Understanding The Equivalent Mass of Base in Detail

Equivalent mass means the mass of one equivalent of a substance, that is, the mass of the given substance which combine with a fixed quantity of another substance (for elements, it usually 1.008 gram of hydrogen or 8.0 grams of Oxygen), or we can also define it as the quotient obtained when the gram atomic weight of an element is divided by its valency. To make this easier, let’s consider an example of an element. Say, the Oxygen atomic weight of oxygen is 16, whereas its valence is 2, so we can say that its equivalent mass is 16g2 which is 8 g.

This same principle is applied in the case of acid, bases, oxidizing agents etc.

Then What Is The Equivalent Mass of Base?

The equivalent mass of a base is the number of parts by mass of the base, or it can also be defined as the mass of the base, which contains one gram equivalent of the hydroxyl radical.

Thus the equivalent mass of a base depends on the number of hydroxyl radicals it contains per mole. A number of hydroxyl radicals present in a molecule of a base are represented as the acidity of the given base.

Therefore equation for the equivalent mass of a base can be represented as;

equivalent mass of the base=molecular mass of a base /number of hydroxyl radicals present

Let’s understand in detail with an example;

Example 1: Find the Equivalent mass of the base NaOH.

Ans: Molecular mass of NaOH = 23+ 16+ 1=40

equivalent mass of the base=molecular mass of a base /number of hydroxyl radicals present

equivalent mass of NaOH=40/1=40g

So, in this example, you must have noticed that the molecular mass and the equivalent mass calculated of the given base that is NaOH is the same. This is because the hydroxyl radical group in the given base is one (as you can see, there is only one OH in the given compound)

Let’s consider another example with more hydroxyl radicals

Example 2: Find the Equivalent mass of the base Ca(OH)2.

Ans: Molecular mass of Ca(OH)2=40+16+1×2=74

equivalent mass of the base=molecular mass of a base /number of hydroxyl radicals present

Equivalent mass of Ca(OH)2=74/2=37g.

As you can see, this is a different case where the molecular mass and equivalent mass are different. So they don’t need to be the same in all cases. In this, given an example, there are two hydroxyl groups (that is, two OH groups).

Calculating The Equivalent Mass of Some Acids 

To calculate the equivalent mass of acid is similar to the base. The only difference is in the case of acids: Equivalent mass of acid is represented as the number of parts by mass of the acid, which contains 1.008 parts by mass of replaceable hydrogen atoms. Acids contain one or more replaceable hydrogen atoms. The number of replaceable hydrogen atoms present in an acid molecule is denoted as its basicity.

The equation for calculating eq. mass of an acid

equivalent mass of an acid=Molecular mass of acid /no. of replaceable H

1.Calculate the Equivalent mass of Oxalic acid 

Ans: Molecular mass of oxalic acid( C2H2O4)=(12×2)+(1×2)+(16×4)=90

equivalent mass of Oxalic acid=90/ 2=45

Here, there are two replaceable hydrogens, or the basicity of the acid is 2.

2.Calculate the Equivalent mass of Sulphuric Acid 

Ans:Molecular mass of Sulphuric Acid (H2SO4)=1×2+32+16×4=98

Equivalent mass of Sulphuric acid=98/2=49

   So, in this case, also, the basicity is 2.

3.Calculate the Equivalent mass of Acetic Acid.

Ans:Molecular mass of Acetic Acid

(CH3COOH) =(12×1)+(1×3)+(12×1)+(16+16)+(1×1)=12+3+12+32+1=60    

Equivalent mass of Acetic acid=60/1=60

In this case, there is only one replaceable hydrogen, or we can say basicity is 1.

Conclusion

So, we can conclude by saying that equivalent mass is different from molecular mass as it depends on the presence of hydroxyl or hydronium ions. It is used to compare different chemical compounds and determine the nature of compounds. Equivalent mass of base and acid both can be calculated easily with the above-given formulas, and now you have an idea of what acidity of a base or basicity of acid is.