DP Chemistry (first assessment 2025)

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Question 23M.2.HL.TZ2.6

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Date May 2023 Marks available [Maximum mark: 14] Reference code 23M.2.HL.TZ2.6
Level HL Paper 2 Time zone TZ2
Command term Determine, Draw, Explain, Predict, State, Suggest, Write Question number 6 Adapted from N/A
6.
[Maximum mark: 14]
23M.2.HL.TZ2.6

Bromine, Br2 (l), and methanoic acid, HCOOH (aq), react in the presence of sulfuric acid.

Br2 (l) + HCOOH (aq) → 2HBr (aq) + CO2 (g)

(a)

Suggest an experimental method that could be used to determine the rate of reaction.

[2]

Markscheme

«measure change in»
mass
OR
pressure
OR
volume of gas/CO2 produced
OR
«intensity of» colour
OR
«electrical» conductivity
OR
pH ✓

with time ✓

 

Accept any of the following for M1:
perform experiment on balance
OR
use pressure probe
OR
collect gas/gas syringe
OR
use colorimeter
OR
use conductivity meter
OR
use pH meter

Do not accept “measure rate of change” for M2.

(b)

The sulfuric acid is a catalyst in this reaction. Explain how a catalyst increases the reaction rate.

[2]

Markscheme

provides an alternative reaction pathway AND lower activation energy/Ea ✓
larger fraction/number of molecules with E ≥ Ea/enough energy «for a successful collision» ✓

(c)

Methanoic acid can react with ethanol to produce an ester.

(c.i)

Draw the full structural formula of the organic product and state its name.

Structural formula:

 

 

 

 

 

 

 

Name: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[2]

Markscheme

Structural formula:

Name:
ethyl methanoate ✓

(c.ii)

Predict the number of signals, and their splitting patterns, in the 1H NMR spectrum of this organic product.

 

Number of signals: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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

Splitting patterns: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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

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

[2]

Markscheme

Number of signals:
3 ✓

Splitting patterns:
singlet/1
AND
quartet/4
AND
triplet/3 ✓

(c.iii)

State one reason why tetramethylsilane, TMS, is often chosen as an internal reference standard for the calibration of 1H NMR spectroscopy.

[2]

Markscheme

Any two of the following:
chemical shift/signal outside range of common chemical shift/signal ✓
strong signal/12/all H atoms in same environment ✓
singlet/no splitting of signal ✓
volatile/easily separated/easily removed ✓
inert/stable ✓
soluble in most organic solvents ✓

 

Do not accept chemical shift = 0.

(d.i)

Write the equation for the complete combustion of ethanol.

[1]

Markscheme

CH3CH2OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g) ✓

 

Accept C2H6O for ethanol.

(d.ii)

Determine the enthalpy change for the combustion of ethanol, in kJ mol−1, using section 11 of the data booklet.

[3]

Markscheme

«bond breaking»
1 C−C + 5 C−H + 1 C−O + 1 O−H + 3 O=O / 346 + 5(414) + 358 + 463 +3(498) / 4731 «kJ» ✓

«bond forming»
4 C=O + 6 O−H / 4(804) + 6(463) / 5994 «kJ» ✓

ΔH «= 4731−5994» = −1263 «kJ mol−1» ✓

 

Award [3] for correct final answer.