Understanding Acid Strength: Nitric Acid vs Phosphoric Acid

Which acid is considered a strong acid and which one is a weak acid?

1. Nitric acid is a strong acid.

2. Phosphoric acid is a weak acid.

Answer:

The correct statement that describes the relationship between nitric acid and phosphoric acid is: The pKA of nitric acid is lower than the pKA of phosphoric acid.

The pKa value of an acid is a measure of its ability to donate protons (H+ ions) in a solution. Specifically, it is the negative logarithm (base 10) of the acid's dissociation constant (Ka). A lower pKa indicates a stronger acid, while a higher pKa indicates a weaker acid. So the pKa of phosphoric acid is lower than the pKa of nitric acid.

Explanation: Phosphoric acid is considered a weak acid, while nitric acid is categorized as a strong acid. This distinction is due to the differences in their acid dissociation constants (Ka) and pKa values. The pKa value is a measure of the tendency of an acid to donate a proton (H+) in an aqueous solution. A lower pKa indicates a stronger acid, as it readily donates protons.

Nitric acid has a lower pKa compared to phosphoric acid. This implies that nitric acid is more likely to dissociate and release H+ ions in solution. The lower pKa value signifies that the equilibrium between the undissociated acid and its ions lies more towards the ionized form in the case of nitric acid. On the other hand, phosphoric acid's higher pKa suggests that it is less likely to dissociate and donate protons, making it a weaker acid.

This trend in pKa values aligns with the relative strengths of these acids. Nitric acid's lower pKa indicates its strong acidic nature, while phosphoric acid's higher pKa corresponds to its weaker acidic behavior. Therefore, the statement that the pKa of phosphoric acid is lower than the pKa of nitric acid is accurate.