Describe what happens to plane-polarized light when it passes through a solution of an optically active compound.

A mixture of enantiomers shows optical rotation.

Suggest a conclusion you can draw from this data.

plane of polarization is rotated

Award zero if answer refers to plane-polarized light being bent.

[1 mark]

not a racemic mixture
OR
two enantiomers not equimolar
OR
mixture contains optically active impurity
OR
relative proportions of enantiomers in mixture can be determined

[1 mark]

Deduce equations for the following nuclear reactions:

(i) Molybdenum-98 absorbs a neutron.

(ii) The isotope produced in (a) (i) decays into technetium-99m.

Molybdenum-99 has a half-life of 66 hours, while technetium-99m has a half-life of 6 hours. Outline why technetium-99m is made on-site.

Outline two reasons, other than its half-life, why technetium-99m is so useful in medical diagnosis.

Outline the nature of the radioactive waste that is generated by the use of technetium-99m in medical diagnosis.

i

${}_{42}^{98}\mathrm{M}\mathrm{o}$ + ${}_0^1\mathrm{n}$ → ${}_{42}^{99}\mathrm{M}\mathrm{o}$

Accept ⁹⁸Mo + ¹n/n → ⁹⁹Mo.

ii

${}_{42}^{99}\text{Mo}\to {}_{43}^{99\text{m}}\text{Tc}+{}_{-1}^0\beta$

Accept “ ${}_{-1}^{0}e$” for “ ${}_{-1}^0\beta$”.

Accept “ ${}^{99}Mo\to {}_{}^{99\text{m}}Tc+\beta$”.

Accept “ ${}_{-1}^{0}e/e^{-}/e$” for “$\beta$”.

Do not penalize “ ${}_{}^{99}Tc$” for “ ${}_{}^{99\text{m}}Tc$”.

molybdenum-99 can be easily transported «before it decays»/more stable
OR
«most of» technetium-99m will decay during transportation

Do not accept just “short half-life of Tc-99m”

emits gamma rays
OR
emissions escape from body
OR
emissions detected by gamma camera
OR
radiation dose is low

chemically reactive/versatile/transition metal bonds to a range of «biologically active» substances

Do not accept “short half-life of Tc-99m”.
Accept “energy of photons produced is «relatively» low” and “no high energy beta emission” for M1.
Accept “…has ability to form tracers” for “…bonds to a range of «biologically active» substances".

low-level «radioactive» waste/LLW
OR
small amounts of ionizing radiation for short time

Omeprazole exists as a racemic mixture whereas esomeprazole is a single enantiomer. Outline how, starting from a non-chiral molecule, esomeprazole but not omeprazole, could be synthesized. Details of chemicals and conditions are not required.

Any two of:

chiral molecule/auxiliary/optically active species is used/added/connected «to the starting molecule to force reaction to follow a certain path»

chiral intermediate forms «only» one enantiomer
OR
auxiliary creates stereochemical condition «necessary to follow a certain pathway» / stereochemical induction
OR
existing chiral centre affects configuration of new chiral centres

«after new chiral centre created» chiral auxiliary removed «to obtain desired product»

Both spectra show a peak at wavenumber 1700 cm^–1. Identify the bond responsible for this peak.

Deduce which spectrum belongs to paracetamol, giving two reasons for your choice. Use section 26 of the data booklet.

Describe how mild analgesics function.

C=O

Accept “carbonyl”.

X (must be identified) AND

Any two of:

For X:

N–H «absorption» AND at 3300 – 3500 «cm^–1» ✔

O–H «absorption» in phenol AND at 3200 – 3600 «cm^–1» ✔

absence of OH «absorption» in carboxylic acid AND 2500 – 3000 «cm^–1»

Accept any specific wavenumber in the range 3300–3380 «cm^–1» for M1.

Accept any specific wavenumber in the range 3100–3200 «cm^–1».

Award [1 max] if Y is incorrectly identified for paracetamol but if a correct reason/reasons is/are given for the bond absorption(s).

[Max 2 Marks]

prevents/interferes with the production of prostaglandins

OR

prevents/interferes with the production of substances responsible for inflammation/pain/fever at the site of injury/source of pain

Fuel cells use an electrochemical process to determine the concentration of ethanol.

Formulate the overall equation for this process.

Predict the chemical shifts and integration for each signal in the ¹H NMR spectrum for ethanol using section 27 of the data booklet.

C₂H₅OH(g) + O₂(g) → CH₃COOH(aq) + H₂O(l)

Accept any correct formula for reactants and products.

[1 mark]

R–OH:

1.0–6.0 «ppm» AND 1 H

R–O–CH₂–:

3.3–3.7 «ppm» AND 2 H

–CH₃:

0.9–1.0 «ppm» AND 3 H

Award [1] for the ratio of 1:2:3 (in any order).

Award [2] for three correct chemical shifts without integration.

Award [1] for two correct chemical shifts without integration.

For each chemical shift accept a specific value within the range.

Assignment of proton to fragment (eg, R–OH) is not required in each case.

[3 marks]

Suggest what may have led to these changes in acceptable concentrations.

One class of performance-enhancing drugs is the anabolic steroids. Detection of these drugs in urine samples uses a combination of gas chromatography and mass spectrometry (GC/MS).

(i) Describe how gas chromatography enables the components of urine to be analysed.

(ii) The structures of two steroids, testosterone and nandrolone, are given below.

With reference to the molar masses of the two steroids, determine, with a reason, which can be identified from the mass spectrum below.

improvements in technology/instrumentation/analytical techniques/precision of measurements

Accept “greater awareness/knowledge of the negative effects of the drugs”.

i

«components have» different affinities for/partition between 2 phases/mobile and stationary phase  

move at different rates through instrument
OR
have different retention times

ii

nandrolone M = 274 «g mol^–1»
OR
testosterone M = 288 «g mol^–1»

nandrolone identified because «molecular ion peak of» m/z = 274 

Accept non-integer molar masses, ie, 274.44 «g mol^–1» and 288.47 «g mol^–1».

Accept also “m/z = 275” for “m/z = 274” in M2.

Accept “absence of peak with m/z = 288”

Suggest why aspirin is slightly soluble in water. Refer to section 37 of the data booklet.

A student prepares aspirin from salicylic acid in the laboratory, extracts it from the reaction mixture, ensures the sample is dry and determines its melting point.

Suggest why the melting point of the student’s sample is lower and not sharp compared to that of pure aspirin.

Organic molecules can be characterized using infrared (IR) spectroscopy.

Compare and contrast the infrared peaks above 1500 cm⁻¹ in pure samples of aspirin and salicylic acid using section 26 of the data booklet.

Some mild analgesics contain a solid mixture of acidic aspirin and a non-acidic organic chemical of similar polarity to asprin.

Discuss how acid-base properties and the process of solvent extraction can be used to separate aspirin from the mixture.

