What is the normality of a 1 M solution of H3PO4

The correct option is 3.0 N.

To understand why this is the correct answer, let's break down the relationship between molarity and normality for acids.

1. Definition of Normality and Molarity:
Molarity ($M$) is defined as the number of moles of solute dissolved per liter of solution.
Normality ($N$) is defined as the number of gram equivalents of solute dissolved per liter of solution.

2. The Relationship Between Normality and Molarity:
For an acid, normality and molarity are related by the following formula:
$\mathrm{Normality}=\mathrm{Molarity}\times \mathrm{Basicity}$
Here, basicity (or n-factor) is the number of replaceable hydrogen ions ($H^{+}$) that one molecule of the acid can donate in an aqueous solution.

3. Determining the Basicity of Phosphoric Acid ($H_3{\mathrm{PO}}_4$):
Phosphoric acid ($H_3{\mathrm{PO}}_4$) is a tribasic acid. Its chemical structure features three hydroxyl ($–\mathrm{OH}$) groups attached to the central phosphorus atom. All three of these hydrogen atoms are ionizable:
$H_3{\mathrm{PO}}_4\to 3H^{+}+{\mathrm{PO}}_4^{3-}$
Since one mole of $H_3{\mathrm{PO}}_4$ releases three moles of $H^{+}$ ions, its basicity (or n-factor) is $3$.

4. Calculating the Normality:
Given that the molarity ($M$) of the solution is $1\text{M}$ and the basicity is $3$, we substitute these values into our relationship formula:
$\mathrm{Normality}=1\times 3=3\text{N}$
Therefore, a 1 M solution of phosphoric acid is 3.0 N.