How many moles of benzoic acid, a monoprotic acid with K_a = 6.4 *10^-⁵, must be dissolved in 500. mL of H₂O to produce a solution with pH = 2.50?

Question

Quizplus · Accepted Answer

To find the moles of benzoic acid needed, use the formula for pH and the expression for the dissociation of a weak acid. The concentration of H⁺ ions is 10^-2.50 M. Using the formula Ka = [H⁺][A⁻]/[HA], and solving for [HA], we find that the concentration of benzoic acid needed is approximately 0.078 M. Multiplying by the volume (0.5 L) gives 0.039 moles, which corresponds to choice C.

How Many Moles of Benzoic Acid, a Monoprotic Acid with Ka

How Many Moles of Benzoic Acid, a Monoprotic Acid with K_a