The pharmaceutical industry is one of the largest producers of waste solvents.

State a green solution to the problem of organic solvent waste.

presence of «large» benzene/arene ring AND non-polar/hydrophobic
OR
presence of «large» benzene/arene ring AND cannot form H-bond with water

contain COOH/carboxyl/–OH/hydroxyl «and ester group» AND polar/hydrophilic
OR
contain COOH/carboxyl/–OH/hydroxyl «and ester group» AND can form H-bonds with water

Accept “phenyl” for “benzene ring”.

Accept "carboxylic acid" for "carboxyl".

Do not accept "alcohol" for "hydroxyl".

[2 marks]

«student’s» sample impure

lattice disrupted/not uniform «due to presence of impurities»
OR
fewer interparticle/intermolecular forces «due to presence of impurities»

Accept converse arguments.

[2 marks]

One similarity:
peak at 2500–3000 «cm^–1»/peak due to O–H/hydroxyl in carboxylic acids
OR
peak at 1700–1750 «cm^–1»/peak due to C=O/carbonyl
OR
peak at 2850–3090 «cm^–1»/peak due to C–H of arene

One difference:
peak at 3200–3600 «cm^–1» in salicylic acid/ peak due to O–H in phenol in salicylic acid
OR
«two» peaks at 1700–1750 «cm^–1» in aspirin AND one peak «in the same area» in salicylic acid

Accept “peak at 1600 cm^–1 for arene/benzene ring” – not in the data booklet.

Accept “2500–3600 cm^–1 «overlapping absorptions of two O–H» in salicylic acid”.

Accept “stronger/broader/split peak at 1700–1750 cm^–1 in aspirin”.

[2 marks]

dissolve compounds in an organic solvent

add NaOH(aq)/OH^–(aq) «to the mixture» to convert aspirin to its water soluble salt

separate the two «immiscible» layers

convert salt «in aqueous layer» back to aspirin by reacting with acid/H⁺

«evaporate solvents and dry»

Accept organic solvents immiscible with water such as hexane, ethyl ethanoate, butyl acetate.

Accept any other base.

Need explanation for mark.

[3 marks]

«use of» alternative solvents such as supercritical/liquid CO₂
OR
use of water «as solvent»
OR
solvent-free reactions «for example, polymerization of propene»
OR
solid-state chemistry
OR
recycle «waste» solvents
OR
catalysis that leads to better/higher yield
OR
reducing number of steps

Do not accept political/regulatory solutions.

“catalysis” not sufficient for mark.

[1 mark]

State the type of radiation technetium-99m emits.

Discuss the properties that make a radioisotope suitable for diagnosis.

Describe the proper disposal of low-level radioactive waste in hospitals.

Technetium-99m has a half-life of $6.03$ hours. Calculate the amount of $1.00\times {10}^{-11} \mathrm{mol}$ of technetium-99m remaining after $48.0$ hours.

gamma/$\gamma$ ✔

Any three of:

«easily» detected/traced
OR
«gamma-radiation of approximately» same frequency as X-rays «so can be detected using existing X-ray equipment» ✔

short/intermediate half-life «hence does not remain in body for long time» ✔

weak ionizing radiation «less harmful»
OR
low amount of radiation produced «so less harmful»
OR
energy of photons is low ✔

form «variety of» compounds that are absorbed by «different» organs
OR
«chemically» binds to many biologically active compounds ✔

excreted quickly «from body» ✔

store until material becomes inactive/radiation levels drop ✔

dispose with other waste
OR
dispose in landfills ✔

Only award M2 if M1 correct.

Accept “dispose by incineration” for M2.

Alternative 1:

$«N=N_0(0.5{)}^{\frac{t}{t_{\mathit{1}\mathit{/}\mathit{2}}}}=»1.00\times {10}^{-11}\times {\left(0.5\right)}^{\frac{48.0}{6.03}}$ ✔

$«\mathrm{N}=»4.02\times {10}^{-14} «\mathrm{mol}»$ ✔

Alternative 2:
$«\lambda =\frac{\ln 2}{6.03}=»0.115«{\mathrm{hr}}^{-1}»$ ✔

$«N=N_0{e}^{-\lambda t}=1.00\times {10}^{-11}\times e^{-0.115\times 48}=»4.01\times {10}^{-14} «\mathrm{mol}»$ ✔

Award [2] for correct final answer.

This question was well answered. Most were able to state that gamma radiation is emitted from technetium-99m. The most common incorrect answer was beta radiation.

Some excellent answers were seen for this question; often candidates were hitting four of the assigned marking points, though a few candidates confused diagnosis and radiotherapy. Nearly everyone got a mark for "short half-life", however. This question was much better answered than in previous sessions.

Surprisingly, this question caught out several candidates and the marks varied from zero to one to two. To score full marks, candidates first had to state that the proper disposal of low-level radioactive waste (LLW) in hospitals involves storing the material until such time as radiation levels drop. Then the material can be disposed of in landfills for example. A number failed to outline the first point and some also mixed up LLW with HLW.

The question on half-life was very well answered and nearly all scored full marks, often via different methods of calculation of the amount of technetium-99m remaining after a period of 48 HRS.

Explain how zanamivir works as a preventative agent against flu viruses.

Circle the side-chain in penicillin on the structure below.

Explain, with reference to the action of penicillin, why new penicillins with different side-chains need to be produced.

State and explain the relative solubility of codeine in water compared to morphine and diamorphine.

State the natural source from which codeine, morphine and diamorphine are obtained. 

Circle two chiral carbons in the section of the Taxol structure below.

«drug» blocks/inhibits «viral» enzyme/neuraminidase/$\mathrm{NA}$ «activity» ✔

prevents virus from leaving/escaping host cells «thus cannot infect other cells» ✔

Do not accept other anti-viral methods (as question is specific to Zanamivir).

   ✔

Accept a circle that does not surround the amido group.

Do not accept a circle that only surrounds the phenol group.

bacterial resistance «to older penicillins/antibiotics» ✔

prevent penicillinase/beta-lactamase/enzyme in bacterium to deactivate/open penicillin/beta-lactam ring ✔

Accept “antibiotic resistant bacteria” but not “antibiotic resistance” for M1.

Accept “reduce allergic reactions from penicillin” for M2.

Award [1 max] for “increased efficiency” OR “increased stability in GIT”.

Do not accept “bacteria develop tolerance”.

codeine less soluble «in water» than morphine AND more soluble than diamorphine
OR
morphine > codeine > diamorphine «in terms of solubility in water» ✔

more/stronger/greater hydrogen/H bonding «due to more hydroxyl groups leads to greater solubility» ✔

opium poppy/plants/seeds ✔

Accept “poppy” OR “opioid”.

any two chiral carbons identified ✔

In this question candidates were required to describe how the mixture can be separated by fractional distillation. Only the better candidates scored both marks, though most gained at least one mark, usually for stating that the most volatile component is collected first. Many did not convey the idea that there is continuous evaporation and condensation in the process or the fact that the temperature decreases up the fractionating column.

