Concept of Mole
Card 1: Define mole?
A mole is defined as the amount of substance which contains the Avogadro Number of particles.
Card 2: State the meaning of Avogadro Constant.
The Avogadro Number (or Avogadro Constant) is defined as the number of atoms in 12 g of the carbon-12 isotope, which is equal to 6.02 x 1023.
Card 3: What is the meaning of molar mass.
Relative moleculoar mass of oxygen molecule (O2) = 32, hence the molar mass of oxygen molecule is 32g/mol
Card 4: Interconversion of number of moles and number of particles.
Number of Moles ↔ Number of Particles
Find the number of molecules in 2.5 mol of ammonia.
(Avogadro constant = 6.02 x 1023)
Number of molecules = 2.5 x (6.02 x 1023) = 1.505 x 1024 molecules.
Calculate the mole of ammonia that contain 1.806 x 1021 ammonia molecule.
Number of mole = 1.806 x 1021 ÷ 6.02 x 1023 = 0.003 mol
Card 5: Interconversion of number of moles and mass of substance.
Number of Moles ↔ Mass of Substance
Find the mass of 2.5 mol ammonia (NH3).
(Relative atomic mass: N = 14; H = 1)
Relative molecular mass of ammonia (NH3)
= 14 + 3(1) = 17.
Mass of 2.5 mol ammonia = 2.5 x 17 = 42.5g
How many moles of atom exist in 69g of sodium metal?
(Relative Atomic Mass: Sodium = 23)
Molar mass of sodium = 23g/mol
Number of moles of sodium = 69 ÷ 23 = 3 mol.
Card 6: State the meaning of molar volume of gas.
Molar Volume of Gas
Molar volume of gas is the volume of 1 mole gas.
One mol of any gas occupies a volume of 24 dm3 (24 000 cm3 ) at room temperature(25oC) and pressure or 22.4 dm3 (22400cm3) at s.t.p. (Standard Temperature(0oC) and Pressure).
Card 7: Interconversion of number of moles and volume of gas.
Number of Moles ↔ Volume of Gas
Find the number of moles of nitrogen molecule in 1200cm3 of nitrogen gas at room temperature. (Molar volmue of gas at room temperature = 24dm3/mol)
1 mol gas ≡ 24 dm3 = 24000cm3
Number of moles of nitrogen = 1200 ÷ 24000 = 0.05 mol
Find the volume of 2 mol nitrogen gas at s.t.p.
(Molar volmue of gas at s.t.p. = 22.4dm3/mol)
Volume of nitrogen gas = 2 x 22.4 = 44.8 dm3