For a monoprotic acid, normality is equal to molarity because each molecule provides one reactive unit.

For a monoprotic acid, normality is equal to molarity because each molecule provides one reactive unit.

• A. Normality equals molarity
• B. Normality is twice molarity
• C. Normality is quarter molarity
• D. Normality is unrelated to molarity

Answer: (A)

Normality measures the number of reactive units (equivalents) per liter. For an acid, that reactive unit is the proton it can donate. In a monoprotic acid, each molecule donates exactly one proton, so one mole yields one equivalent. That makes the normality equal to the molarity, because the amount of reactive capacity per liter is the same as the amount of substance per liter. For example, a 0.10 M solution of a monoprotic acid has 0.10 equivalents per liter, i.e., 0.10 N. This parity can differ for polyprotic acids, where each molecule can donate more than one proton. For instance, a diprotic acid provides two protons per molecule, so its normality would be twice its molarity in terms of H+ equivalents. But for monoprotic acids, normality and molarity match.

Normality measures the number of reactive units (equivalents) per liter. For an acid, that reactive unit is the proton it can donate. In a monoprotic acid, each molecule donates exactly one proton, so one mole yields one equivalent. That makes the normality equal to the molarity, because the amount of reactive capacity per liter is the same as the amount of substance per liter. For example, a 0.10 M solution of a monoprotic acid has 0.10 equivalents per liter, i.e., 0.10 N.

This parity can differ for polyprotic acids, where each molecule can donate more than one proton. For instance, a diprotic acid provides two protons per molecule, so its normality would be twice its molarity in terms of H+ equivalents. But for monoprotic acids, normality and molarity match.