Mole : One mole is the amount of a substance which contains 6.022 x 1023 constituent particles of the substance. These particles may be atoms, molecules or ions.
One mole can also be defined as the amount of a substance which contains as many particles as the number of C-12 atoms in its 12 g mass.
The number 6.022 x 1023 is called Avogadro number or constant and it is denoted by N or NA i.e. NA = 6.022 x 1023
Atomic Mass Unit(amu) : In Chemistry, we have to make calculations with extremely small and big numbers especially the mass of an atom.
Molar Mass : The mass of one mole of a substance is called its molar mass.
Ex: Molar mass of CaCO3 = 100g
Molar mass of Na atom = 23 g
Molar mass of Na+ ion = 23 g
Percentage Composition: As we know that each element of a compound holds a fixed percentage by mass.
% of an element = Mass of an element × 100/Molecular or Formula mass of the compound
Empirical formula : The empirical formula of a compound represents simplest whole number ratio of atoms present in it. Ex: The empirical formula of Benzene(C6H6) is CH.
Molecular formula : The molecular formula of a compound represents the actual number of atoms present in the compound. Ex: The molecular formula for Benzene is C6H6.
Key Point : Molar mass = Empirical formula mass x n
Stoichiometry : The study of calculations on the basis of chemical reactions is called stoichiometry.
We can get a lot of information from an equation of a chemical reaction. Consider a chemical equation or reaction :
2H2 (g)+ O2 (g)→2H2O (g)
We can make following observations:
I. 2 moles of H2 react with 1 mole of O2 to produce 2 moles of water.
II. 2 molecules of H2 reacts with 1 molecule of O2 to produce 2 molecules of water.
III. 44.8 L of H2 react with 22.4 L of O2 to produce 22.4 L of water vapours.
IV. 4 g of H2 react with 32 g of O2 to produce 36 g of water vapours.
Limiting Reagent : In a chemical reaction, the reactant which is present in the lesser amount is called the limiting reagent. In actual, a limiting reagent controls the reaction as no reaction takes place after it is consumed.
Ex : Let us take 2 g hydrogen and 20 g oxygen to form water.
According to the reaction 2H2 + O2 →2H2O
We know that 4 g of hydrogen requires 32 g of oxygen to form water which means that 2 g of hydrogen will react with 16 g of oxygen. So, 4 g oxygen will be left unreacted. It’s obvious that hydrogen is the limiting reagent.