Most were able to circle the side-chain in penicillin. Common errors included circling only the phenolic group, the four-membered ring or the five-membered ring.

This question was well answered though many lost M1 for stating "antibiotic resistance" instead of mentioning "bacterial resistance".

Only the better candidates were able to state and explain the relative solubility of codeine in water compared to morphine and diamorphine. The majority scored M1 for the correct order of relative solubility. Few gave a comprehensive explanation outlining that there is greater hydrogen bonding due to more hydroxyl groups, which results in greater solubility.

The natural source from which codeine, morphine and diamorphine are obtained had to be stated. Most scored the single mark here for "poppy". Common errors included "willow tree" or "opium" alone, which was not deemed sufficient to score the mark.

The idea of a chiral carbon was very well understood and nearly all scored the mark for identifying any two chiral carbons in Taxol.

Yttrium-90 is used in treating certain cancers.

Formulate a nuclear equation for the beta decay of yttrium-90.

Lutetium-177 is a common isotope used for internal radiation therapy.

Suggest why lutetium-177 is an ideal isotope for the treatment of certain cancers based on the type of radiation emitted.

Calculate the rate constant, $\lambda$, in day⁻¹, for the decay of iodine-131 using section 1 of the data booklet.

Calculate the time, in days, for 90% of the sample to decay.

A breathalyser measures the blood alcohol content from a breath sample. Formulate half-equations for the reactions at the anode (negative electrode) and the cathode (positive electrode) in a fuel cell breathalyser.

⁹⁰Y → ⁹⁰Zr + β^–

Accept β, e or e^–.
Accept ⁹⁰Y → ⁹⁰Zr + β^– + v

[1 mark]

beta-radiation/emission AND targets tumour/cancer cells
OR
beta-radiation/emission AND limited damage to healthy cells/tissues
OR
beta-radiation/emission AND produces «small amount of» gamma-rays «for visualizing tumours/monitoring treatment»

[1 mark]

$\lambda \left(=\frac{\ln 2}{t_{\frac{1}{2}}}=\frac{0.693}{8.02day}\right)=8.64\times {10}^{-2}/0.0864$ «day⁻¹»

[1 mark]

ALTERNATIVE 1:
«N₀ = initial amount = 100%»

N «= 100 – 90» = 10% at time t

«$\ln \left(\frac{100}{10}\right)=2.303=0.0864t$»

«$t=\frac{2.303}{0.0864\text{ da}{\text{y}}^{-1}}=$» 26.7 «days»

Accept 26.6 or 27 «days»
Award [2] for correct final answer.

ALTERNATIVE 2:
«N_t = N₀(0.5)ⁿ where n = number of half-lives»

10 = 100(0.5)ⁿ

«$\log \left(\frac{1}{10}\right)=n\times \log 0.5$»

«$-1=n\left(-0.301\right)/n=\frac{1}{0.301}$»

«t $=\frac{1}{0.301}\times 8.02=$» 26.6 «days»

Accept 26.7 or 27 «days»

Award [2] for correct final answer.

[2 marks]

Anode (negative electrode): C₂H₅OH + H₂O → CH₃COOH + 4H⁺ + 4e^–

Cathode (positive electrode): O₂ + 4H⁺ + 4e^– → 2H₂O

[2 marks]

Explain why alpha-radiation is particularly suitable for this treatment.

Outline how the alpha-radiation in TAT is directed to cancer cells.

Identify the type of radiation emitted by these two radioisotopes.

State an equation for the one-step decay of yttrium-90.

The half-life of lutetium-177 is 6.75 days. Calculate the percentage remaining after 27 days.

more damaging than other radiation types
OR
very damaging to «cancer» cells
OR
high ionizing density «of alpha particles»

absorbed within a very short range of emission
OR
causes little damage to surrounding tissues

Accept “high ionizing power «of alpha particles»” for M1. 

Accept “low penetrating power «of alpha particles»” for M2.

[2 marks]

«radioactive isotope/radionuclide/alpha-emitter» administered using carrier drug/protein/antibodies

[1 mark]

beta/β «radiation»

[1 mark]

${}_{39}^{90}Y\to {}_{40}^{90}Zr+\beta$

Accept "${}_{-1}^{0}e/e/e^{-}$" OR "${}_{-1}^0\beta /{\beta }^{-}$"

Accept ECF from (b) (i) if incorrect radiation identified, eg, ${}_{39}^{90}Y{\to }_{37}^{86}Rb{+}_2^{4}He$

[1 mark]

ALTERNATIVE 1:
«4 half-lives»
6.25 «%»

ALTERNATIVE 2:
«N_t = N₀${\left(0.5\right)}^{\frac{t}{t_{1/2}}}=100{\left(0.5\right)}^{\frac{27}{6.75}}=$» 6.25 «%»

[1 mark]

Deduce the structural formula of the by-product of this reaction.

Aspirin crystals are rinsed with water after recrystallization to remove impurities.
Suggest why cold water is used.

The solubility of aspirin is increased by converting it to an ionic form. Draw the structure of the ionic form of aspirin.

Comment on the risk of overdose when taking aspirin as an analgesic, referring to the following values, for a person weighing $70 \mathrm{kg}$:

Minimum therapeutic dose $=0.5 \mathrm{g}$

Estimated minimum lethal dose $=15 \mathrm{g}$

Explain how IR spectroscopy can be used to distinguish aspirin from salicylic acid.

OR

${\mathrm{CH}}_3\mathrm{COOH}$ ✔

Accept full OR condensed structural formula.

to avoid dissolving the crystals/aspirin ✔

Accept “to avoid loss of product” OR “aspirin is less soluble in cold water”.

✔

Accept a positive metal ion next to the $CO{O}^{\mathit{-}}$ such as “$N{a}^{-}\mathit{/}{K}^{\mathit{+}}$”.

Accept “$-ONa/-OK$” without showing the charges.

Accept notations such as “$RCO{O}^{-}$” OR “$RCOONa$” OR “$RCOOK$” but not “$R{O}^{-}$” OR “$RONa$” OR “$ROK$”.

low/medium risk «of overdosing» AND «estimated» lethal dose is $30$ times/much larger than therapeutic dose OR
$30$ times the dose results in chance of dying ✔

Accept “$\mathit{30}$ and low/medium risk due to large therapeutic index”.
Do not accept “low/medium risk AND large therapeutic window”.
Do not accept “$\mathit{30}$ times the dose” alone for the mark.

salicylic acid contains absorption in the range $3200-3600 «{\mathrm{cm}}^{-1}»$ ✔

due to phenol/hydroxyl/$\mathrm{OH}$ group not present in aspirin ✔

Award [2] for “additional $OH$ «stretch» in IR for salicylic acid at higher wavenumber than corresponding $OH$  «stretch» in aspirin” OR “aspirin has two absorption bands/one stronger absorption band in $\mathit{1700}\mathit{–}\mathit{1750}\mathit{ }\mathit{«}c{m}^{\mathit{–}\mathit{1}}\mathit{»}$while salicylic acid has one/weaker absorption band in that region”.

