# 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

 Species Changed to Reaction Electrons exchanged or change in O.N. Eq. wt. MnO4-(O.A.) Mn2+ in acidic medium MnO4- + 8H+ +5e- →Mn2++ 4H2O 5 MnO4-(O.A.) MnO2 in neutral medium MnO4- + 3e- +2H2O→ MnO2 + 4OH- 3 MnO4-(O.A.) MnO4 2- in basic medium MnO4- + e- → MnO42- 1 Cr2O72-(O.A.) Cr3+ in acidic medium Cr2O72- +14H++6e → 2Cr3+ + 7H2O 6 MnO2(O.A.) Mn2+ in acidic medium MnO2 + 4H++2e-→Mn2+ +2H2O 2 Cl2(O.A.) (in bleaching powder) Cl-Cl- Cl2 + 2e- →2Cl- 2 Species Changed to Reaction Electrons exchanged or change in O.N. Eq. wt. CuSO4(O.A.) (in iodometric titration) Cu+ Cu2+ +e- → Cu+ 1 S2O32-(R.A.) S4O62- 2S2O32- → S4O62- +2e- 2 (for two molecules) H2O2(O.A.) H2O H2O2 +2H+ +2e-→2H2O 2 H2O2(R.A.) O2 H2O2 →O2 +2H+ + 2e-(O. N. of oxygen in H2O2 is −1 per atom) 2 Fe2+(R.A.) Fe3+ Fe2+ → Fe3+ +e- 1 