DP Chemistry (first assessment 2025)

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Question 23M.2.HL.TZ1.3

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Date May 2023 Marks available [Maximum mark: 13] Reference code 23M.2.HL.TZ1.3
Level HL Paper 2 Time zone TZ1
Command term Draw, Identify, Outline, Sketch, State Question number 3 Adapted from N/A
3.
[Maximum mark: 13]
23M.2.HL.TZ1.3

Alkanes form a homologous series.

(a.i)

Outline the meaning of homologous series.

[1]

Markscheme

compounds of the same family AND general formula
OR
compounds of the same family AND differ by a common structural unit/CH2 ✓

 

Accept contains the same functional group for same family.

(a.ii)

State the preferred IUPAC name for the following compounds.

[2]

Markscheme

  2-chlorobutane ✓

 1-chloro-2-methylpropane ✓

 

Accept 1-chloromethylpropane for M2, but not 2-methyl-1-chloropropane.

(a.iii)

Identify one chiral carbon atom present in one of the following structures with an asterisk (*).

[1]

Markscheme

 ✓

(a.iv)

But-2-ene can be polymerized. Draw a section of the resulting polymer showing two repeating units.

[1]

Markscheme

 ✓

 

Allow any orientation of methyl groups.
Ignore square brackets and “n”.
Continuation lines must be shown.

(b)

Chloroethane can be converted into ethanoic acid in a two-step process.

Identify reagents for each step.

 

Step 1: .............................................................................................................................................

........................................................................................................................................................


Step 2: .............................................................................................................................................

........................................................................................................................................................

 

[2]

Markscheme

Step 1:
KOH(aq)/NaOH(aq)/OH−1(aq) ✓

Step 2:
KMnO4
OR
acidified/H+ AND K2Cr2O7 ✓

 

Do not accept H2O for KOH(aq)/NaOH(aq)/OH−1(aq) for M1.
Accept potassium permanganate/MnO4−/dichromate/Cr2O72− for M2.
Accept H2SO4 as acid.
Do not allow any other acid.

(c.i)

Identify the type of reaction that takes place in step 1 of part (b).

[1]

Markscheme

Nucleophilic AND substitution. ✓
 

Allow SN2.
Do not allow SN1.
Do not allow hydrolysis.

(c.ii)

Sketch the mechanism of the reaction for step 1 in part (b), using curly arrows to show the movement of electron pairs.

[4]

Markscheme

curly arrow going from lone pair/negative charge on O in −OH to C ✓
curly arrow showing Cl leaving ✓
representation of transition state showing negative charge, square brackets and partial bonds ✓
correct products ✓

 

Accept OH− with or without the lone pair.
Do not allow curly arrows originating on H in OH−.
Accept curly arrows in the transition state.
Do not penalize if HO and Cl are not at 180°.
Do not award M3 if OH–C bond is represented.
If the answer in 3 (c) (i) is correct Award [3 max] for SN1 mechanism.
if answer in 3 (c) (i) is SN1, award [4] for SN1 mechanism.

(c.iii)

Identify the products formed from the reaction of ethanol and ethanoic acid in the presence of an acid catalyst.

[1]

Markscheme

ethyl ethanoate/CH3CH2OOCCH3 AND water/H2O. ✓
 

Accept structural/skeletal formulae.