Question

Calculate the molarity of the acid solution.
H2SO4(aq) with a pH of 2.

Answer 1

Concentration "molarity" of H₂SO₄ in this solution:

5 × 10⁻³ mol / dm³.

Step-by-step explanation

What's the concentration of H⁺ ions in this solution?

`[\text{H}^(+)] = 10^{-\text{pH}}`,

where
`[\text{H}^(+)]` is in the unit mol / dm³.

`\text{pH} = 2`

`[\text{H}^(+)] = 10^(-2) \;\text{mol}\cdot\text{dm}^(-3)`.

What's the concentration "molarity" of H₂SO₄ in this solution?

Sulfuric acid H₂SO₄ is a strong acid. Note the subscript "2". Each mole of this acid dissolves in water to produce two moles of H⁺ ions. It takes only
`(10^(-2))/(2) = 5 * 10^(-3)\;\text{mol}\cdot\text{dm}^(-3)` of H₂SO₄ to produce twice as much H⁺ ions.

As a result, the molarity of H₂SO₄ is 5 × 10⁻³ mol / dm³ or 0.005 M.