What is the Normality of concentrated (18 M) sulfuric acid (H2S04) ?
The correct answer and explanation is:
Correct Answer: 36 N
Explanation (300 words)
Normality (N) is a measure of concentration equivalent to the molarity (M) multiplied by the number of reactive equivalents per mole of solute. For acids, this number is determined by the number of replaceable hydrogen ions (H⁺) that an acid molecule can donate in a reaction.
Sulfuric acid (H₂SO₄) is a diprotic acid, meaning each molecule can donate two protons (H⁺) in aqueous solution: H2SO4→2H++SO42−\text{H}_2\text{SO}_4 \rightarrow 2\text{H}^+ + \text{SO}_4^{2-}
Therefore, 1 mole of H₂SO₄ provides 2 equivalents of H⁺.
The relationship between molarity (M) and normality (N) is given by: Normality=Molarity×n\text{Normality} = \text{Molarity} \times \text{n}
Where:
- Molarity (M) = 18 M (concentration of pure sulfuric acid)
- n = 2 (number of replaceable H⁺ ions per molecule of H₂SO₄)
Normality=18 mol/L×2=36 N\text{Normality} = 18\ \text{mol/L} \times 2 = \boxed{36\ \text{N}}
Why This Matters
Normality is particularly useful in acid-base titrations and reactions involving ionic transfers because it directly measures reactive capacity. While molarity tells how many moles of substance are present, normality reflects the substance’s chemical reactivity in a given reaction.
For example, in titration calculations where H₂SO₄ is reacting with a base (like NaOH), using normality simplifies the math, since it automatically accounts for the two H⁺ ions H₂SO₄ can donate.
Hence, concentrated sulfuric acid, which is 18 M, has a normality of 36 N due to its ability to donate 2 moles of H⁺ per mole of acid.