This article provides you the revision notes on Class 11 Chemistry: Chapter- Some Basic Concepts of Chemistry, to give you a quick glance of the chapter. This article is a continuation of the revision notes on Class 11 Chemistry, Chapter- Some Basic Concepts of Chemistry, Part-I. In Part-I you got to learn about matter and its classification, basic physical quantities and their measurement.
Topics covered in this part of chapter notes for ‘Some Basic Concepts of Chemistry’, are:
The key notes of the chapter are as follows:
Laws of Chemical Combinations
There are 5 basic laws governing combination of elements to form compounds.
1. Law of Conservation of Mass (Antoine Lavoisier in 1789)
This law states that matter (mass) can neither be created nor destroyed.
2. Law of Definite Proportions (Louis Proust in 1799)
This law states that a chemical compound always consists of the same elements combined together in the same ratio, irrespective of the method of preparation or the source from where it is taken.
3. Law of Multiple Proportions (Dalton in 1803)
This law states that when two elements combine to form two or more compounds, then the different masses of one element, which combine with a fixed mass of the other, bear a simple ratio to one another.
4. Gay Lussac’s Law of Gaseous Volumes (Lussac in 1808)
This law states that under similar conditions of temperature and pressure, whenever gases react together, the volumes of the reacting gases as well as products bear a simple whole number ratio.
H2 (g) + O2(g) → H2O (g)
100 mL 50 mL 100 mL
Here, the volumes of hydrogen and oxygen which combine together (i.e. 100 mL and 50 mL) bear a simple ratio of 2:1.
5. Avogadro Law (Avogadro in 1811)
According to this law equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
Dalton's Atomic Theory:
Basic postulates of Dalton's Atomic Theory are:
It is the smallest particle of an element, which may or may not have independent existence is called an atom. For example, oxygen (O), hydrogen (H), etc.
It is the smallest particle of a substance which is capable of independent existence. For example, H2O, O2, etc.
Atomic and Molecular Masses
Gram Atomic Mass:
Atomic mass of an element expressed in grams is the gram atomic mass or gram atom
Formula Unit Mass:
Empirical Formula for Molecular Formula
Relationship between empirical and molecular formulae:
The representation of a chemical change in terms of symbols and formulae of the substances involved in the reaction is called chemical equation.
It is the reactant which gets consumed first or limits the amount of product formed.
For a balanced reaction reaction:
A +B → C + D
B would be a limiting reagent if nA /nB > nB/nA
Similarly, A is a limiting reagent if nA /nB < nB/nA
Concentration of the solutions
Parts per million ( ppm):
Try the following questions:
1. Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% dioxygen by mass.
2. Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and the mass per cent of nitric acid in it being 69%.
3. What is the symbol for SI unit of mole? How is the mole defined?
4. The density of 3 molal solution of NaOH is 1.110 g mL–1. Calculate the molarity of the solution.
5. Calculate the mass of ammonia produced if 2.00 × 103 g dinitrogen reacts with 1.00 × 103 g of dihydrogen according to the following chemical equation:
N2(g) + H2(g) → 2NH3(g)