DP Chemistry (last assessment 2024)

Test builder »

Question 21N.2.hl.TZ0.10

Select a Test
Date November 2021 Marks available [Maximum mark: 17] Reference code 21N.2.hl.TZ0.10
Level hl Paper 2 Time zone TZ0
Command term Apply, Deduce, Determine, Discuss, Distinguish, Explain, Identify, Justify, State Question number 10 Adapted from N/A
10.
[Maximum mark: 17]
21N.2.hl.TZ0.10

Hybridization of hydrocarbons affects their reactivity.

(a(i))

Distinguish between a sigma and pi bond.

[2]

Markscheme

Sigma (σ) bond:

overlap «of atomic orbitals» along the axial / intermolecular axis / electron density is between nuclei
OR
head-on/end-to-end overlap «of atomic orbitals» ✔

 

Pi (π) bond:

overlap «of p-orbitals» above and below the internuclear axis/electron density above and below internuclear axis
OR
sideways overlap «of p-orbitals» ✔

 

Accept a suitable diagram.

(a(ii))

Identify the hybridization of carbon in ethane, ethene and ethyne.

[1]

Markscheme


All 3 required for mark.

(b(i))

State, giving a reason, if but-1-ene exhibits cis-trans isomerism.

[1]

Markscheme

no AND 2 groups on a carbon «in the double bond» are the same/hydrogen «atoms»

OR

no AND molecule produced by rearranging atoms bonded on a carbon «in the double bond» is the same as the original ✔

(b(ii))

State the type of reaction which occurs between but-1-ene and hydrogen iodide at room temperature.

[1]

Markscheme

«electrophilic» addition ✔

 

Do not allow nucleophilic addition.

(b(iii))

Explain the mechanism of the reaction between but-1-ene with hydrogen iodide, using curly arrows to represent the movement of electron pairs.

[4]

Markscheme

curly arrow going from C=C to H of HI AND curly arrow showing I leaving ✔

representation of carbocation ✔

curly arrow going from lone pair/negative charge on I– to C+ ✔

2-iodobutane formed ✔

 

Penalize incorrect bond, e.g. –CH–H3C or –CH3C once only.

(b(iv))

State, giving a reason, if the product of this reaction exhibits stereoisomerism.

[1]

Markscheme

yes AND has a carbon attached to four different groups
OR
yes AND it contains a chiral carbon ✔


Accept yes AND mirror image of molecule different to original/non-superimposable on original.

Experiments were carried out to investigate the mechanism of reaction between 2-chloropentane and aqueous sodium hydroxide.

(c(i))

Deduce the rate expression for this reaction.

[1]

Markscheme

«rate =» k[NaOH][C5H11Cl] ✔

(c(ii))

Deduce the units of the rate constant.

[1]

Markscheme

mol–1 dm3 s–1 ✔

(c(iii))

Determine the initial rate of reaction in experiment 4.

[2]

Markscheme

ALTERNATIVE 1:

«k = » 1.25 «mol–1 dm3 s–1» ✔

 

«rate = 1.25 mol–1 dm3 s–1 × 0.60 mol dm–3 × 0.25 mol dm–3»

1.9 x 10–1 «mol dm–3 s–1» ✔

 

ALTERNATIVE 2:

«[NaOH] exp. 4 is 3 × exp. 1»

«[C5H11Cl] exp. 4 is 2.5 × exp. 1»

«exp. 4 will be » 7.5× faster ✔

1.9 x 10–1 «mol dm–3 s–1» ✔

 

Award [2] for correct final answer.

(d)

Deduce, with a reason, the mechanism of the reaction between 2-chloropentane and sodium hydroxide.

[1]

Markscheme

SN2 AND rate depends on both OH– and 2-chloropentane ✔


Accept E2 AND rate depends on both OH– and 2-chloropentane.

(e)

Discuss the reason benzene is more reactive with an electrophile than a nucleophile.

[2]

Markscheme

delocalized electrons/pi bonds «around the ring»
OR
molecule has a region of high electron density/negative charge ✔

electrophiles are attracted/positively charged AND nucleophiles repelled/negatively charged ✔

 

Do not accept just “nucleophiles less attracted” for M2.

Accept “benzene AND nucleophiles are both electron rich” for “repels nucleophiles”.

Syllabus sections