How to calculate equivalent weight ?

Eequivalent weight Calculations

So, if you want to calculate equivalent weight you must have a clear concept on valency factor which we say n-factor , Equivalent weight of any molecule can be define as Molecular weight divided by n-factor , so let’s understand the meaning of n-factor to have clear idea of calculating the  equivalent weight of any molecules.

Equivalent weight. =  Molecular weight/n-factor

The equivalent of a substance is calculated as

    ∴    Number of equivalents ==

    ∴    Number of equivalents = no. of moles × n factor

n Factor Calculation

Since, equivalent of a substance = and eqv. mass =

Thus, to calculate the equivalents of any substance, the knowledge of n factor calculation is a must. The n factor of various substances is calculated as:

1.    Acids : The number of moles of replaceable H+ ions per mole of the acid i.e. basicity.

For example, HNO₃; n = 1; H₂SO₄; n =2; H₃PO₄; n = 3, H₃PO₃; n = 2, H₃BO₃; n = 1

All these values are the maximum values of n factor for the corresponding acid e.g. the n factor for H₂SO₄ may be 1 or 2 depending on the reaction it undergoes.

H₂SO⁴ + NaOH NaHSO₄ + H₂O        …(i)

H₂SO⁴ + 2NaOH Na₂SO4 + H₂O        …(ii)

For bases: Bases will be treated as species which furnish OH− ions when dissolved in a solvent. The n-factor of a base is the no. of OH− ions that a molecule of the base would give when dissolved in a solvent (Acidity).

For example,  NaOH (n = 1), Ba(OH)₂ (n = 2), Al(OH)₃ (n = 3), etc.

For salts: A salt reacting such that no atom of the salt undergoes any change in oxidation state.

For example,   2AgNO₃  + MgCl₂   Mg(NO₃)2 + 2AgCl

In this reaction, it can be seen that the oxidation state of Ag, N, O, Mg and Cl remains the same even in the product. The n-factor for such a salt is the total charge on cation or anion.

InRedox Change

For oxidizing agent or reducing agent n-factor is the change in oxidation number per mole of the substance.   

SOME OXIDIZING AGENTS /REDUCING AGENTS WITH Equivalent weight