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IB Chemistry SL 3.2 Electron Transfer Reactions Questions

Practise IB Chemistry SL 3.2 with questions on oxidation states, redox equations, electrochemical cells, electrolysis and organic redox products.

Syllabus
First assessment 2025
Course
Chemistry SL
Level
SL

Exam points

  • Assign oxidation states, identify oxidized and reduced species, and balance redox half-equations in acidic or neutral solution.
  • Use electrode roles, salt bridges and electron flow to explain voltaic, rechargeable and electrolytic cells.
  • Deduce organic oxidation, reduction and hydrogenation products from functional-group changes.

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 compounds

Learn this topic

Study 3.2 Electron transfer reactions conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

Question 1

[Maximum number: 1]

Chlorine undergoes many reactions.

2.67 g of manganese(IV) oxide was added to 200.0 cm3200.0 \mathrm{~cm}^{3} of 2.00moldmm−3HCl2.00 \mathrm{moldm} \mathrm{m}^{-3} \mathrm{HCl}.

MnO2( s)+4HCl(aq)→Cl2( g)+2H2O(l)+MnCl2(aq)\mathrm{MnO}_{2}(\mathrm{~s})+4 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{MnCl}_{2}(\mathrm{aq})

Deduce, referring to oxidation states, whether MnO2\mathrm{MnO}_{2} is an oxidizing or reducing agent.

Question 2

[Maximum number: 4]

Question (a)

(a)

Ethanol is a primary alcohol that can be oxidized by acidified potassium dichromate(VI). Distinguish between the reaction conditions needed to produce ethanal and ethanoic acid.

Ethanal:
Ethanoic acid:

[ 2 ]

Question (b)

(b)

Deduce the half-equation for the oxidation of ethanol to ethanal.

[ 1 ]

Question (c)

(c)

Deduce the overall redox equation for the reaction of ethanol to ethanal with acidified potassium dichromate(VI) by combining your answer to part (c) (iii) with the following half-equation:

Cr2O72−(aq)+14H+(aq)+6e−→2Cr3+(aq)+7H2O(l)\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})+14 \mathrm{H}^{+}(\mathrm{aq})+6 \mathrm{e}^{-} \rightarrow 2 \mathrm{Cr}^{3+}(\mathrm{aq})+7 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})
[ 1 ]

Question 3

[Maximum number: 7]

Question (a)

(a)

Consider the following spontaneous reactions.

Fe( s)+Ni2+(aq)→Fe2+(aq)+Ni( s)Zn( s)+Fe2+(aq)→Zn2+(aq)+Fe( s)Ni( s)+Pb2+(aq)→Ni2+(aq)+Pb( s)\begin{aligned} & \mathrm{Fe}(\mathrm{~s})+\mathrm{Ni}^{2+}(\mathrm{aq}) \rightarrow \mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{Ni}(\mathrm{~s}) \\ & \mathrm{Zn}(\mathrm{~s})+\mathrm{Fe}^{2+}(\mathrm{aq}) \rightarrow \mathrm{Zn}^{2+}(\mathrm{aq})+\mathrm{Fe}(\mathrm{~s}) \\ & \mathrm{Ni}(\mathrm{~s})+\mathrm{Pb}^{2+}(\mathrm{aq}) \rightarrow \mathrm{Ni}^{2+}(\mathrm{aq})+\mathrm{Pb}(\mathrm{~s}) \end{aligned}
[ 3 ]

Question (i)

(i)

Deduce the order of increasing reactivity of the metals based on the reactions above.

[ 2 ]

Question (ii)

(ii)

Identify the strongest oxidizing agent in the reactions above.

[ 1 ]

Question (b)

(b)

Draw a diagram of an electrolytic cell for the electrolysis of molten nickel(II) bromide, NiBr2(l)\mathrm{NiBr}_{2}(\mathrm{l}). Include the direction of the electron flow, the polarity of electrodes and the half-equations at each electrode.

Negative electrode (cathode):

Positive electrode (anode):

[ 4 ]
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