Question

What is the normality of 2M solution of phosphoric acid of an acid base titration?

Answer 1

To solve the question we need to understand the concept of Molarity and Normality. Molarity is the number of moles of solute present in a litre of solution. Normality is the number of gram equivalents of solute present in a litre of solution. Both Molarity and Normality are concentration terms.

Complete answer:
Let us first talk about the formulas of Molarity and Normality and the relation between both of these concentration terms-
The formula of Molarity is given as-
$M = \dfrac{n}{V} - - - - (1)$
Here, $n$ is the number of moles of solute which is given as given mass/molar mass and $V$ is the volume of solution in litres
(Always remember that if the volume of solution is in millilitre first convert it into litre by dividing it by 1000)
The formula of Normality is given as-
$N = \dfrac{{grmEq}}{V} - - - - (2)$
Here, $grmEq$ is the number of gram equivalent of solute which is given as-
$grmEq = \dfrac{n}{{Eq.mass}} - - - - (3)$
Here, $n$ is the number of moles of solute and $Eq.mass$ is the equivalent mass which is related to molar mass as follows-
$Eq.mass = \dfrac{M}{x} - - - - (4)$
where $M$ is the molar mass and $x$ is the valency factor which is the measure of basicity of acids, acidity of bases, or total positive and negative charge of salts.
We can convert Molarity into Normality and vice versa using the following equation-
$Normality = Molarity \times x - - - - (5)$
In the question, we are given a 2M solution of Phosphoric acid and we have to find its Normality.
The formula of phosphoric acid is ${H_3}P{O_4}$and it is a tribasic acid i.e. produces 3 Hydrogen ions on dissociation. So the value of $x$ is 3.
Putting both the values in Equation (5) we get-
$Normality = 2 \times 3 = 6N$
So the Normality of a 2M solution of phosphoric acid solution will be equal to 6N.

Note:
It is interesting to note that both Molarity and Normality are dependent on temperature since both contain volume terms in the formula. The concept of Normality and Molarity is highly useful in chemical laboratories to measure the concentration of solutions. These are useful in redox reactions, precipitation reactions, acid-base chemistry, and several types of titrations.