A student obtained the following data to calculate $q$, using $q=mc\mathrm{\Delta }T$.

$m=20.2 \mathrm{g}\pm 0.2 \mathrm{g}$

$∆T=10°\mathrm{C}\pm 1°\mathrm{C}$

$c=4.18 \mathrm{J} {\mathrm{g}}^{-1} {\mathrm{K}}^{-1}$

What is the percentage uncertainty in the calculated value of $q$?

A.  $0.2$

B.  $1.2$

C.  $11$

D.  $14$

C

Just over ½ of the candidates could propagate uncertainties from absolute to relative.

A student measured the change in mass on heating a sample of calcium carbonate, CaCO₃(s). What is the mass loss?

Mass before heating: 2.347 g ± 0.001
Mass after heating: 2.001 g ± 0.001 

A. 0.346g ± 0.001 

B. 0.346g ± 0.002 

C. 0.35g ± 0.002 

D. 0.35g ± 0.001

B

What is the Index of Hydrogen Deficiency (IHD) for 1,3,5-hexatriene (C₆H₈)?

A.     1

B.     3

C.     5

D.     6

B

What is the density, in g$$cm⁻³, of a 34.79 g sample with a volume of 12.5 cm³?

A.     0.359

B.     0.36

C.     2.783

D.     2.78

D

How should the difference between 27.0 ± 0.3 and 9.0 ± 0.2 be shown?

A.  18.0 ± 0.1

B.  18.0 ± 0.3

C.  18.0 ± 0.5

D.  18.0 ± 0.6

C

What is the graphical relationship between n and T in the ideal gas equation, pV = nRT, all other variables remaining constant?

D

Which region of the electromagnetic spectrum is used to identify hydrogen environments in a molecule?

A.  X-ray

B.  UV

C.  IR

D.  radio waves

D

Not even a quarter of candidates knew the region of the electromagnetic spectrum associated with identifying hydrogen environments. This was the lowest scoring question on the exam with the most popular answer
being IR region.

Determine the index of hydrogen deficiency (IHD) of paracetamol.

A.  3

B.  4

C.  5

D.  6

C

What is the ratio of the areas of the signals in the ¹H NMR spectrum of pentan-3-ol?

A.     6:4:1:1

B.     6:2:2:2

C.     5:5:1:1

D.     3:3:2:2:1:1

A

Which feature of a molecule does infrared spectrometry detect?

A.     molecular mass

B.     bonds present

C.     total number of protons

D.     total number of proton environments

B

What is the index of hydrogen deficiency, IHD, of 3-methylcyclohexene?

A.     0

B.     1

C.     2

D.     3

C

What is the uncertainty, in cm³, of this measurement?

A.  ±0.01

B.  ±0.1

C.  ±0.15

D.  ±1

C

This question generated a lot of debate among teachers and examiners. The answer B is the best answer but it is a rather low value. It was selected by 34% of the candidates. Many teachers argued that the correct answer should be 0.5 cm³.

Which graph shows the relationship between the pressure and volume of a sample of gas at constant temperature?

B

What can be deduced from the mass spectrum of CH₃COCH₂CH₂CH₃?

NIST Mass Spectrometry Data Center Collection (C) 2021 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved. 2-Pentanone Mass Spectrum, MS Number 291264. [graph] Available at: https://webbook.nist.gov/cgi/cbook.cgi?ID=C107879&Units=SI&Mask=200#Mass-Spec2-pentanone [Accessed 4 May 2020]. source adapted.

A.  The molar mass is 43 g mol⁻¹.

B.  The atoms have many isotopes.

C.  The most likely bond to break is C–C between carbons 2 and 3.

D.  The signal with the largest mass is due to the oxidation of the ketone in the spectrometer.

C

A student performed an experiment to find the melting point of sulfur, obtaining 118.0 °C. The literature value is 115.2 °C. What was the percentage error?

A.  $\frac{118.0-115.2}{115.2}\times 100\%$

B.  $\frac{115.2}{118.0}\times 100\%$

C.  $\frac{118.0-115.2}{118.0}\times 100\%$

D.  $\frac{118.0}{115.2}\times 100\%$

A

What is the index of hydrogen deficiency (IHD) in cyclohexanol?

A.  $0$

B.  $1$

C.  $2$

D.  $3$

B

Slightly more than half of candidates could deduce an index of hydrogen deficiency. It was a poor discriminating question with distractors being chosen equally. 

A student performs an acid-base titration using a pH meter, but forgets to calibrate it. Which type of error will occur and how will it affect the quality of the measurements?

A. Random error and lower precision

B. Systematic error and lower accuracy

C. Systematic error and lower precision

D. Random error and lower accuracy

B

What is always correct about the molecular ion, M⁺, in a mass spectrum of a compound?

