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IB Chemistry HL 3.2 Electron Transfer Reactions Question Bank

Practise IB Chemistry HL 3.2 with SL and HL questions on redox cells, E° data, electrolysis, electroplating and ΔG° calculations.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Covered syllabus points

3.2.1—Oxidation and reduction3.2.2—Half-equations3.2.3—Periodic trends in redox3.2.4—Acids with reactive metals3.2.5—Electrodes in electrochemical cells3.2.6—Primary (voltaic) cells3.2.7—Secondary (rechargeable) cells3.2.8—Electrolytic cells3.2.9—Oxidation of organic functional groups3.2.10—Reduction of organic functional groups3.2.11—Reduction of unsaturated compounds3.2.12 (HL)—Standard electrode potential (E⦵)3.2.13 (HL)—Standard cell potential (E⦵cell)3.2.14 (HL)—Gibbs energy and cell potential3.2.15 (HL)—Electrolysis of aqueous solutions3.2.16 (HL)—Electroplating

3.2 Electron transfer reactions 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.

3.2 Electron transfer reactions question 2

[Maximum number: 11]

Bleaches in which chlorine is the active ingredient are the most common, although some environmental groups have concerns about their use.

Question (a)

(a)

Outline, with the help of a chemical equation, why this reaction occurs.

[ 2 ]

Question (b)

(b)

Aqueous sodium chlorate(I), NaOCl, the most common active ingredient in chlorine based bleaches, oxidizes coloured materials to colourless products while being reduced to the chloride ion. It will also oxidize sulfur dioxide to the sulfate ion.

[ 6 ]

Question (i)

(i)

Deduce a balanced equation for the reaction between the chlorate(I) ion and sulfur dioxide from the appropriate half-equations.

[ 4 ]

Question (ii)

(ii)

State the initial and final oxidation numbers of both chlorine and sulfur in the final equation.

Table for Question (ii) — IB Chemistry HL
[ 2 ]

Question (c)

(c)

The standard electrode potential for the reduction of the chlorate(V) ion to the chloride ion is +1.49 V .

[ 3 ]

Question (i)

(i)

Define the term standard electrode potential.

[ 1 ]

Question (ii)

(ii)

Referring to Table 14 of the Data Booklet, deduce, giving a reason, whether the oxidation of the chromium(III) ion to the dichromate(VI) ion by the chlorate(V) ion is energetically feasible.

[ 2 ]
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