Award [1 max] for “fingerprint regions will be different for both”.

Most candidates were able to deduce a correct structural formula (either full or condensed) for ethanoic acid. A minority did not read the question fully and gave the structure of aspirin instead of the by-product of the reaction. Another incorrect answer cited as the by-product was water.

Many were unable to explain why aspirin should be washed with cold water, namely, to avoid dissolving crystals. Surprisingly, the incorrect term "melt" was frequently used instead of "dissolve".

A drawing of the structure of the ionic form of aspirin was required for this question. This question was poorly answered by a significant number of candidates, and lots of basic chemical errors were seen, such as incorrect valencies, writing RCO- instead of RCOO-, showing a cationic structure instead of an anionic structure etc. A couple of candidates also lost the mark by drawing square brackets with a negative charge both inside and outside the bracket.

Few scored this mark. Most knew the overdose risk was low but referred to a large therapeutic window instead of a large therapeutic index. Many also did not quantify the therapeutic index by working out that the estimated lethal dose is actually 30 times the therapeutic dose.

This question which asked for an explanation of how IR spectroscopy can be used to distinguish aspirin from salicyclic acid was generally very well answered. The majority stated that salicyclic acid contains an absorption in the IR spectrum in the 3200-3600 cm^-1 range due to the phenolic OH group, which is not present in aspirin. A few stated that aspirin has a methyl group and hence the CH stretch will appear in the 2850-3090 cm_-1 region of the IR spectrum in aspirin (using Section 26 of the Data Booklet) which will not appear in the corresponding IR spectrum for salicyclic acid. This is somewhat incorrect as in salicyclic acid the benzene ring will also have CH bonds and the CH stretch for the benzene ring will occur in a similar region of the IR spectrum (as indicated in Section 26 of the Data Booklet) and hence cannot be used to distinguish fully between the two structures per se if using the Data Booklet range. Of course, in practice the alkyl CH stretch would be at a slightly lower wavenumber (e.g. 2850-2950 cm^-1) in the IR spectrum compared to the aromatic CH stretch (3030 cm^-1), but virtually no candidate gave this type of precise detail.

Explain the role of the chiral auxiliary in the synthesis of Taxol.

Any three of:

chiral auxiliary is optically active

is attached to non-optically active/non-chiral substrate

creates stereochemical condition necessary to follow a certain pathway

allows only the required enantiomer to form «so avoids need to separate a racemic mixture»

[Max 3 Marks]

Taxol was originally obtained from the bark of the Pacific yew tree.

Outline how Green Chemistry has improved the process of obtaining Taxol.

Any two of:

stripping the bark kills Pacific yew tree

plant cell fermentation «and extraction»/PCF technology/use of plant cell cultures/Taxol «precursors» produced by biosynthesis/fungi/yeast/e-coli/use of natural enzymes «more sustainable process»

OR

Taxol produced semi-synthetically/Taxol from 10-DAB/10-deacetylbaccatin 

uses renewable resources

OR

use «needles/leaves/twigs of» European/common yew/yew from Himalayas

«sustainable» process has eliminated «high proportion of» hazardous chemicals/waste

OR

«sustainable» process has eliminated several solvents/«sustainable» process uses greener solvents/«sustainable» process recycles/reuses solvents

OR

«sustainable» process has eliminated several «drying» steps/«sustainable» process has eliminated lots of the work-up after the synthesis

OR

«sustainable» process has increased energy efficiency

OR

«sustainable» process has no intermediates

OR

«sustainable» process uses more efficient catalysts

Accept “Pacific yew rare/slowgrowing/takes 100/200 years to mature” for M1.

Accept “synthesis of Taxol using chiral auxiliaries increases efficiency of process as single enantiomer formed” for M4.

[2 marks]

Phosphorous-32 undergoes beta decay. Formulate a balanced nuclear equation for this process.

The half-life of phosphorus-32 is 14.3 days. Calculate the mass, in g, of ³²P remaining after 57.2 days if the initial sample contains 2.63 × 10⁻⁸ mol. Use table 1 of the data booklet and M_r = 31.97 g mol⁻¹.

Explain the targeted alpha therapy (TAT) technique and why it is useful.

³²P → ³²S + ${}_{-1}^0$β 

Accept “e^–/e/β” instead of “${}_{-1}^0$β”.

[1 mark]

ALTERNATIVE 1

«λ = $\frac{\ln 2}{14.3}$ =» 0.04847 «day^–1»

«m(³²P) = 2.63 × 10^–8 mol × 31.97 g mol^–1 × e^{–0.04847 × 57.2} =» 5.26 × 10^–8 «g»

ALTERNATIVE 2

«$\frac{57.2}{14.3}$ =» 4 «half-lives passed»

OR

«n(³²P) = $\frac{2.63\times {10}^{-8}\text{ mol}}{2^4}$ =» 1.64 × 10^–9 «mol»

«m(³²P) = 1.64 × 10^–9 mol × 31.97 g mol^–1 =» 5.26 × 10^–8 «g»

Award [2] for correct final answer.

Accept any value in the range “5.24–5.26 × 10^–8 «g»”.

[2 marks]

alpha-emitting isotopes/²¹²Pb/²²⁵Ac attached to drugs/antibodies/chelating ligands/carriers

Award [2 max] for any two of:

absorbed by «cancer/growing» cells

OR

bind to «cancer/growing» cell receptors

alpha particles have high ionizing density/power

short-range of emission «of alpha-particles»

OR

healthy tissues less affected «as slower cell growth»

OR

local effect «on dispersed/spread/metastasised cancers»

Accept “radionuclide” for “isotope”.

Accept “alpha particles are highly ionizing”.

Accept “alpha particles have low penetrating power”.

Accept “used to treat dispersed/spread/metastasised cancers” OR “can be used to map the distribution of cancer cells in the body”.

[3 marks]

State a nuclear equation to show the decay of lutetium-177.

The half-life of lutetium-177 is 6.73 days. Determine the percentage of a sample of lutetium-177 remaining after 14.0 days.

Explain the low environmental impact of most medical nuclear waste.

${}_{71}^{177}\text{Lu}\to {}_{71}^{177}\text{Hf}+{}_{-1}^0\text{e}$ «+ $\nu$»

Hf

correct A and Z AND beta product

Accept “β/ β^–/e/e^–” for “${}_{-1}^0\text{e}$”.

