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NSWChemistryQuick questions
Module 5: Equilibrium and Acid Reactions
Quick questions on Brønsted-Lowry acid-base theory explained: HSC Chemistry Module 5
12short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is definitions?Show answer
The definition focuses on the proton transfer itself, not on whether the reaction occurs in water.
What is conjugate acid-base pairs?Show answer
When an acid donates a proton, it becomes a base (because it can now accept the proton back). When a base accepts a proton, it becomes an acid. The acid and base that differ by a single $H^+$ form a conjugate acid-base pair.
What is amphiprotic species?Show answer
An amphiprotic species can act as either a Brønsted-Lowry acid or a Brønsted-Lowry base depending on what it reacts with. The most important examples:
What is comparison with Arrhenius theory?Show answer
Arrhenius (1887): an acid produces $H^+$ in water, a base produces $OH^-$ in water.
What is water?Show answer
- Acts as a base: $H_2O + HCl \rightleftharpoons H_3O^+ + Cl^-$. - Acts as an acid: $H_2O + NH_3 \rightleftharpoons OH^- + NH_4^+$.
What is bicarbonate ion?Show answer
- Acts as a base: $HCO_3^- + H_3O^+ \rightleftharpoons H_2CO_3 + H_2O$. - Acts as an acid: $HCO_3^- + OH^- \rightleftharpoons CO_3^{2-} + H_2O$.
What is hydrogen sulfate ion?Show answer
Similarly acts as both an acid and a base.
What is forward direction?Show answer
- Water loses a proton (becomes $OH^-$). So $H_2O$ is the acid. - Ammonia gains a proton (becomes $NH_4^+$).
What is reverse direction?Show answer
- The $NH_4^+$ ion donates a proton, so it is the conjugate acid of $NH_3$. - The $OH^-$ ion accepts a proton, so it is the conjugate base of $H_2O$.
What is mixing up the conjugate?Show answer
The conjugate base is the acid minus $H^+$. The conjugate acid is the base plus $H^+$. Differ by one proton, never more.
What is confusing amphiprotic with amphoteric?Show answer
Amphiprotic is the proton-specific subset of amphoteric. For HSC, use amphiprotic when discussing $H_2O$, $HCO_3^-$, and amino acids.
What is forgetting state symbols?Show answer
Acid-base reactions in HSC answers are expected to have $(aq)$ or $(l)$ on every species.