DP Chemistry (last assessment 2024)

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Question 21M.2.hl.TZ1.5

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Date May 2021 Marks available [Maximum mark: 16] Reference code 21M.2.hl.TZ1.5
Level hl Paper 2 Time zone TZ1
Command term Deduce, Explain, Identify, Justify, Sketch, State, Suggest Question number 5 Adapted from N/A
5.
[Maximum mark: 16]
21M.2.hl.TZ1.5

Ethanol is obtained by the hydration of ethene, C2H4.

(a(i))

State the class of compound to which ethene belongs.

[1]

Markscheme

alkene ✔

(a(ii))

State the molecular formula of the next member of the homologous series to which ethene belongs.

[1]

Markscheme

C3H6 ✔

Accept structural formula.

(b(i))

Justify why ethene has only a single signal in its 1H NMR spectrum.

[1]

Markscheme

hydrogen atoms/protons in same chemical environment ✔

Accept “all H atoms/protons are equivalent”.
Accept “symmetrical”

(b(ii))

Deduce the chemical shift of this signal. Use section 27 of the data booklet.

[1]

Markscheme

4.5 to 6.0 «ppm» ✔

Accept a single value within this range.

(c)

Suggest two possible products of the incomplete combustion of ethene that would not be formed by complete combustion.

[1]

Markscheme

carbon monoxide/CO AND carbon/C/soot ✔

(d)

A white solid was formed when ethene was subjected to high pressure.

Deduce the type of reaction that occurred.

[1]

Markscheme

«addition» polymerization ✔

Ethanol is obtained by the hydration of ethene, C2H4.

Alternative synthetic routes exist to produce alcohols.

(e(i))

Sketch the mechanism for the reaction of propene with hydrogen bromide using curly arrows.

[3]

Markscheme

curly arrow going from C=C to H of HBr AND curly arrow showing Br leaving ✔

representation of carbocation ✔

curly arrow going from lone pair/negative charge on Br− to C+ ✔


Award [2 max] for mechanism producing 1-brompropane.

(e(ii))

Explain why the major organic product is 2-bromopropane and not 1-bromopropane.

[2]

Markscheme

«2-bromopropane involves» formation of more stable «secondary» carbocation/carbonium ion/intermediate
OR
1-bromopropane involves formation of less stable «primary» carbocation/carbonium ion/intermediate ✔

«increased» positive inductive/electron-releasing effect of extra–R group/–CH3/methyl «increases stability of secondary carbocation» ✔


Award [1] for “more stable due to positive inductive effect”.
Do not award marks for quoting Markovnikov’s rule without any explanation.

(e(ii))

Explain why the major organic product is 2-bromopropane and not 1-bromopropane.

[2]

Markscheme

«2-bromopropane involves» formation of more stable «secondary» carbocation/carbonium ion/intermediate
OR
1-bromopropane involves formation of less stable «primary» carbocation/carbonium ion/intermediate ✔

«increased» positive inductive/electron-releasing effect of extra–R group/–CH3/methyl «increases stability of secondary carbocation» ✔

Award [1] for “more stable due to positive inductive effect”.

Do not award marks for quoting Markovnikov’s rule without any explanation. 

(e(iii))

2-bromopropane can be converted directly to propan-2-ol. Identify the reagent required.

[1]

Markscheme

sodium hydroxide/NaOH/potassium hydroxide/KOH ✔

Accept «aqueous» hydroxide ions/OH−

(e(iv))

Propan-2-ol can also be formed in one step from a compound containing a carbonyl group.

State the name of this compound and the type of reaction that occurs.

[2]

Markscheme

Name of carbonyl compound:
propanone ✔

Type of reaction:
reduction ✔


Accept other valid alternatives, such as “2-propyl ethanoate” for M1 and “hydrolysis” for M2.

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