Accept “¹⁷⁷Lu → ¹⁷⁷Hf + e^– «+ $\nu$»”.

number of half-lives = $\frac{t}{t_{{}^{\frac{1}{2}}}}$ = 2.08

OR

$\frac{N\left(t\right)}{N_0}={0.5}^{\frac{14.0}{6.73}}$

OR

$\lambda =$ «$\frac{\text{ln}2}{t_{{}^{\frac{1}{2}}}}=\frac{\text{ln}2}{6.73}=$» 0.103 «day^–1»

OR

$\frac{N\left(t\right)}{N_0}=e^{-0.103\times 14.0}$

23.6 «%»

Award [2] for correct final answer.

Any two of:

emits weak ionising radiation

OR

low activity/radioactivity

can be stored until material becomes inactive AND then disposed with normal waste

«isotopes» have short lives

OR

exist for a short period of time

Award [1 max] for “low-level waste/LLW”.

[Max 2 Marks]

Calculate the mole fraction of ethanal in the mixture.

The vapour pressure of pure ethanal at $20°\mathrm{C}$ is $101 \mathrm{kPa}$.

Calculate the vapour pressure of ethanal above the liquid mixture at $20°\mathrm{C}$.

Describe how this mixture is separated by fractional distillation.

$«{\mathrm{\chi }}_{\mathrm{ethanal}}=\frac{0.100}{0.100+0.100+0.200}=»0.250$ ✔

Accept “$\mathit{25}\mathit{\%}$”.

$«{\mathrm{\rho }}_{\mathrm{ethanal}}=0.250\times 101=»25.3«\mathrm{kPa}»$ ✔

Any two of:
continuous evaporation and condensation
OR
increased surface area in column helps condensation ✔
Accept “glass «beads» aid condensation «in fractionating column»”.

temperature decreases up the fractionating column ✔

liquids condense at different heights
OR
liquid of lowest boiling point collected first
OR
liquid with weakest intermolecular forces collected first
OR
most volatile component collected first
OR
fractions/liquids collected in order of boiling point/volatility ✔
Accept “liquids collected in order of molar mass”.

This question involving Raoult's Law was very well answered and most were able to calculate the mole fraction of ethanal in the mixture (0.250) and the corresponding vapour pressure of ethanal above the liquid mixture at 20 °C (25.3 kPa). There was one G2 comment on this question. One teacher stated that the diagram shows four fractions but the stem of the question specifically states only three components and hence the fourth test tube is not required. The teacher commented that some students may have been distracted by this. 

This question involving Raoult's Law was very well answered and most were able to calculate the mole fraction of ethanal in the mixture (0.250) and the corresponding vapour pressure of ethanal above the liquid mixture at 20 °C (25.3 kPa). There was one G2 comment on this question. One teacher stated that the diagram shows four fractions but the stem of the question specifically states only three components and hence the fourth test tube is not required. The teacher commented that some students may have been distracted by this. 

In this question candidates were required to describe how the mixture can be separated by fractional distillation. Only the better candidates scored both marks, though most gained at least one mark, usually for stating that the most volatile component is collected first. Many did not convey the idea that there is continuous evaporation and condensation in the process or the fact that the temperature decreases up the fractionating column.

Ethanol slows down the reaction time of a driver leading to traffic accidents. Explain how the concentration of ethanol in a sample of breath can be determined using a fuel cell breathalyser.

ethanol is oxidized «to ethanoic acid»

OR

electrons are released

current/potential proportional to concentration «of ethanol»

OR

current compared to a reference «to determine concentration»

Accept “ethanol reacts with oxygen” for M1.

Accept “voltage” for “potential”.

Taxol is produced using a chiral auxiliary. Describe how the chiral auxiliary functions to produce the desired product.

chiral molecule/auxiliary/optically active species added/connected/attached «to non-chiral starting molecule to force reaction to follow a certain path»

one enantiomer produced
OR
chiral auxiliary creates stereochemical condition «necessary to follow a certain pathway»
OR
stereochemical induction
OR
existing chiral centre affects configuration of new chiral centres

«after new chiral centre created» chiral auxiliary removed «to obtain desired product»

[3 marks]

Suggest two absorbances, other than the absorbances due to the ring structure and C–H bonds, that would be present in the infrared (IR) spectrum of aspirin.

State two techniques, other than IR spectroscopy, which could be used to confirm the identity of aspirin.

Any two of:

2500–3000 «cm^–1» / «absorbance» due to O–H in carboxyl

1700–1750 «cm^–1» / «absorbance» due to C=O in carboxyl/ethanoate

1050–1410 «cm^–1» / «absorbance» due to C–O bond in carboxyl/ethanoate

Accept “carboxylic acid” for “carboxyl”, “acetate/ester” for “ethanoate”.

Accept specific wavenumber once within indicated range.

Do not award mark if reference is made to an alcohol/ether.

[2 marks]

Any two of:

melting point

mass spectrometry/MS

high-performance liquid chromatography/HPLC

NMR/nuclear magnetic resonance

X-ray crystallography

elemental analysis

Accept “spectroscopy” instead of “spectrometry” where mentioned but not “spectrum”.

Accept “ultraviolet «-visible» spectroscopy/UV/UV-Vis”.

Do not accept “gas chromatography/GC”.

Accept “thin-layer chromatography/TLC” as an alternative to “HPLC”.

[2 marks]

Hexane and propanone have vapour pressures of 17 kPa and 24 kPa respectively at 20 °C.

Calculate the vapour pressure, in kPa, at 20 °C of a mixture containing 60% hexane and 40% propanone by mole fraction, using Raoult’s law and assuming the mixture is ideal.

Explain how hexane and propanone may be separated by fractional distillation.

«vapour pressure = 0.6 × 17 + 0.4 × 24 =»

19.8 «kPa»

[1 mark]

Any three of:

different molar masses

OR

different strength of intermolecular forces

different boiling points

temperature in «fractionating» column decreases upwards

«components» condense at different temperatures/heights

OR

«component with» lower boiling point leaves column first

[3 marks]

Draw a circle around the functional group that can be converted to the carboxylate by hydrolysis.

The resulting active metabolite of oseltamivir can be detected by mass spectrometry (MS) analysis.

Deduce the mass of the expected carboxylate ion.

M_r oseltamivir = 312

Suggest a reason for using a phosphate salt of oseltamivir in oral tablets.

Anti-HIV drugs, such as zidovudine, often become less effective over time.

Explain the development of resistant virus strains in the presence of antiviral drugs.

    [✔]

Note: Accept circles that include the alkyl side chain.

283  [✔]

more soluble «in water»  [✔]

viruses undergo «rapid» mutation  [✔]

mutation causes a change in viral protein
OR
drug no longer binds to virus  [✔]

Note: Accept “rapid reproduction «allows resistant viruses to multiply»”.

