Calculate The Equivalent Weight of Each of The Following Salts

Calculating the equivalent weight of salts is essential in chemistry for understanding their reactivity and stoichiometric relationships. This guide explains how to determine equivalent weights, provides a calculator for common salts, and discusses practical applications.

What is equivalent weight?

The equivalent weight of a salt is the mass of the salt that provides one gram equivalent of the cation or anion. It's calculated by dividing the molar mass of the salt by the valency of the ion that reacts in the chemical reaction.

For example, sodium chloride (NaCl) has a molar mass of 58.44 g/mol. Since both sodium and chlorine have a valency of 1, the equivalent weight of NaCl is 58.44 g/equiv.

Equivalent Weight Formula:

Equivalent Weight = Molar Mass / Valency

How to calculate equivalent weight

To calculate the equivalent weight of a salt:

Determine the molar mass of the salt using the periodic table
Identify the valency of the ion that reacts in the chemical reaction
Divide the molar mass by the valency to get the equivalent weight

For example, let's calculate the equivalent weight of calcium chloride (CaCl₂):

Molar mass of CaCl₂ = 40.08 (Ca) + 2 × 35.45 (Cl) = 110.98 g/mol
Valency of calcium in this reaction is 2
Equivalent weight = 110.98 / 2 = 55.49 g/equiv

Common salts and their equivalent weights

Here's a table of equivalent weights for common salts:

Salt	Formula	Molar Mass (g/mol)	Valency	Equivalent Weight (g/equiv)
Sodium chloride	NaCl	58.44	1	58.44
Calcium chloride	CaCl₂	110.98	2	55.49
Potassium permanganate	KMnO₄	158.04	5	31.61
Ammonium nitrate	NH₄NO₃	80.04	1	80.04
Ferrous sulfate	FeSO₄·7H₂O	278.0	2	139.0

These values are calculated using the formula: Equivalent Weight = Molar Mass / Valency

Practical applications

The concept of equivalent weight is crucial in several chemical applications:

Titration analysis: Determining the concentration of an unknown solution
Redox reactions: Calculating the amount of substance oxidized or reduced
Neutralization reactions: Calculating the amount of acid or base needed
Precipitation reactions: Determining the amount of precipitate formed

For example, in a titration experiment, knowing the equivalent weight of the titrant allows chemists to calculate the concentration of the unknown solution based on the volume of titrant used.

FAQ

What is the difference between molar mass and equivalent weight?: The molar mass is the mass of one mole of a substance, while the equivalent weight is the mass of the substance that provides one gram equivalent of the reacting ion. For monovalent ions, they are the same.
How do I determine the valency of an ion?: The valency of an ion is determined by its charge. For example, Na⁺ has a valency of 1, Ca²⁺ has a valency of 2, and MnO₄⁻ has a valency of 5.
Can equivalent weight be used for all types of salts?: Yes, the concept of equivalent weight applies to all types of salts, including acids, bases, and salts formed from them. The calculation method remains the same.
What are the limitations of using equivalent weight?: The equivalent weight approach is most useful for reactions involving monovalent ions. For polyvalent ions, it's important to consider the specific valency in the reaction.
How does equivalent weight relate to stoichiometry?: Equivalent weight is directly related to stoichiometry as it helps determine the mole ratio between reactants in a chemical reaction, which is fundamental to stoichiometric calculations.