FRQ — d- and f-Block Elements

Case study·Standard multi-step (3/5)·No calculator

Difficulty guide

The label describes the problem, not your ability.

1/5 - Foundational

Warm-up setup; checks one basic idea.

2/5 - Routine exam skill

Normal syllabus skill; usually one main rule or interpretation.

3/5 - Standard multi-step

Exam-style problem with multiple steps or a common trap.

4/5 - Hard exam skill

High-end exam problem; combines methods carefully.

5/5 - Challenge

Stretch problem beyond normal exam pressure.

Question

A student has two oxidising reagents: acidified

\mathrm{K_2Cr_2O_7}

and acidified

\mathrm{KMnO_4}

. The student must oxidise

\mathrm{Fe^{2+}}

in separate tests and compare the mole ratios of oxidant to

\mathrm{Fe^{2+}}

Total: 3 marks

(a) How many moles of $\mathrm{Fe^{2+}}$ are oxidised by $1$ mole of $\mathrm{Cr_2O_7^{2-}}$ in acid? (1 mark)

(b) How many moles of $\mathrm{Fe^{2+}}$ are oxidised by $1$ mole of $\mathrm{MnO_4^-}$ in acid? (1 mark)

Your response (optional — you can also work on paper)

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