Some Basic Concepts Of Chemistry Part - 7 | Class 11th

Que. Find the molecular mass of  HNO₃, C₁₂H₂₂O₁₁ And C₆H₁₂O₆ 

Ans. 

Mass of Hydrogen = 1

Mass of Nitrogen = 14

Mass of Oxygen = 16

Mass of Carbon = 12

Mass of HNO₃ = 1 + 14 + 3 × 16 = 1 + 14 + 48 = 63u

Mass of C₁₂H₂₂O₁₁ = 12 × 12 + 22 × 1 + 11 × 16 = 144 + 22 + 176 = 342u

Mass of C₆H₁₂O₆ = 12 × 6 + 1 × 12 +  16 × 6 = 72 + 12 + 96 = 180u

Mole (n): It is amount of a substance that contains as many particles or entities as the number of atoms in exactly 12 grams of pure C-12.

1 mole of any substance contains 6.022 x 10²³ atoms. This number is known as Avogadro number or Avogadro constant (N_A or N₀).

1 mole of a substance = Molar mass of substance = Avogadro’s Number of chemical units = 22.4L volume at STP of gaseous substance.

e.g., 1 mole of CH₄ = 16g of CH₄ = 6.022 × 10²³ molecules of CH₄ = 22.4L at STP.

         n =   Given Mass     =   Volume(at STP) =  x Particles    =  MV

                Molecular Mass         22.4L                       N_A             1000

1 mol of hydrogen atoms = 6.022×10²³ atoms

1 mol of water molecules = 6.022×10²³ water molecules

1 mol of sodium chloride = 6.022 × 10²³ formula units of sodium chloride

Molar volume (MV): It is the volume of 1 mole of any substance. At standard temperature and pressure (STP), molar volume of any gas = 22.4 L (or, 22400 mL). i.e. 22.4 L of any gas at STP contains 1 mole of the gas or 6.022 x 10²³ molecules of the gas and its mass = molar mass. For e.g.

22.4 L of hydrogen gas = 1 mole of H₂ = 6.022x10²³ molecules of hydrogen = 2 g of H₂

1 Mole of atoms = Gram atomic mass or molar mass = 6.022 x 10²³ molecules = 22.4 L at NTP (0⁰C, 1atm) = 22.7 L at STP (0⁰C, 1 bar).