Normality:  

It is defines as the number of gram equivalents of solute present per litre of solution. It is denoted by ‘N’.  

Normality (N) = Number of gram equivalents of solute/Number of litres of the solution

or Normality × Number of llitres of the solution = Number of gram equivalents of the solute  

Let wA gram of the solute of equivalent mass EA be present in V litres of the solution, then,    

Normality = wA/EA/V = wA/EA×V

Normality × Equivalent mass – wA/V  

= Strength of the solution g/L.                

Solutions are expressed as    

1 N, 2 N, N/2, N/10, N/100, N/1000 etc.    

1N = Normal  

= One gram equivalent of the solute per litre of solution  

= Normality is 1  

N/2 = Seminormal  

= 0.5 g equivalent of the solute per litre of solution  

= Normality is 0.5  

N/10 = Decinormal  

= 0.1 g equivalent of the solute per litre of solution  

= Normality is 0.1  

N/100 = Centinormal  

= 0.01 g equivalent of the solute per litre of solution  

= Normality is 0.01  

N/1000 = Millinormal  

= 0.001 g equivalent of the solute per litre of solution  

= Normality is 0.001

Relationship between normality and molarity:  

We know that  

Molarity × Molecular mass = Strength of solution (g/L)  

Similarly,  

Normality × Equivalent mass = Normality of the solution (g/L)  

Hence,  

Molarity × Molecular mass = Normality × Equivalent mass    

or Normality/Molarity = Molecular mass/Equivalent mass = n

So, Normality = n × Molarity  

[Normailty (second method): Let ‘d’ is the density of solution in g/mL and x is the percentage of the solute by mass.  

Then,  

          N = x×d×10/Equivalent mass of solute

Formality:  

It is the number of formula mass in grams present per litre of solution. In case formula mass is equal to molecular mass, formality is equal to molarity. Like molarity and normality, the formality is also dependent on temperature. It is used for ionic compounds in which there is no existence of molecule. Mole of ionic compounds is called formole and molarity as formality.

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