9701 · 7.2
Brønsted-Lowry theory of acids and bases flashcards
Revision flashcards for Cambridge 9701 Brønsted-Lowry theory of acids and bases (syllabus 7.2). Flip, recall, then mark a real past-paper question.
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What is a Brønsted-Lowry acid?
A species that acts as a proton ($H^+$) donor.
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What is a Brønsted-Lowry base?
A species that acts as a proton ($H^+$) acceptor.
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What is a conjugate acid-base pair?
Two species that differ from each other by a single proton ($H^+$). For example, the acid $HCl$ and its conjugate base $Cl^-$.
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In the reaction $NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$, identify the acid and its conjugate base.
The acid is $H_2O$ (it donates a proton). Its conjugate base is $OH^-$.
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In the reaction $NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$, identify the base and its conjugate acid.
The base is $NH_3$ (it accepts a proton). Its conjugate acid is $NH_4^+$.
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What is the key difference between a strong acid and a weak acid?
A strong acid fully dissociates (ionises) in aqueous solution, while a weak acid only partially dissociates, establishing an equilibrium.
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Which reaction arrow is used to show the dissociation of a strong acid like $HCl$?
A one-way arrow ($→$), indicating the reaction goes to completion. e.g., $HCl(aq) → H^+(aq) + Cl^-(aq)$.
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Which reaction arrow is used to show the dissociation of a weak acid like $CH_3COOH$?
An equilibrium arrow ($⇌$), indicating a reversible reaction where dissociation is incomplete. e.g., $CH_3COOH(aq) \rightleftharpoons H^+(aq) + CH_3COO^-(aq)$.
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What does 'amphiprotic' mean? Give a key example.
A substance that can act as both a Brønsted-Lowry acid and a base. Water ($H_2O$) is the most common example.
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What is the conjugate base of the hydrogensulfate ion, $HSO_4^-$?
The sulfate ion, $SO_4^{2-}$. The $HSO_4^-$ ion donates a proton.
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What is the conjugate acid of the hydrogensulfate ion, $HSO_4^-$?
Sulfuric acid, $H_2SO_4$. The $HSO_4^-$ ion accepts a proton.
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Is ammonia, $NH_3$, a Brønsted-Lowry acid or base?
It is a weak Brønsted-Lowry base because its lone pair of electrons on the nitrogen atom can accept a proton to form the ammonium ion, $NH_4^+$.