May/June 2026 Paper 21

2026 · 5 questions · 38 parts · 60 marks

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Context for 4(a)
Compound Z is oxidised to produce organic compound W, CHO, by heating under reflux with an excess of acidified CrO(aq).
Figure 4.1, the skeletal structural formula of compound Z, labelled Z: a central carbon bonded directly to an OH group (drawn straight up, no carbon in between), to a -CH2-OH group (HO, to the upper left), to a longer -CH2-CH2-OH group with an extra carbon (OH, to the upper right), and to a -CH2-OH group (OH, below); consistent with molecular formula C5H12O4
4(a)(i)AlcoholsEasy1 mark
Describe the colour change in this reaction.
Colour of the mixture at the start, then after, the reaction
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4(a)(ii)Oxidation Reduction Redox EquationsEasy1 mark
The complete oxidation of 0.025 mol of Z requires 0.050 mol of CrO(aq). W is produced in this reaction. Balance the equation for this reaction.
Coefficients in order: Z, CrO, H, W, Cr, HO
Context for 4(b)
Compound A is a structural isomer of Z.
Figure 4.2, the skeletal structural formula of compound A, labelled A, a structural isomer of Z: two adjacent backbone carbons, each bearing its own OH directly (HO to the upper left on the upper backbone carbon, HO to the left on the lower backbone carbon); the upper backbone carbon also carries a longer -CH2-CH2-OH arm (OH to the upper right), and the lower backbone carbon also carries a -CH2-OH arm (OH to the lower right) - overall the chain HOCH2-CH(OH)-CH(OH)-CH2-CH2OH, consistent with molecular formula C5H12O4
4(b)(i)Organic Functional Group TestsEasy2 marks
Complete Table 4.1 to show what is observed when separate samples of A are added to each reagent. State 'none' if no reaction occurs.
reagentobservation with A
Na(s)
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2,4-dinitrophenylhydrazine (2,4-DNPH)
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Fehling's reagentnone
4(b)(ii)Organic Functional Group TestsEasy1 mark
Suggest why Fehling's reagent does not react with A but does react with aldehyde functional groups.

Answer

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4(b)(iii)AlcoholsMedium2 marks
Compound A is heated under reflux with an excess of acidified CrO(aq) to produce organic compound Y. Draw the structure of Y.
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4(c)Aldehydes KetonesMedium2 marks
Compound B reacts with an excess of LiAlH to produce organic compound C. Complete the equation in Figure 4.3 to show the reaction of B with an excess of LiAlH to produce C. [H] represents one atom of hydrogen from the reducing agent, LiAlH.
Diagram to annotate
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