Required candidates to identify the functional group in a diagram of the structure of oseltamivir that can be converted to a carboxylate by hydrolysis. This was very challenging with many varied parts of the structure circled. Many circled the amide group. Candidates who selected the ester had to be careful to not include the ring structure as well.

The challenge continued where the expected mass of the carboxylate ion was required. Some candidates chose values that exceeded the molar mass of oseltamivir itself, and some chose 45. There were very few correct answers.

Many candidates referred correctly to increased solubility of the salt in water while some mentioned bioavailability but did not realize that a salt will also form in the stomach.

Most candidates scored the first marking point when explaining the development of resistant virus strains but almost no-one scored the second mark. Many candidates were confused between bacteria and viruses and gave explanations about bacterial resistance and natural selection.

The diagram shows part of a Taxol molecule in skeletal form.

Draw a circle around each chiral carbon.

Outline how chiral auxiliaries are used to synthesize the desired enantiomer.

Explain the process of solvent extraction by which Taxol is isolated.

Do not penalize any other notation (eg *) used for a circle.

chiral auxiliary creates stereochemical condition necessary to follow a certain pathway

OR

stereochemical induction

OR

existing chiral centre affects configuration of new chiral centres ✔

chiral molecule/auxiliary/optically active species is used/added/connected to the starting molecule «to force reaction to follow a certain path»

OR

«after new chiral centre created» chiral auxiliary removed «to obtain desired product» ✔

Any two of:

immiscible solvents ✔

partitioning of Taxol between the two solvents

Taxol more soluble in one solvent ✔

extraction carried out multiple times «to improve extraction» ✔

shaking/stirring the mixture ✔

separating the two layers ✔

evaporation of the solvent from the final solution «to obtain pure Taxol» ✔

Determine the percentage of technetium-99m remaining after 24.0 hours.

Technetium-99 decays further, emitting beta radiation. Formulate the equation for the decay of technetium-99.

Outline what is meant by low-level waste.

Outline the disposal of LLW.

Magnetic resonance imaging (MRI) is an application of NMR technology using radiowaves.

Suggest why MRI is much less dangerous than imaging techniques such as X-rays and radiotracers. Use section 3 of the data booklet.

Alternative 1
half-lives = « $\frac{24}{6.0}$ =» 4.0  [✔]

«N(t) (%) = 100(0.5)⁴ =» 6.3 «%»   [✔]

Note: Accept “6.25 «%»”.

Alternative 2
λ =«$\frac{\ln 2}{t_{\frac{1}{2}}}=\frac{\ln 2}{6.0}$» 0.116 hour^–1 OR  $\frac{N_t}{N_0}$=e^{–0.116 × 24}  [✔]

6.3 «%»  [✔]

Note: Award [2] for correct final answer.

⁹⁹Tc → ⁹⁹Ru + β^–

Ru  [✔]

mass number of Ru AND beta product  [✔]

Note: Accept “e/e–/$\frac{0}{-1}$ e” for “β^–”.

small/low amounts of radiation AND for a short time  [✔]

Note: Accept “weakly ionizing radiation” instead of “small amounts of radiation”.

Accept “short half-lives” instead of “for a short time”.

stored in shielded containers until radiation level drops «to a safe level»  [✔]

lower frequency/longer wavelength/lower energy
OR
does not use ionizing radiation/radionuclides  [✔]

Note: Do not accept “does not cause cancer”.

Most candidates correctly determined the % of technetium-99m remaining after 24.0 hours. Some candidates did not read the question properly and forgot to convert to a percentage.

A common incorrect answer was to give Tc as a product or to give an incorrect symbol for beta radiation. Most candidates scored a mark for the correct mass number of the product and beta radiation.

Low level nuclear waste was poorly outlined with many superficial responses. Many candidates only gave half the required answer.

Outlining the disposal of LLW was also challenging with many candidates saying that it should be put in a container without saying the container should be shielded.

Suggesting why MRI is less dangerous than using X-rays and radiotracers was mostly answered well, but some candidates were confused and linked longer wavelengths with higher energy.

Outline how ranitidine (Zantac) inhibits stomach acid production.

Outline two advantages of taking ranitidine instead of an antacid which neutralizes excess acid.

Some antacids contain carbonates.

Determine the pH of a buffer solution which contains 0.160 mol dm⁻³ CO₃²⁻ and 0.200 mol dm⁻³ HCO₃⁻, using section 1 of the data booklet.

pK_a (HCO₃⁻) = 10.32

blocks/binds H2/histamine receptors «in cells of stomach lining»
OR
prevents histamine molecules binding to H2/histamine receptors «and triggering acid secretion»  [✔]

Any two of:
ranitidine can be effective in treating ulcers «but antacid is not»  [✔]
ranitidine can prevent long-term damage «from overproduction of acid and antacid does not» [✔]
ranitidine has a long-term effect «and antacid has short-term effect only» [✔]
ranitidine does not affect ionic balance in body «and antacid does» [✔]
ranitidine does not produce bloating/flatulence [✔]

Note: Accept “ranitidine stops the over production of acid in the stomach while antacids neutralise the excess acid
giving temporary relief” for M2.

«pH = pK_a $+\log \frac{[{\text{A}}^{-}]}{[\text{HA]}}=10.32+\log \frac{0.160}{0.200}=10.32-0.097$»
«pH =»10.22   [✔]

Some candidates were not confident enough in their answers to receive a mark while others confused the action of ranitidine which blocks H2 receptors with omeprazole which is a proton pump inhibitor.

While most candidates were awarded at least one of the two marks possible for this question some of the descriptions were too vague or incomplete to receive a mark.

This was generally a well-answered question. Most candidates who did not receive the mark inverted the concentration of the conjugate base/concentration of the acid in the calculation.

State the internal bond angles in the b-lactam ring and the expected bond angles in sp² and sp³ hybridised atoms.

Explain how the open β-lactam ring kills bacteria.

State how the structure of penicillin can be modified to combat the effect of resistance caused by over prescription.

Suggest why human cells are not affected by penicillin.

Accept “109º”.

«irreversibly» binds/bonds to enzyme/transpeptidase

OR

inhibits enzyme/transpeptidase «in bacteria» that produces cell walls

OR

prevents cross-linking of bacterial cell walls ✔

cells absorb water AND burst

OR

cells cannot reproduce ✔

Accept “reacts with” for “bonds to” for M1.

Do not accept “cell membrane” for “cell wall” for M1.

Accept “cells burst due to osmotic pressure” for M2.

Accept “bacteria” for “cells” for M2.

«modify» side-chain ✔

Accept “«modify» R”.

no cell walls

OR

humans do not have transpeptidase ✔

Identify the feature in penicillin responsible for its antibiotic activity.

The widespread use of penicillin and its derivatives has led to the appearance of resistant S. aureus strains.

Outline how these bacteria inactivate the antibiotics.

