IB Chemistry HL 3.1.3 Amphiprotic Species Questions

Use real HL exam questions to identify amphiprotic species and write paired proton-transfer equations for both roles.

Exam points

Identify an amphiprotic species that can donate and accept a proton.
Write two balanced equations showing the species acting as a Brønsted–Lowry acid and as a base.
Use the ability to form both protonated and deprotonated products to justify amphiprotic behaviour.

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Study 3.1.3—Amphiprotic species conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula $\mathrm{PH}_{3}$ .

Phosphine is usually prepared by heating white phosphorus, one of the allotropes of phosphorus, with concentrated aqueous sodium hydroxide. The equation for the reaction is:

\mathrm{P}_{4}(\mathrm{~s})+3 \mathrm{OH}^{-}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{PH}_{3}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})

The ion $\mathrm{H}_{2} \mathrm{PO}_{2}^{-}$ is amphiprotic. Outline what is meant by amphiprotic, giving the formulas of both species it is converted to when it behaves in this manner.

can act as both a «Brønsted-Lowry» acid and a «Brønsted-Lowry» base OR can accept and/or donate a hydrogen ion/proton/ $\mathrm{H}^{+}$ $\mathrm{HPO}_{2}{ }^{2-}$ AND $\mathrm{H}_{3} \mathrm{PO}_{2}$

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IB Chemistry HL 3.1.3 Amphiprotic Species Questions question 1