A. The M⁺ ion peak has the smallest m/z ratio in the mass spectrum.

B. The m/z ratio of the M⁺ ion peak gives the relative molecular mass of the molecule.

C. The M⁺ ion is the most stable fragment formed during electron bombardment.

D. The M⁺ ion peak has the greatest intensity in the mass spectrum. 

B

What can be determined about a molecule from the number of signals in its ¹H$$NMR spectrum?

A.     Bonds present

B.     Molecular formula

C.     Molecular mass

D.     Number of hydrogen environments

D

Which graph represents the relationship between the amount of gas, n, and the absolute temperature, T, with all other variables in the ideal gas equation, PV = nRT, held constant?

B

56% of the candidates selected the correct graph representing the relationship between the amount of gas and its absolute temperature. The most commonly chosen distractor gave a directly proportional relationship.

The enthalpy of combustion of a fuel was determined using the calorimeter shown. The final result was lower than the literature value.

Which factors could have contributed to this error?

I.   Not all heat from the combustion was transferred to the calorimeter.
II.  Incomplete combustion occurred.
III. The temperature probe touched the bottom of the calorimeter.

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

A

How many signals are observed in the ¹H NMR spectrum of this compound?

A.  1

B.  2

C.  3

D.  4

A

The compound used for this ¹H NMR question was unfamiliar to the candidates and it was a skeletal formula. They were expected to notice its symmetry and that all H’s had the same chemical environment. The majority of candidates saw only part of this symmetry and decided on two chemical environments. 29% of the candidates obtained the correct answer. Some teachers commented on the difficulty of this question.

A reaction has an activation energy of 40 kJ mol⁻¹ and an enthalpy change of −60 kJ mol⁻¹.

Which potential energy diagram illustrates this reaction?

C

Very well answered. 82% of the candidates selected the potential energy diagram with the correct activation energy and enthalpy change to represent the reaction.

How are the uncertainties of two quantities combined when the quantities are multiplied together?

A.     Uncertainties are added.

B.     % uncertainties are multiplied.

C.     Uncertainties are multiplied.

D.     % uncertainties are added.

D

What is the degree of unsaturation (index of hydrogen deficiency) for the molecule?

A. 1

B. 2

C. 4

D. 5

D

IHD was the worst answered question on Paper 1, with a low discriminatory index so handled poorly by all candidates.

What information is provided by ¹H NMR, MS and IR for an organic compound?

I.   ¹H NMR: chemical environment(s) of protons
II.  MS: fragmentation pattern
III. IR: types of functional group

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

D

A liquid was added to a graduated cylinder. What can be deduced from the graph?

B

The enthalpy of combustion of ethanol is determined by heating a known mass of tap water in a glass beaker with a flame of burning ethanol.

Which will lead to the greatest error in the final result?

A.     Assuming the density of tap water is 1.0 g cm⁻³

B.     Assuming all the energy from the combustion will heat the water

C.     Assuming the specific heat capacity of the tap water is 4.18 J g⁻¹ K⁻¹

D.     Assuming the specific heat capacity of the beaker is negligible

B

Which value of q, in J, has the correct number of significant figures?

q = mcΔT

where m = 2.500 g, c = 4.18 J g⁻¹ K⁻¹ and ΔT = 0.60 K.

A.     6

B.     6.3

C.     6.27

D.     6.270

B

What is the name of this compound using IUPAC rules?

A. 2,3-diethylbutane

B. 2-ethyl-3-methylpentane

C. 3-methyl-4-ethylpentane

D. 3,4-dimethylhexane

D

This was the easiest question on the paper. 94% of the candidates recognized the correct IUPAC name of the compound.

Data collected from a larger number of silicon samples could also be plotted to determine the density using the following axes.

Which statements are correct?

    I. The density is the slope of the graph.
    II. The data will show that mass is proportional to volume.
    III. The best-fit line should pass through the origin.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

D

This question was answered in two different ways. 33 % of the candidates chose the correct answer (D) considering what would be true about a mass-volume graph for silicon samples. However, 39 % chose distractor (B) as they considered the silicon samples in the previous question which did not show a directly proportional relationship. Both answers were accepted as we agree that the wording was ambiguous (it will be amended before publication).

The dotted line represents the formation of oxygen, O₂(g), from the uncatalysed complete decomposition of hydrogen peroxide, H₂O₂ (aq).

Which curve represents a catalysed reaction under the same conditions?

B

Graphical representation of catalysis was also well answered.

The rate of a reaction is studied at different temperatures.

Which is the best way to plot the data?

C

What is the slope of the graph?

A.  −0.0025 mol dm⁻³s⁻¹

B.  −0.0025 mol dm⁻³s

C.  −0.0033 mol dm⁻³s⁻¹

D.  −0.0033 mol dm⁻³s

A

What are the absolute and percentage uncertainties for the change in mass?

