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What does measuring the pH of a weak acid solution of known concentration reveal?
AThat the acid has fully ionized
BThat the acid has not ionized at all
CThat only a fraction has ionized
DThat the acid has decomposed fully
Answer & Solution
Correct answer: C. That only a fraction has ionized
1. The concentration tells you how much acid was added to the solution.
2. The pH tells you how much hydronium ion is actually there.
3. For a weak acid the second is far smaller than the first would suggest.
4. That gap shows only a fraction of the acid is ionized at any moment.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section The Ionization of Weak Acids and Weak Bases_
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