Mole Concept

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The SI base unit for amount of substance is 'mole' (symbol: mol). It represents the amount of a substance that contains as many elementary entities (atoms, molecules, ions) as there are atoms in exact

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The mole concept is needed because atoms and molecules are extremely small and present in huge numbers. It's impractical to count them individually. Just like we use 'dozen' for 12 items, we use 'mole

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Avogadro's constant (Nₐ) is the number of elementary entities present in one mole of any substance. Its value is 6.022 × 10²³ mol⁻¹. This constant helps us connect the microscopic world of atoms and m

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1 km = 1.0 × 10³ m = 1000 m 1 mg = 1.0 × 10⁻³ g = 0.001 g 1 μm = 1.0 × 10⁻⁶ m = 0.000001 m Remember: kilo (k) = 10³, milli (m) = 10⁻³, micro (μ) = 10⁻⁶

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Atomic mass unit (amu) is a unit of mass used to express atomic and molecular masses. It is defined as exactly 1/12th of the mass of one carbon-12 atom. 1 amu = mass of one C-12 atom ÷ 12. It's also c

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Molecular mass of H₂O = (2 × atomic mass of H) + (1 × atomic mass of O) = (2 × 1) + (1 × 16) = 2 + 16 = 18 amu Therefore, molecular mass of water = 18 amu

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Molar mass is the mass of one mole of a substance, expressed in g mol⁻¹. It is numerically equal to the relative atomic mass (for elements) or relative molecular mass (for compounds), but has units of

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Number of molecules = number of moles × Avogadro's constant Number of Cl₂ molecules = 0.25 mol × 6.022 × 10²³ mol⁻¹ = 1.506 × 10²³ molecules Note: Each Cl₂ molecule contains 2 Cl atoms, so total Cl at