DP Chemistry (first assessment 2025)

Question 23M.2.HL.TZ1.6

Date	May 2023	Marks available	[Maximum mark: 11]	Reference code	23M.2.HL.TZ1.6
Level	HL	Paper	2	Time zone	TZ1
Command term	Calculate, Determine, Explain, Formulate, Suggest	Question number	6	Adapted from	N/A

[Maximum mark: 11]

23M.2.HL.TZ1.6

The element sulfur has many industrial uses.

(a.i)

Determine the standard enthalpy of reaction ( $Δ H_{r}^{⦵}$ ), in kJ mol⁻¹, for the oxidation of SO₂ to SO₃.

Substance	Enthalpy of formation, ( $Δ H_{f}^{⦵}$ ), in kJ mol⁻¹
SO₂	−296.8
SO₃	−395.8

[1]

Markscheme

«ΔH°rxn = ΣΔH°f (Products) − ΣΔH°f (Reactants) =»
−395.8 − (−296.8)» = −99.0«kJ mol⁻¹» ✓

(a.ii)

Formulate equations showing how SO₂ and SO₃ lead to acid deposition.

SO₂: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SO₃: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[1]

Markscheme

SO₂_(aq) + H₂O(l) ⇌ H₂SO₃ _(aq)
AND
SO₃ _(aq) + H₂O (l) → H₂SO₄ _(aq) ✓

Accept single arrow for the first equation.

(a.iii)

Explain the polarity of the S—O bond. Use section 8 of the data booklet.

[2]

Markscheme

significant/large/0.8 difference in electronegativity/oxygen more electronegative ✓
oxygen «dipole partially» negative/sulfur «dipole partially» positive
OR
oxygen more negative/higher electron density «around it than sulfur» ✓

Accept suitable diagram showing the O—S dipole.

(b)

The combustion of 0.1 moles of sulfur (S) was demonstrated in a school laboratory using the following apparatus in a fume cupboard.

(b.i)

Calculate the enthalpy of combustion of sulfur, ΔH_c, in kJ mol⁻¹ from this data. Use sections 1 and 2 of the data booklet.

Mass of water (g) ±0.01	50.00
Initial temperature of water (°C) ±0.5	20.0
Final temperature of water (°C) ±0.5	35.0

[2]

Markscheme

«q = −mcΔT = 50.00 g × 4.18 J K⁻¹ g⁻¹ × (35.0-20.0) °C =» −3140.0 «J» ✓
«(3140/0.1)/1000 =» −31.4 «kJ mol⁻¹» ✓

Award [1 max] for +31.4 kJ mol⁻¹
Award [2] for correct final answer.

(b.ii)

Suggest the major source of systematic error in this experiment and an improvement to reduce this error.

Source of systematic error: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

Improvement: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

[2]

Markscheme

Source of systematic error:
heat loss «to the surroundings» ✓

Improvement:
insulate reaction apparatus/put a lid on the beaker
OR
use a bomb/calibrated calorimeter
OR
use of windbreak around the dish/apparatus ✓

(b.iii)

Calculate the percentage uncertainty in the temperature change to two significant figures.

[1]

Markscheme

«1.0/15.0 x 100 =» 6.7«%» ✓

$\sqrt{\frac{0 . 5^{2} + 0 . 5^{2}}{15.0}} \times 100 % \approx 5 %$

Do not allow 6.6%

Accept "5%" if the formula $\sqrt{\sum {(∆ A)}^{2}}$ is used.

(b.iv)

Suggest one way of reducing the percentage uncertainty in this experiment.

[1]

Markscheme

more precise/more divisions per degree «on the thermometer»
OR
more precise balance
OR
larger quantities of sulfur/water
OR
larger temperature change ✓

Do not accept more repetitions.

(b.v)

Calculate the overall percentage error of this experiment. Use part (b)(i) and section 13 of the data booklet. (If you did not obtain an answer for part (b)(i) use −50.0 kJ mol⁻¹, but this is not the correct value.)

[1]

Markscheme

« −297 kJ mol⁻¹ − −31.4 kJ mol⁻¹/−297 kJ mol⁻¹ × 100 =» 89.4 «%» ✓

alternate:
« −297 kJ mol⁻¹ − −50.0 kJ mol⁻¹/−297 kJ mol⁻¹ × 100 =» 83.2 «%» ✓

Question 23M.2.HL.TZ1.6

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