Equivalent Weight
Introduction:
The branch of chemistry which deals with mass relationship in chemical reactions is called stoichiometry. Stoichiometry is the quantitative analysis of various types of chemical reactions. Most of these calculations are done on the basis of mole concept. The term ‘mole’ was first introduced by ‘Ostwald’. It is a Latin version of the term ‘heap’ or ‘pile’ or ‘weight’, which refers the amount of a substance containing a fixed number of its elementary particles equivalent to the Avogadro’s number (6.023 × 1023). In modern practice, it is easy to express the mole of substance in terms of its weight or its volume. The analysis based on weight is called Gravimetric analysis whereas the analysis based on volume is known as volumetric analysis.
Core Concepts
Equivalent weight
The minimum weight of any chemical species, which reacts (completely) or liberates 1 g hydrogen (11.2 litre), 8 g Oxygen (5.6 litre), 35.5 g Chlorine (11.2 litre), 80 g Bromine (11.2 litre), 127 g Iodine (11.2 litre) is called Equivalent weight of that particular chemical species.
| Element |
H | O | Cl | Br | I |
| Atomic wt. | 1 | 16 | 35.5 | 80 | 127 |
| Eq. wt. | 1 | 8 | 35.5 | 80 | 127 |
The above definition for equivalent weight is not sufficient. For example if an acid is given then the equivalent weight of an acid is defined as the ratio of Molecular weight of acid to its basicity.
Basicity means number of acidic hydrogens present in the molecule.
Acidic hydrogen means hydrogen atoms directly attached to electronegative element.
