Apentix/AP Chemistry/Unit 8: Acids and Bases/Question
AP Chemistryeasymcq1 pt

Two 0.10 M weak acid solutions are prepared: HA with Ka = 1 × 10⁻⁴ and HB with Ka = 1 × 10⁻⁸. Which solution has the higher pH and why?

A.HA, because the larger Ka releases more protons
B.HB, because the smaller Ka produces fewer protons
C.Both have the same pH because Ka never affects [H⁺]
D.HA, because a smaller Ka means a stronger acid

Explanation

Core Concept

Ka measures how completely an acid donates its proton, and [H⁺] scales with the square root of Ka for a weak acid. With Ka four orders of magnitude smaller, HB generates roughly one hundred times less H⁺ than HA at equal concentration. Fewer protons means less acidity, so the HB solution has the higher pH.

Correct Answer

BHB, because the smaller Ka produces fewer protons

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