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Concept of Mole
Mole
A mole is defined as the amount of substance which contains the Avogadro Number of particles.
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.
Molar Mass
- Molar mass is the mass of 1 mol of substance.
- The unit of molar mass is g/mol.
- The molar mass of a substance is always equal to its relative atomic mass or relative molecular mass in the unit of g/mol.
Example:
Relative atomic mass of oxygen atom = 16, hence the molar mass of oxygen atom = 16g/mol
Relative moleculoar mass of oxygen molecule (O2) = 32, hence the molar mass of oxygen molecule is 32g/mol
(Avogadro constant = 6.02 x 1023)
Answer
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.
Answer:
Number of mole = 1.806 x 1021 ÷ 6.02 x 1023 = 0.003 mol
(Relative atomic mass: N = 14; H = 1)
Answer:
Relative molecular mass of ammonia (NH3)
= 14 + 3(1) = 17.
Therefore, the molar mass of ammonia = 17g/mol
Mass of 2.5 mol ammonia = 2.5 x 17 = 42.5g
(Relative Atomic Mass: Sodium = 23)
Answer:
Molar mass of sodium = 23g/mol
Number of moles of sodium = 69 ÷ 23 = 3 mol.
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).
Asnwer:
1 mol gas ≡ 24 dm3 = 24000cm3
Number of moles of nitrogen = 1200 ÷ 24000 = 0.05 mol
(Molar volmue of gas at s.t.p. = 22.4dm3/mol)
Answer:
Volume of nitrogen gas = 2 x 22.4 = 44.8 dm3
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