The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:
A mole is a scientific unit for measuring large quantities of small atoms and molecules. The mole is the amount of substance of a system that contains 6.02214076 ×10²³ specified elementary entities. For example, one mole of oxygen has a mass of 31.998 g and contains about 6.022 ×10²³ molecules of oxygen.
Carbon scale: Relative atomic mass(RAM) = Mass of 1 atom of an element/1/12th of the mass of one C-12 atom.Hydrogen scale: Mass of one atom of an element/Mass of one atom of Hydrogen
Gram Atomic Mass: It is the atomic mass of an element expressed in grams.
Relative Molecular Mass (Molecular weight)
Hydrogen scale: Mass of one molecule of a substance/mass of one atom of hydrogenCarbon scale: The relative molecular mass of an element represents how many times one molecule of the substance is heavier than 1/12th of the mass of the carbon-12 atom.
Gram Molecular Mass: Molecular mass of a substance expressed in grams. Gram Molecular Mass of all gases contains 6.022 ×10²³ number of molecules at S.T.P.
Gram Molecular Volume: Gram Molecular Mass/Mass per litre of gas at S.T.P. One mole of a gas occupies 22.4 lit at S.T.P.
A Mole of an element = Mass of the element/Atomic Mass or Gram atomic massMoles of a compound = Mass of the compound/Molecular Mass or Gram molecular massMass of one atom = Atomic Mass or Gram atomic mass/6.022 ×10²³ Mass of one molecule = Molecular Mass or Gram molecular mass/6.022 ×10²³ Number of atoms or molecules = Moles × 6.022 ×10²³
The law states that equal volumes of gases contain an equal number of molecules under identical temperature and pressure conditions.
V ∝ n, n is the number of moles. V =K n
For example, A molecule of N₂ contains two atoms of Nitrogen, and a molecule of NH₃ contains three atoms of hydrogen.
When one volume of hydrogen is reacted with one volume of chlorine at the same temperature and pressure, it gives two volumes of hydrogen chloride gas. The ratio of the reaction is 1:1:2
H₂ +Cl₂ → 2HCl
Relative Vapour Density = Mass of molecules of a gas or vapour/Mass of molecules of hydrogen measured at standard temperature and pressure.
According to Avogadro’s law, the volumes at standard temperature and pressure conditions may be substituted by molecules. So,
Relative vapour density = Mass of 1 molecule of gas or vapour/Mass of 2 atoms of Hydrogen
Relative molecular mass = Mass of 1 molecule of a substance/ Mass of 1 atom of Hydrogen
Vapour Density = Relative Molecular Mass/2
So, it becomes
Relative Molecular mass = 2 × Vapour Density
1. Mass of the solute /Mass of the solute+solvent × 1002. Total weight of an element in one molecule/Gram Molecular weight of the compound × 100
It is the ratio of atoms of different elements present in one molecule of a compound. The empirical formula of Glucose is CH₂O.
Determination of Empirical Formula
Percentage masses of Zn = 47.8 and Cl = 52.2
Atomic masses of Zn= 65 and Cl =35.5
Number of atoms of Zinc = 47.8/65 =0.73 and chlorine = 52.2/35 = 1.46
Simplest ratio of Zinc is 0.73/0.73 =1 and chlorine = 1.46/0.73 =2
The empirical formula of the compound is ZnCl₂.
The chemical formula denotes the actual number of atoms of different elements present in the compound’s one molecule.
Molecular formula = (Empirical formula)ₙ
Example: Molecular Formula of the Blue Vitriol is CuSO₄.5H₂O
Stoichiometry is relatively essential for understanding the relationship between reactants and products of chemical reactions. The reactions are balanced in terms of moles. A balanced chemical reaction gives equivalences in moles that allow stoichiometry calculations to be performed. The mole concept is a convenient method of expressing the amount of a substance.