Outline how the structure of penicillin has been modified to overcome this resistance.

«four-membered» beta-lactam ring  [✔]

Note: Accept a diagram showing a structural representation of the beta-lactam ring.

produce penicillinase/enzyme that deactivates penicillin  [✔]

side-chain changed «preserving beta-lactam ring»  [✔]

Note: Accept “R group changed”.

Most candidates correctly identified the feature in penicillin responsible for its antibiotic activity.

Most candidates could outline how bacteria inactivate the antibiotics.

Outlining how the structure of penicillin has been modified was less well answered, with many candidates referring to functional groups rather than the side chain or R group.

Identify the chiral carbon atom using an asterisk, *.

Enantiomers can be identified using a polarimeter. Outline how this instrument differentiates the enantiomers.

  [✔]

«plane-»polarized light passed through sample  [✔]

analyser/second polarizer determines angle of rotation of plane of plane-polarized light
OR
each enantiomer rotates plane «of plane-polarized light» in opposite directions «by the same angle»  [✔]

Some candidates had difficulty identifying the chiral carbon in a methadone structure, with quite a few varied answers. However, many managed to mark the correct carbon.

Very poorly answered. Few scored any marks at all when outlining how a polarimeter can be used to differentiate between enantiomers. Many referred to the light or the enantiomers themselves being rotated.

Examine the synthesis of taxol in terms of green chemistry criteria.

Outline the operation of a polarimeter used to distinguish between enantiomers.

Any two of:
produced by genetically engineered/modified bacteria/E. coli
OR
sustainable because synthesized and not obtained from yew trees  [✔]

chiral auxiliaries «isolated and» reused [✔]

one enantiomer produced [✔]

toxicity/recycling of solvents/materials used [✔]

overall yield/atom economy/waste generated [✔]

Any two of:
«plane-» polarized light
OR
light passes through polarizer/polarizing filter  [✔]

enantiomers rotate plane of «plane-» polarized light «by equal angles» in opposite directions [✔]

measure angle/direction of rotation [✔]

The synthesis of taxol in terms of green chemistry criteria invited varied responses. While some candidates were precise in their answers but others lost focus and wrote something about green chemistry.

The operation of a polarimeter to distinguish between enantiomers was generally well handled by the candidates while some missed stating to measure the angle/direction of rotation.

Outline one way in which antiviral drugs work.

Discuss two difficulties associated with solving the AIDS problem.

Any one of:
alter cell’s genetic material so that virus cannot use it to multiply  [✔]

prevent viruses from multiplying by blocking enzyme activity within host cell
OR
inhibit the synthesis of viral components by blocking enzymes inside the cell [✔]

prevent viruses from entering «host» cell
OR
bind to cellular receptors targeted by viruses
OR
bind to virus-associated proteins/VAPs which target cellular receptors
OR
prevents removal of protein coat/capsid
OR
prevents injection of viral DNA/RNA into cell [✔]

prevent/hinder the release of viruses from the cell [✔]

Note: Accept “prevents synthesis of virus by host cell”.

Accept “alters RNA/DNA/genetic material of virus”.

Do not accept just “mimics nucleotides”.

Any two of:
viruses lack cell structure so difficult to target with drugs  [✔]

HIV is a retrovirus
OR
HIV genetic material is in the form of RNA instead of DNA [✔]

HIV affects/destroys helper/T-cells which are necessary to fight infection [✔]

HIV has great genetic diversity so difficult to produce «a» vaccine [✔]

anti-retroviral agents are expensive so not everyone/country can afford them [✔]

socio-cultural issues deter people from seeking treatment/prevention/diagnosis
OR
lack of education/conversation/stigma associated with being HIV-positive [✔]

mutation of virus/HIV [✔]

virus/HIV metabolism linked to that of host cell [✔]

drugs harm host cell as well as virus/HIV [✔]

HIV difficult to detect/remains dormant [✔]

Candidates responded fairly well to this question. Candidates who did not receive a mark were either too vague or discussed anti-bacterial methods.

Most candidates were awarded at least one of the two marks possible for this question. Some student responses were too vague or discussed the social and political issues surrounding the AIDS crisis. There were also some responses, which only talked about AIDS extensively with no mention of the virus.

State the feature of Taxol that is a major challenge in its synthesis. Use section 37 of the data booklet.

Describe how the challenge in (a) was resolved by pharmaceutical companies.

numerous stereoisomers/chiral carbons/chiral centres/stereocentres/optical isomers ✔

NOTE: Accept exact number of chiral carbons ie 11, but do not accept just “chiral”.

chiral auxiliaries/molecule binds to reactant blocking one reaction site «by steric hindrance»
OR
asymmetric synthesis / enantioselective catalysis «producing a specific enantiomer»
OR
biosynthesis / genetically modified bacteria/microorganisms ✔

NOTE: Accept “use of a chiral auxiliary leading to «the synthesis of» the desired enantiomer”.

Predict one absorption band present in an infrared (IR) spectrum of aspirin, using section 26 of the data booklet.

Determine the mass of aspirin which reacted with 16.25 cm³ of 0.100 mol dm⁻³ NaOH solution.

Determine the percentage purity of the synthesized aspirin.

Outline how aspirin can be chemically modified to increase its solubility in water.

State why aspirin should not be taken with alcohol.

Any one of:
1050–1410 «cm^–1 due to C–O»  [✔]
1700–1750 «cm^–1 due to C=O in acids and esters» [✔]
2500–3000 «cm^–1 due to O–H in acids» [✔]
2850–3090 «cm^–1 due to C–H in alkanes and arenes» [✔]

n(aspirin) «= n(NaOH) = $\frac{16.25\text{ c}{\text{m}}^3}{\text{1000}}$ × 0.100 mol dm–3 »= 1.625 × 10^–3 «mol»  [✔]

m(aspirin) «= 1.625 × 10^–3 mol × 180.17 g mol^–1 »= 0.293 «g»  [✔]

Note: Award [2] for correct final answer.

« $\frac{0.293\text{ g}}{\text{0}\text{.300 g}}$ × 100 % »= 97.7 «%»  [✔]

convert to a salt
OR
react with sodium hydroxide  [✔]

Note: Accept other reactions forming soluble salts.

Accept “to ionize” but not “more polar”.

synergistic effect/increased toxicity
OR
increased risk of stomach/intestines bleeding/ulcers/heartburn
OR
increased risk of liver toxicity/damage
OR
increased risk of nausea/vomiting   [✔]

This was a very well answered question. Even weak candidates were able to identify one correct absorption band present in an infrared spectrum of aspirin.

A significant number of candidates were able to calculate the mass of aspirin correctly.

A significant number of candidates were able to calculate the percentage purity of aspirin correctly although some managed an ECF mark.

This part was reasonably answered by most candidates.

This part was well answered by the majority of the candidates.

