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Module 6: Acid/Base Reactions
Quick questions on Properties of acids and bases (Arrhenius model) explained: HSC Chemistry Module 6
9short 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 indicators?Show answer
An indicator is a weak acid or weak base whose protonated and deprotonated forms have different colours. The colour change occurs across a narrow pH range, usually about 2 pH units wide.
What is the Arrhenius model?Show answer
Svante Arrhenius (1887) proposed that acids and bases are substances that ionise in water.
What is historical development?Show answer
The Arrhenius model built on earlier ideas:
What is limitations of the Arrhenius model?Show answer
Arrhenius works well for simple aqueous acid-base reactions, but it cannot explain:
What is calling ammonia an Arrhenius base?Show answer
It is not. Ammonia is a Bronsted-Lowry base because it accepts a proton from water: $NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$. The $OH^-$ comes from the water, not from $NH_3$ itself.
What is forgetting state symbols?Show answer
Acid-base equations are expected to carry $(aq)$ or $(l)$ on every species.
What is treating the model as wrong, rather than limited?Show answer
Arrhenius is correct for aqueous, ionic acids and bases. It is a special case of the broader Bronsted-Lowry model. Markers want "limited" not "incorrect".
What is confusing strength and concentration?Show answer
A property like "turns blue litmus red" depends on $[H^+]$, which is set by both the strength (degree of ionisation) and the concentration. Cover this carefully on the strong vs weak page.
What is listing taste or feel as a test?Show answer
Never test laboratory chemicals by taste or touch. State the property but not the procedure.