49 exam-style questions on Electron transfer reactions (redox) — topic R3.2 of Reactivity 3: What are the mechanisms of chemical change? in the IB Chemistry syllabus — with answers and explanations. Samples below; the full set is free with an account.
When a primary alcohol is oxidised by acidified potassium dichromate under reflux, what is the final organic product?
Answer: A carboxylic acid
A primary alcohol is oxidised first to an aldehyde, then further to a carboxylic acid. Under reflux (which keeps the aldehyde in the flask), oxidation goes all the way to the carboxylic acid. Distilling would allow the aldehyde to be collected instead. The orange dichromate turns green (Cr3+).
What is the oxidation number of sulfur in the sulfate ion, SO₄²⁻?
Answer: +6
Each oxygen is −2, giving −8 total. For the overall charge of −2: S + (−8) = −2, so S = +6.
In an electrochemical cell, at which electrode does oxidation always take place?
Answer: the anode
Oxidation occurs at the anode and reduction at the cathode in both voltaic and electrolytic cells (remember: AN-OX and RED-CAT).
Determine the oxidation state of chromium in the dichromate ion, Cr₂O₇²⁻.
Answer: +6
Oxygen is −2: 7(−2) = −14; overall charge −2, so 2Cr = +12, each Cr = +6.
In the reaction Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), identify the reducing agent.
Answer: Zn(s)
Zn is oxidised (loses electrons) and so is the reducing agent; it reduces Cu²⁺ to Cu.
Using the reactivity series, determine which metal will displace copper from aqueous copper(II) sulfate but NOT displace magnesium from magnesium sulfate.
Answer: Iron
Iron is more reactive than copper (so displaces Cu) but less reactive than magnesium (so cannot displace Mg).
That was 6 of 49 Electron transfer reactions (redox) questions.
Practise all 49 freeDetermineAO2 · 1–4 marks
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StateAO1 · 1–2 marks
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49 Electron transfer reactions (redox) questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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