A student dissolves the same number of moles of sulfuric acid and carbonic acid separately in equal volumes of water. Both solutions have the same concentration. Describe and explain the differences you would expect to observe in the pH values of the two solutions and in the rate at which each solution reacts with magnesium ribbon.

Sulphuric acid gives a lower pH than carbonic acid at the same concentration.

Sulphuric acid is a strong acid; it dissociates completely in water to give 2 H⁺ and SO₄²⁻, so the [H⁺] equals the acid concentration.

Carbonic acid is a weak acid; it only partially dissociates (H₂CO₃ ⇌ H⁺ + HCO₃⁻), so the [H⁺] is much lower than the acid concentration.

Because the [H⁺] is higher, the sulphuric acid solution reacts faster with magnesium ribbon. The high proton concentration gives a greater frequency of successful collisions between H⁺ and Mg, accelerating the reaction.

Thus the sulphuric acid solution has a lower pH and reacts more rapidly with magnesium than the carbonic acid solution.