Equivalent mass

It is the mass of an element or a compound which would combine with or displace (by weight) 1 part of hydrogen or 8 parts of oxygen or 35.5 parts of chlorine

Eq. wt. of metal = wt. of metal / wt. of H2 displaced * 1.008

= wt. of metal / volume of H2 (in mL) displaced at STP * 11200

Eq. wt. of metal = wt. of metal / wt. of oxygen combined * 8

= wt. of metal / wt. of chlorine combined * 35.5

In general,

Wt. of substance A / Wt. of substance B = Eq. wt. of A / Eq. wt. of B

or for a compound (I) being converted into another compound (II) of same metal

Wt. of compound I / Wt. of compound II

= eq. wt. of metal + eq. wt. of anion of compound I / eq. wt. of metal + eq. wt. of anion of compound II

Eq. mass 0f a salt = formula mass / total positive or negative charge

Equivalent mass = atomic mass or Molecular mass / n factor

n factor for various compounds can be obtained as

(i) n factor for acids i.e., basicity

(Number of ionisable H+ per molecule is the basicity of acid.)

(ii) n factor for bases, i.e., acidity.

(Number of ionisable OH– per molecule is the acidity of a base.)

(iii) In case of ions, 11 factor is equal to charge of that ion.

(iv) In redox titrations, 11 factor is equal to change in oxidation number.

Equivalent mass of organic acid (RCOOH) is calculated by the following formula

Eq. wt. of silver salt of acid (RCOOAg) / Eq. wt. of Ag(or 108) = Vt. of silver salt / Wt. of silver