Wed January 26, 2011 By: Rishita Gajbhiye

please tell me how to find equivalent mass?explain with eg.and what is normality?

Expert Reply
Wed January 26, 2011

The weight of a substance that will combine with or replace one mole of hydrogen or one-half mole of oxygen. The equivalent weight is equal to the atomic weight divided by the valence.

For example, for the following reaction 

or for the folloing reaction:

Elements may assume different equivalent weights in different compounds. For example, iron (atomic weight 55.845) has equivalent weight 27.9225 if it is valence 2 in the compound (Fe2+); or 18.615 if it is valence 3 (Fe3+).

The equivalent weight can also be computed for other than pure elements. For example, the carbonate radical (CO3) has a formula (atomic) weight of 60.0092 and assumes valence 2 in compounds, so its equivalent weight is 30.0046.


The 'Normality' of a solution is the 'Molarity' multiplied by the number of equivalents per mole (the number moles of hydroxide or hydronium ions per mole)
for the molecule.  For NaOH there is one equivalent per mole (one mole of hydroxide ions release per mole of NaOH dissolved in water) so the 'Normality'
is the 'Molarity' times 1 eq / mole.

We hope that clarifies your query.




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