We define normality as the number of grams equivalent to solute that is present in a one-liter solution. So, the unit of normality is gram/liter.
We denote normality with the letter ‘N’.
We can write the Normality Formula as:
Now, you might be wondering what gram equivalent is and how it is related to the number of moles.
Let’s understand what is equivalent and its significance as well.
Let’s say we have an equation:
NaCl + H2SO4 → Na2SO4 + HCl
(Sodium Chloride) (Sulphuric Acid) (Sodium Sulfate) (Hydrochloric Acid)
You can see that this equation is not balanced. Now, let’s balance this equation:
2NaCl + H2SO4 → Na2SO4 + 2HCl
No of moles (n): (2 moles) (1 mole) (1 mole) (2 moles)
So, 2 moles of NaCl react with 1 mole of H2SO4 to give 1 mole of Na2SO4 and 2 moles of HCl.
This means, without balancing the equation, we can’t determine the quantity of reactant (or moles) that undergoes a reaction to form a product.
Number of Gram Equivalent
So, let’s get forward with understanding the concept of gram equivalence.
We know that no of moles = Mass/Molecular weight
Number of gram equivalent = Mass/Equivalent weight,
and Equivalent weight = Molecular weight X
(X = valence factor, where valence factor for acids and bases is the number of H+ and OH- ions they release in the solution, respectively).
We’ll understand these two formulas with an example.
Let’s find out Gram Equivalent
For example, Find the number of gram equivalents present in 0.5 g of HCl.
HCl releases one H+ ion in the solution, so its valence factor = 1.
The molecular weight of HCl = 36.46 g.
So, equivalent weight =
Molecular weight X = 36.46/1 = 36.46 g, and
Number of gram equivalent
= Mass/Equivalent weight
= 0.5/36.46 = 0.0137
So, we get the number of gram equivalent = 0.0137
Let us take another example of 1.06 g of Na2CO3 to understand this concept clearly
We are given the mass of Na2CO3 = 1.06 g.
Firstly, Find the equivalent weight of Na2CO3.
Since Na2CO3 is a salt, so the number of positive charges on the cation gives X = 2
Molecular weight = 106 g
So, Equivalent Weight =
= 106/2 = 53 g,
and number of gram equivalent is:
= 1.06/53 = 0.02
In a chemical equation, the number of grams equivalent of both reactions always remains the same.
There are three types of Normality
Seminormal - The solutions whose normality is ½ or N/2.
Binormal - The solutions having normality as 2 or 2 N.
Decinormal - Normality is 1/10 or N/10.
CentiNormal - Normality is 1/100 or N/100.
Normality Calculation Formula
Let’s take an example of how to calculate normality:
If 13 g of N2O4 is present in 500 ml of solution. Find normality.
We are given a mass of N2O4 = 0.65 g, and volume = 500 ml = 0.5 l.
We know that normality, N = no of gram equivalent/volume of solution in liters
Let’s find out equivalent weight to find out the number of gram equivalent for N2O4
Molecular weight of N2O4 = (2 x 14) + (4 x 16) = 28 + 64 = 92 g.
Since the number of negative charges on oxygen = 4. So, X = 4
So, equivalent weight = Molecular weight X = 92/4 = 13 g,
and Number of gram equivalent =
= 13/13 = 1
Now, let’s calculate the normality, by the formula given below:
N = No of gram equivalent / Volume of solution in liters = 1/0.5
N = 2 gram / liter.
Here, the Normality is N = 2, which means the solution of N2O4 is BiNormal.
For deriving the normality equation, let’s understand normality in mixtures
Let’s consider two ideal solutions having their normalities as Na and Nb, and the volume as Va and Vb respectively as shown below:
Where Na = The normality of the acidic solution,
Va = Volume of the acidic solution,
Nb = Normality of the basic solution, and
Vb = Volume of the basic solution.
(Image Will Be Updated Soon)
(Image Will Be Updated Soon)
On combining these two solutions, we get a mixture whose volume is Va + Vb and the normality as N.
So, we got the Normality Formula for the mixture as:
N = (Na Va + Nb Vb)/ (Va + Vb)
Let’s consider three Cases:
Case 1: The concentration of the acidic solution > concentration of the basic solution (the release of H+ ions > OH- ions)
So, Na Va > Nb Vb
Case 2: The concentration of the basic solution < acidic solution, then
Na Va < Nb Vb (release of OH- ions > H+ ions)
Case 3: When concentration is equal, then
Na Va = Nb Vb is the normality equation.
In this case, there is no release of both OH- ions and H+ ions.
This means the number of gram equivalent of H+ ions = the number of gram equivalent of OH- ions. Such a type of solution is neutral and this process is called neutralization.
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