Question 14.1: EXPLAINING ACIDITY WITH THE ARRHENIUS AND BRØNSTED–LOWRY THE...
EXPLAINING ACIDITY WITH THE ARRHENIUS AND BRØNSTED–LOWRY THEORIES
Account for the acidic properties of nitrous acid (HNO_{2}) using the Arrhenius theory and the Brønsted–Lowry theory, and identify the conjugate base of HNO_{2}.
STRATEGY
To account for the acidity of a substance, consider how it can produce H^{+} ions in water (Arrhenius theory) and how it can act as a proton donor (Brønsted–Lowry theory).

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HNO_{2} is an Arrhenius acid because it dissociates in water to produce H^{+} ions:
HNO_{2}(aq) \rightleftharpoons H^{+}(aq) + NO_{2}^{-}(aq)Nitrous acid is a Brønsted–Lowry acid because it acts as a proton donor when it dissociates, transferring a proton to water to give the hydronium ion, H_{3}O^{+}:
\underbrace{\underset{Acid}HNO_{2}(aq) + \underbrace{\underset{Base}{H_{2}O(l)} \rightleftharpoons \underset{Acid}{H_{3}O^{+}(aq)} }_{Conjugate acid–base pairs} + \underset{Base}{NO_{2}^{-}(aq)}} _{}The conjugate base of HNO_{2} is NO_{2}^{-}, the species that remains after HNO_{2} has lost a proton.