Questions: Nonaqueous Solvents, the Leveling Effect, and Superacids
4 questions to test your understanding
Score: 0 / 4
Question 1 Multiple Choice
Why do HCl and HClO₄ show the same acid strength in dilute aqueous solution?
AThey have identical Ka values in every solvent
BWater is basic enough to ionize both completely, so both are leveled to H₃O⁺
CBoth are diprotic acids
DTheir conjugate bases have the same size
Any acid stronger than H₃O⁺ transfers its proton to water essentially completely. The acid that actually remains in solution is H₃O⁺ in both cases, so their intrinsic difference is hidden.
Question 2 True / False
Acetic acid, a weak acid in water, behaves as a strong acid in liquid ammonia.
TTrue
FFalse
Answer: True
Ammonia is a much stronger base than water. It accepts protons from acetic acid essentially completely, so acetic acid is leveled to NH₄⁺, the strongest acid that can exist in liquid ammonia.
Question 3 Multiple Choice
In liquid ammonia, which species is the strongest base that can exist in the solvent?
AOH⁻
BNH₄⁺
CNH₂⁻
DNH₃
Liquid ammonia autoionizes as 2NH₃ ⇌ NH₄⁺ + NH₂⁻. Any base stronger than the amide ion would deprotonate ammonia and be leveled to NH₂⁻.
Question 4 Short Answer
What is a superacid, and why are superacids useful to chemists?
Think about your answer, then reveal below.
Model answer: A superacid is a medium more acidic than 100% sulfuric acid, such as HSO₃F–SbF₅ (magic acid) or HF–SbF₅. They can protonate very weak bases, including hydrocarbons, and keep carbocations long-lived enough to study.
George Olah used superacid media to observe carbocations directly by NMR, work recognized with the 1994 Nobel Prize in Chemistry. Such media lie far beyond the acidity window of water.