A-LevelChemistryGroup 179701/21 · Oct/Nov 2020 · Q416 Marks

Iodine is used in many inorganic and organic reactions.

(a)(i)State and explain the trend in volatility of the halogens, from chlorine to iodine.[2]
(a)(ii)Explain why HI is the least thermally stable of HCl, HBr and HI.[1]
(a)(iii)The table shows the electronegativity values for hydrogen, fluorine and iodine. element | electronegativity value ---|--- H | 2.1 F | 4.0 I | 2.5 Explain, in terms of intermolecular forces, why HI has a lower boiling point than HF.[2]
(a)(iv)Iodine reacts with hot concentrated aqueous sodium hydroxide in the same way as chlorine. Write an equation for the reaction of iodine and hot aqueous sodium hydroxide.[1]
(b)(i)Iodoalkanes contain carbon-iodine bonds. The simplest iodoalkane is CH3I. CH3I can be made from methanol, CH3OH. Identify a reagent that can convert CH3OH to CH3I.[1]
(b)(ii)1,2-diiodoethane, CH₂ICH2I, can be made by bubbling ethene into liquid iodine. Fully name the type of mechanism shown in this reaction.[1]
(c)(i)J reacts with NaOH, forming different products dependent on the conditions used. [Figure 4.1: Structure of J (2-iodo-2-methylbutane)] Name J.[1]
(c)(ii)J reacts with NaOH(aq) to form K. [Figure 4.2: Structure of K (2-methylbutan-2-ol)] Fully name the mechanism of the reaction of J with NaOH(aq) to form K.[1]
(c)(iii)J reacts with NaOH dissolved in ethanol to form a mixture of two alkenes, L and M. Alkene L is shown. [Figure 4.3: Structure of L (2-methylbut-1-ene)] In the box provided, draw the structure of M.[1]
(c)(iv)Explain why L does not show geometrical (cis-trans) isomerism.[1]
(c)(v)L reacts with hot concentrated acidified KMnO4(aq) to form propanone and one other organic product. Identify the other organic product.[1]
(c)(vi)Propanone reacts with excess alkaline aqueous iodine. Complete and balance the equation for this reaction. CH3COCH3 + .....I₂ + .....OH⁻ → .....CH3COO⁻ + .....H₂O + .....I⁻ + .....[2]
(c)(vii)State one observation that can be made in the reaction in (c)(vi).[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] M1: (Volatility) decreases (down the group)
[1] M2: more electrons so greater intermolecular forces / intermolecular attractions OR more electrons so greater VdW between molecules
[1] (HI has the) lowest bond enthalpy
[1] M1: HF has permanent dipole(-dipole forces) AND HI has ((only)) instantaneous dipole / induced dipole (forces) / permanent dipole(-dipole forces)
[1] M2: IMF's in HI are weaker (than IMF's in HF)
[1] 3I2 + 6NaOH → 5NaI + NaIO3 + 3H2O
[1] HI(g) / PI3 / P and I2
[1] Electrophilic addition
[1] 2-iodo-2-methylbutane
[1] Nucleophilic substitution / SN
[1] Structure of M is 2-methylbut-2-ene (CH3C(CH3)=CHCH3)
[1] (L has) two identical / two methyl groups attached to one end / one carbon of the C=C / double bond
[1] ethanoic acid / CH3COOH
[1] M1: correctly balanced
[1] M2: CHI3 product
[1] yellow ppt / yellow solid