Problem 4.4: The chapter distinguishes pH from alkalinity

From Chapter 4 Problem Set. Level 1: Conceptual Mastery.

Question

The chapter distinguishes pH from alkalinity: “pH describes the current intensity of equilibrium. Alkalinity describes the future capacity to resist change.” Why is this distinction important?

Answer

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pH tells you the current hydrogen concentration: the intensity right now. Alkalinity tells you how much acid the water can absorb before the pH moves significantly. A high-pH solution with little buffering capacity can shift sharply when acid is added, while a moderately alkaline solution with strong bicarbonate buffering can resist change. They are functionally different.