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.

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 $\dfrac{10^{-2}}{2} = 5 \times 10^{-3}\;\text{mol}\cdot\text{dm}^{-3}$ 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.