DP Chemistry (first assessment 2025)

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Question 22M.2.HL.TZ1.5

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Date May 2022 Marks available [Maximum mark: 17] Reference code 22M.2.HL.TZ1.5
Level HL Paper 2 Time zone TZ1
Command term Apply, Deduce, Draw, Explain, Identify, Justify, Outline, State Question number 5 Adapted from N/A
5.
[Maximum mark: 17]
22M.2.HL.TZ1.5

Organomagnesium compounds can react with carbonyl compounds. One overall equation is:

Compound B can also be prepared by reacting an alkene with water.

Iodomethane is used to prepare CH3MgI. It can also be converted into methanol:

CH3I + HO → CH3OH + I

(a(i))

State the name of Compound B, applying International Union of Pure and Applied Chemistry (IUPAC) rules.

[1]

Markscheme

2-methylpropan-2-ol /2-methyl-2-propanol ✔

 

Accept methylpropan-2-ol/ methyl-2-propanol.

Do not accept 2-methylpropanol.

Examiners report

Naming the organic compound using IUPAC rules was generally done well.

(a(ii))

Compound A and Compound B are both liquids at room temperature and pressure. Identify the strongest intermolecular force between molecules of Compound A.

[1]

Markscheme

dipole-dipole ✔

 

Do not accept van der Waals’ forces.

(a(iii))

State the number of σ (sigma) and π (pi) bonds in Compound A.

[1]

Markscheme

σ: 9
AND
π: 1 ✔

Examiners report

Mediocre performance in stating the number of σ (sigma) and π (pi) bonds in propanone; the common answer was 3 σ and 1 π instead of 9 σ and 1 π, suggesting the three C-H σ bonds in each of the two methyl groups were ignored.

(a(iv))

Deduce the hybridization of the central carbon atom in Compound A.

[1]

Markscheme

sp2

Examiners report

sp2 hybridization of the central carbon atom in the ketone was very done well.

(a(v))

Identify the isomer of Compound B that exists as optical isomers (enantiomers).

[1]

Markscheme

butan-2-ol/CH3CH(OH)C2H5

Examiners report

Mediocre performance; some identified 2-methylpropan-1-ol or -2-ol, instead butan-2-ol/CH3CH(OH)C2H5 as the isomer that exists as an optical isomer.

(b(i))

Draw the structural formula of the alkene required.

[1]

Markscheme

Examiners report

Good performance; some had a H and CH3 group on each C atom across double bond instead of having two H atoms on one C and two CH3 groups on the other.

(b(ii))

Explain why the reaction produces more (CH3)3COH than (CH3)2CHCH2OH.

[2]

Markscheme

carbocation formed from (CH3)3COH is more stable / (CH3)3C+ is more stable than (CH3)2CHCH2+


«because carbocation has» greater number of alkyl groups/lower charge on the atom/higher e- density
OR
«greater number of alkyl groups» are more electron releasing
OR
«greater number of alkyl groups creates» greater inductive/+I effect ✔

 

Do not award any marks for simply quoting Markovnikov’s rule.

Examiners report

Poor performance, particularly in light of past feedback provided in similar questions since there was repeated reference simply to Markovnikov's rule, without any explanation.

(b(iii))

Deduce the structural formula of the repeating unit of the polymer formed from this alkene.

[1]

Markscheme

Do not penalize missing brackets or n.

Do not award mark if continuation bonds are not shown.

Examiners report

Mediocre performance; deducing structural formula of repeating unit of the polymer was challenging in which continuation bonds were sometimes missing, or structure included a double bond or one of the CH3 group was missing.

(c)

Deduce what would be observed when Compound B is warmed with acidified aqueous potassium dichromate (VI).

[1]

Markscheme

no change «in colour/appearance/solution» ✔

Examiners report

Mediocre performance; deducing whether the tertiary alcohol could be oxidized solicited mixed responses ranging from the correct one, namely no change (in colour, appearance or solution), to tertiary alcohol will be reduced, or oxidized, or colour will change will occur, and such.

(d(i))

Identify the type of reaction.

[1]

Markscheme

«nucleophilic» substitution
OR
SN2 ✔


Accept “hydrolysis”.

Accept SN1

Examiners report

Excellent performance on the type of reaction but with some incorrect answers such as alkane substitution, free radical substitution or electrophilic substitution.

(d(ii))

Outline the requirements for a collision between reactants to yield products.

[2]

Markscheme

energy/E ≥ activation energy/Ea

correct orientation «of reacting particles»
OR
correct geometry «of reacting particles» ✔

Examiners report

Good performance. For the requirements for a collision between reactants to yield products, some suggested necessary, sufficient or enough energy or even enough activation energy instead of energy/E ≥ activation energy/Ea.

(d(iii))

Explain the mechanism of the reaction using curly arrows to represent the movement of electron pairs.

[3]

Markscheme

curly arrow going from lone pair/negative charge on O in -OH to C ✔

curly arrow showing I leaving ✔

representation of transition state showing negative charge, square brackets and partial bonds ✔

 

Accept OH- with or without the lone pair.

Do not allow curly arrows originating on H, rather than the -, in OH-.

Accept curly arrows in the transition state.

Do not penalize if HO and I are not at 180°.

Do not award M3 if OH–C bond is represented.

Award [2 max] if SN1 mechanism shown.

Examiners report

Mechanism for SN2 not done well. Often the negative charge on OH was missing, the curly arrow was not going from lone pair/negative charge on O in -OH to C, or the curly arrow showing I leaving placed incorrectly and specially the negative charge was missing in the transition state. Formation of a carbocation intermediate indicating SN1 mechanism could score a maximum of 2 marks.

(d(iv))

The polarity of the carbon–halogen bond, C–X, facilitates attack by HO.

Outline, giving a reason, how the bond polarity changes going down group 17.

[1]

Markscheme

decreases/less polar AND electronegativity «of the halogen» decreases ✔

 

Accept “decreases” AND a correct comparison of the electronegativity of two halogens.

Accept “decreases” AND “attraction for valence electrons decreases”.

Examiners report

Good performance on how the polarity of C-X bond changes going down group 17.

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