomic mass number is the total number of protons and neutrons in an atomic nucleus. Today, atomic mass is expressed in Unified Mass Unit (u), also called Dalton. 1u = 1.66053904 × 10⁻²⁷ kg. Carbon-12…

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Molecular mass is the sum of atomic masses of all atoms in a molecule. For H₂O: H = 1u (2 atoms), O = 16u (1 atom). Molecular mass = (1 × 2) + (16 × 1) = 2 + 16 = 18u. Unit is Dalton (u).

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A mole is the quantity of a substance whose mass in grams equals its molecular mass in Daltons. 1 mole = molecular mass in grams. Formula: Number of moles (n) = Mass of substance (g) / Molecular mass.

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Avogadro's number (Nₐ) is the number of molecules in one mole of any substance. Value: 6.022 × 10²³. This means 1 mole of any substance contains 6.022 × 10²³ molecules. Named after Italian scientist A…

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Step 1: Molecular mass of CO₂ = 12 + (16×2) = 44u. Step 2: Number of moles = 66/44 = 1.5 mol. Step 3: Number of molecules = 1.5 × 6.022 × 10²³ = 9.033 × 10²³ molecules.