Consider the following statement : "Acids are substances that dissociate in water to give hydrogen ions H⁺ (aq), and bases are substances that produce hydroxyl ions OH⁻ (aq)." The above statement is based on which one of the following concepts?
- A.Brønsted-Lowry concept
- B.Lewis acid-base concept
- C.Arrhenius concept
- D.Conjugate acid-base concept
Correct answer
Explanation
The correct answer is C, Arrhenius concept. Defining acids and bases by the H⁺ and OH⁻ ions they release in water is exactly the theory Svante Arrhenius gave in 1884.
In the Arrhenius theory, HCl is an acid because it gives H⁺ ions in water, and NaOH is a base because it gives OH⁻ ions. Neutralisation is then simply H⁺ combining with OH⁻ to form water. The theory is limited to aqueous solutions and cannot explain why ammonia, which has no OH group, behaves as a base.
A is wrong because the Brønsted-Lowry concept (1923) defines an acid as a proton donor and a base as a proton acceptor, without needing water.
B is wrong because the Lewis concept defines an acid as an electron-pair acceptor and a base as an electron-pair donor.
D is wrong because conjugate acid-base pairs are part of the Brønsted-Lowry idea, not a separate definition based on H⁺ and OH⁻ in water.
Exam tip: Arrhenius – H⁺/OH⁻ in water; Brønsted-Lowry – proton donor/acceptor; Lewis – electron-pair acceptor/donor.
Practice Questions
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Show answer
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Show answer
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