Why does hydrochloric acid have a lower pH than ethanoic acid at the same concentration?
Answer and explanation
Correct answer: It ionises almost completely in water
The governing concept is acid strength and hydrogen-ion concentration. Hydrochloric acid is a strong acid, so at the same formal concentration it ionises almost completely in water and produces a relatively high concentration of H⁺ or H₃O⁺ ions. Ethanoic acid is weak and ionises only partially, so it produces fewer hydrogen ions. Since pH = −log[H⁺], a greater hydrogen-ion concentration gives a lower pH. Thus option B is correct; the other statements contradict the properties of these acids.
Frequently asked questions
What is the correct answer to this question?
It ionises almost completely in water
Why is this the correct answer?
The governing concept is acid strength and hydrogen-ion concentration. Hydrochloric acid is a strong acid, so at the same formal concentration it ionises almost completely in water and produces a relatively high concentration of H⁺ or H₃O⁺ ions. Ethanoic acid is weak and ionises only partially, so it produces fewer hydrogen ions. Since pH = −log[H⁺], a greater hydrogen-ion concentration gives a lower pH. Thus option B is correct; the other statements contradict the properties of these acids.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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