CourseCourseConceptConceptDocsDocuments

IB Chemistry HL 3.2.1 Oxidation and Reduction Questions

Use real HL exam questions to track oxidation-state and electron changes, identify redox agents and interpret redox equations.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Identify oxidation or reduction from oxidation-state changes, electron loss or gain, and oxygen/hydrogen changes in the stated species.
  • Identify the oxidizing and reducing agents and the species oxidized or reduced, justifying each assignment from the redox change.
  • Write or interpret redox and disproportionation equations and distinguish redox reactions from non-redox reaction types using the reactants and products.

Learn this topic

Study 3.2.1—Oxidation and reduction conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Chemistry HL 3.2.1 Oxidation and Reduction Questions question 1

[Maximum number: 3]

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula PH3\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:

P4( s)+3OH−(aq)+3H2O(l)→PH3( g)+3H2PO2−(aq)\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})

Oxidation is now defined in terms of change of oxidation number. Explore how earlier definitions of oxidation and reduction may have led to conflicting answers for the conversion of P4\mathrm{P}_{4} to H2PO2−\mathrm{H}_{2} \mathrm{PO}_{2}^{-}and the way in which the use of oxidation numbers has resolved this.

All question bank results loaded