Initial mass: 22.35 ±0.05 g

Final mass: 42.35 ±0.05 g

B

Consider the mass spectrum of an element:

What is the relative atomic mass of this element?

A.  10.2

B.  10.5

C.  10.8

D.  10.9

C

Burette readings for a titration are shown.

What is the mean titre?

A.  11.1 cm³ ± 0.1 cm³

B.  11.15 cm³ ± 0.05 cm³

C.  11.2 cm³ ± 0.05 cm³

D.  11.2 cm³ ± 0.1 cm³

D

What is the index of hydrogen deficiency (IHD) of this molecule?

Paracetamol (acetaminophen)

A.  3

B.  4

C.  5

D.  6

C

What is the value of the temperature change?

Initial temperature: 2.0 ± 0.1 °C

Final temperature: 15.0 ± 1.0 °C

A. 13.0 ± 0.1 °C

B. 13.0 ± 0.9 °C

C. 13.0 ± 1.0 °C

D. 13.0 ± 1.1 °C

D

Which quantity is likely to be the most inaccurate due to the sources of error in this experiment?

A.  Mass of ethanol burnt

B.  Molecular mass of ethanol

C.  Mass of water

D.  Temperature change

D

What can be deduced from the infrared (IR) spectrum of a compound?

A. Number of hydrogens

B. Number of hydrogen environments

C. Bonds present

D. Molar mass

C

71 % of the candidates identified the bonds present as the information that can be deduced from an infrared spectrum. The most commonly chosen distractor was B (the number of hydrogen environments).

What is the ratio of areas under each signal in the ¹H NMR spectrum of 2-methylbutane?

A.   6 : 1 : 2 : 3

B.   3 : 3 : 1 : 5

C.   6 : 1 : 5

D.   3 : 3 : 1 : 2 : 3

A

20 cm³ of 1 mol dm⁻³ sulfuric acid was added dropwise to 20 cm³ of 1 mol dm⁻³ barium hydroxide producing a precipitate of barium sulfate.

H₂SO₄(aq) + Ba(OH)₂(aq) → 2H₂O (l) + BaSO₄(s)

Which graph represents a plot of conductivity against volume of acid added?

B

The question involved the formation of a precipitate – not a familiar concept to the candidates. It required candidates (to work out how the number of ions and hence conductivity were changing. 37% of the candidates got the correct answer (conductivity decreased as volume of H₂SO₄ increased). The majority increased conductivity as H₂SO₄ was added.

Which compound produces this mass spectrum?

^{[Spectral Database for Organic Compounds, SDBS. SDBS Compounds and Spectral Search. [graph] Available at:
https://sdbs.db.aist.go.jp [Accessed 3 January 2019].]}

C

Question 29 contained a mass spectrum and 44% of students chose the correct answer of C - ethanoic acid. There were comments that this was unfair without access to the data booklet. However, as the other molecules are clearly wrong this did not seem so difficult to do without the data booklet as they did have the periodic table.

Which spectra would show the difference between propan-2-ol, CH₃CH(OH)CH₃, and propanal, CH₃CH₂CHO?

I.   mass
II.  infrared
III. ¹H NMR

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

D

Which information can be gained from an infrared (IR) spectrum?

A.     Ionization energy of the most abundant element

B.     Number of different elements in the compound

C.     Bonds present in a molecule

D.     Molecular formula of the compound

C

How should a measurement of 5.00 g from a balance be recorded?

A. 5.00 ± 0.1 g

B. 5.00 ± 0.01 g

C. 5.00 ± 1 g

D. 5.00 ± 0.001 g

B

80 % of candidates could correctly identify uncertainty.

What can be deduced from the following ¹H$$NMR spectrum?

A.     There is only one hydrogen atom in the molecule.

B.     There is only one hydrogen environment in the molecule.

C.     The molecule is a hydrocarbon.

D.     There is only one isotope in the element.

B

The following data were recorded for determining the density of three samples of silicon, Si.

Which average density value, in g cm⁻³, has been calculated to the correct number of significant figures?

A. 2

B. 2.3

C. 2.27

D. 2.273

B

This question about choosing the answer to a calculation with the appropriate number of significant figures discriminated well between high-scoring and low-scoring candidates. Candidates found this question relatively challenging and only 62 % chose the answer with two significant figures. The most commonly chosen distractor was C which expressed the answer to three significant figures.

Which is correct for the spectra of organic compounds?

A.   Mass spectroscopy provides information about bond vibrations.

B.   ¹H NMR spectroscopy provides the values of carbon–hydrogen bond lengths.

C.   Infrared spectroscopy provides the number of hydrogen atoms.

D.   Mass spectroscopy provides information about the structure.

D

What is the index of hydrogen deficiency (IHD) for this molecule? 

A. 3

B. 4

C. 5

D. 6 

D