DP Chemistry (first assessment 2025)

Question SPM.2.SL.TZ0.4

Date	May Specimen-2023	Marks available	[Maximum mark: 16]	Reference code	SPM.2.SL.TZ0.4
Level	SL	Paper	2	Time zone	TZ0
Command term	Calculate, Determine, Discuss, Explain, Identify, Outline, State, Write	Question number	4	Adapted from	N/A

[Maximum mark: 16]

SPM.2.SL.TZ0.4

Heptadecane, C₁₇H₃₆, can be extracted from crude oil or cactus plants.

(a)

Write an equation for the complete combustion of C₁₇H₃₆.

[1]

Markscheme

C₁₇H₃₆(l) + 26O₂(g) → 17CO₂(g) + 18H₂O(l) ✔

(b)

The enthalpy of combustion of C₁₇H₃₆ is −11 350 kJ mol⁻¹.

(b.i)

Calculate the maximum energy produced when 2.00 g of C₁₇H₃₆ is combusted.

[2]

Markscheme

nC₁₇H₃₆ = « $\frac{2.00 g}{[(17 \times 12.01 g {mol}^{- 1}) + (36 \times 1.01 g {mol}^{- 1})]} = \frac{2.00 g}{240.53 g {mol}^{- 1}} = »$

0.008315/0.00831 «mol» ✔
« energy = 11350 kJ mol^{$-$ 1} × 0.008315 mol = » 94.4 «kJ» ✔

(b.ii)

Determine the maximum temperature change when 500.0 cm³ of water is heated by a 2.00 g sample of C₁₇H₃₆.

[2]

Markscheme

94 400 = 500.0 × 4.18 × $Δ$ T ✔
$Δ$ T = 45.2«K» ✔

(b.iii)

Outline two assumptions made in the calculation in (b)(ii).

[2]

Markscheme

Any two:
water does not evaporate  ✔
heat is not lost to the surroundings
OR
all heat is transferred to the water  ✔
density of water is 1 g cm^{$-$ 3}  ✔
water is pure  ✔
complete combustion  ✔

(c)

Explain why biofuels contribute less to climate change than fossil fuels.

[1]

Markscheme

CO₂ consumed while plant is growing «and later released when biofuel is combusted»
OR
photosynthesis uses up CO₂ «later released when biofuel is combusted» ✔

(d)

Heptadecane can be broken down into smaller molecules. Consider the reaction:

C₁₇H₃₆(g) → 2 C₂H₄(g) + C₁₃H₂₈(g)

Determine the standard enthalpy change, $Δ$ H^⦵, for the reaction stated, using section 12 of the data booklet.

[3]

Markscheme

bonds broken: 4(C $-$ C) / 4 × 346  ✔
bonds formed: 2(C=C) / 2 × 614  ✔
$Δ$ H^⦵ = «4 × 346 $-$ 2 × 614 / 1384 $-$ 1228 =»
«+»156 «kJ»  ✔

Award [3] for correct final answer.

(e)

Ethene can be converted to ethanol in one reaction. State the equation for this reaction.

[1]

Markscheme

C₂H₄ (g) + H₂O (g) → C₂H₅OH (g) ✔

(f)

Ethanol reacts with oleic acid to produce ethyl oleate.

C₁₇H₃₃COOH (l) + CH₃CH₂OH (l) $⇌$ C₁₇H₃₃COOCH₂CH₃ (l) + X (l)

(f.i)

Identify the side product X (l).

[1]

Markscheme

H₂O / water ✔

(f.ii)

Calculate the atom economy of the reaction.

[1]

Markscheme

«20(12.01) + 38(1.01) + 2(16.00) = 310.58

$\frac{100 \times 310.58}{(310.58 + 18.02)}$ = »

94.5 % ✔

(f.iii)

Discuss why the atom economy of a reaction is an important consideration when evaluating the impact of a reaction in an industrial process.

[2]

Markscheme

Any two of:
sustainable development  ✔
more economical/efficient  ✔
better use of natural resources  ✔
reduces waste  ✔

Question SPM.2.SL.TZ0.4

Select a Test

Confirm action