Explain why diamorphine (heroin) crosses the blood–brain barrier more easily than morphine.

Outline the meaning of the bioavailability of a drug.

blood-brain barrier is hydrophobic/non-polar/made of lipids ✔

morphine has hydroxyl/OH «groups»/is more polar AND diamorphine has ester/ethanoate/OCOCH₃/acetate «groups»/is less polar/is lipid soluble ✔

Accept “fats” for “lipid”.

Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.

Accept “non-polar” for “less polar” in M2.

fraction/proportion/percentage of «administered dosage» enters blood/plasma/circulation ✔

Accept “fraction/proportion/percentage of «administered dosage» that reaches target «part of human body»”.

Explain how opiates act to provide pain relief.

Discuss how the difference in structure of two opiates, codeine and morphine, affect their ability to cross the blood–brain barrier. Use section 37 of the data booklet.

«temporarily» bond/bind to «opioid» receptors in the brain/CNS  [✔]

block the transmission of pain impulses  [✔]

«codeine crosses blood–brain barrier more easily» morphine has more hydroxyl/OH «groups than codeine»  [✔]

codeine/ether group is less polar
OR
hydroxyl/OH «groups in morphine» H-bond to water  [✔]

Note: Award [1 max] if no statement or an incorrect statement about the blood–brain barrier.

The question asked candidates to explain how opiates provide pain relief. This was difficult and was poorly answered by many. As this has been asked many times over the years, it would be an advantage to candidates to practise answering past examination questions.

The explanation that required a discussion of the difference in structure of codeine and morphine, and how this affects their ability to cross the blood-brain barrier was challenging. Many scored for saying “codeine is less polar”. Some also scored for saying that “morphine has more hydroxyl groups” but others provided less detail and could not be awarded any marks.

Alpha particles are more damaging to human cells than any other nuclear radiation and yet they are used in targeted alpha therapy (TAT).

Explain how TAT is relatively safe to use in the treatment of dispersed cancers.

Technetium-99m (${}_{43}^{99\text{m}}\text{Tc}$) has a half-life of 6.0 hours. Calculate the percentage of ${}_{43}^{99\text{m}}\text{Tc}$ remaining in a sample of the radioisotope after two days.

Suggest why the percentage of technetium-99m remaining in the human body two days after injection will be lower than that calculated in (b)(i).

«alpha emitter» carried to/selectively absorbed by cancer cells «by antibody, carrier drug, protein» ✔

low penetrating power

OR

short range ✔

Do not accept just “targets cancer cells and does not affect healthy cells”.

ALTERNATIVE 1:

«$\frac{40}{6.0}$ =» 8 $t_{\frac{1}{2}}$/8 half-lives «required» ✔

% remaining = «(0.5)⁸ × 100 =» 0.39 «%» ✔

ALTERNATIVE 2:

λ = «$\frac{0.693}{6.0}$ =» 0.1155 ✔

% remaining = «100 × e^{–0.1155 × 48} =» 0.39 «%» ✔

Award [2] for correct final answer.

Accept “0.32 «%»” in ALTERNATIVE 2.

removed by excretion ✔

Accept any method of excretion.

Many drugs are chiral. Explain how a polarimeter can be used to determine the relative proportion of two enantiomers.

«pure» enantiomers rotate the plane «of plane-»polarized light «by equal angles» in opposite directions

Any two of:

find angle of rotation of pure enantiomers

measure angle of rotation of mixture

mixture has angle between that of two enantiomers

ratio of angles gives purity

[3 marks]

Formulate an equation for the neutralization of stomach acid with calcium carbonate, CaCO₃ (s).

Acid secretion can be regulated by other types of drugs such as omeprazole and ranitidine. Outline how each of these drugs acts to reduce excess stomach acid.

Omeprazole:

Ranitidine:

CaCO₃ (s) + 2HCl (aq) → CO₂ (g) + CaCl₂ (aq) + H₂O (l)   [✔]

Note: Accept balanced ionic equations involving “H⁺” or “H₃O⁺”.

Do not accept “H₂CO₃”.

Omeprazole:
inhibits enzyme/«gastric» proton pump «which secretes H⁺ ions into gastric juice»
OR
inhibits the H⁺/K⁺-ATPase system   [✔]

Ranitidine:
inhibits/blocks H2/histamine receptors «in cells of stomach lining»
OR
prevents histamine binding to H2/histamine receptors «and triggering acid secretion»  [✔]

Note: Accept “H2-receptor antagonist” for M2.

Responses were mixed with some candidates easily writing an equation for the neutralization of stomach acid with CaCO₃. Others failed to score for having incorrect products such as H₂CO₃ or CaCl, or for using sulfuric acid instead of hydrochloric for stomach acid.

Many candidates correctly outlined how drugs such as omeprazole and ranitidine regulate acid secretion.

Distinguish between therapeutic window and therapeutic index in humans.

Therapeutic window:

Therapeutic index:

Explain why diamorphine (heroin) is more potent than morphine using section 37 of the data booklet.

Therapeutic window:
range of dosage «over which a drug» provides the therapeutic/desired effect without causing adverse/toxic effects  [✔]

Therapeutic index:
toxic dose of drug for 50 % of population divided by minimum effective dose for 50 % of population
OR
$\frac{\text{TD50}}{\text{ED50}}$  [✔]

Note: M1 may be scored from a correctly labelled diagram.

Do not accept reference to lethal dose used in therapeutic index in animal studies.

morphine has «two» hydroxyl groups AND diamorphine has «two» ester/ethanoate/acetate groups
OR
molecule of diamorphine is less polar than morphine
OR
groups in morphine are replaced with less polar/non-polar groups in diamorphine  [✔]

«less polar molecules» cross the blood–brain barrier faster/more easily
OR
diamorphine is more soluble in non-polar environment of CNS/central nervous system than morphine  [✔]

Note: Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.

Accept “fats” for “lipid”.

Accept “heroin” for “diamorphine”.

Most candidates receive one mark for this question, mainly for the therapeutic window. Some candidates inverted the ratio as ED50/TD50 for therapeutic index.

This part was reasonably well answered with some very good answers.

Outline how ranitidine (Zantac) functions to reduce stomach acidity.

Blocks/binds H2-histamine receptors «in cells of stomach lining»
OR
prevents histamine molecules binding to H2-histamine receptors «and triggering acid secretion»

Accept “H2 receptor antagonist”

[1 mark]

Evaluate the suitability of technetium-99m for this use.

Calculate the percentage of technetium-99m remaining after 10.0 hours. Use section 1 of the data booklet.

Any two of:
can be readily “tagged” to variety of biologically active carriers «which will deliver it to specific locations for imaging uses»  [✔]

frequency of radiation is compatible with existing X-ray detection apparatus [✔]

product of decay has low radioactivity/relatively short half-life/low total exposure to patient [✔]

«but small» increased risk of cancer to patient [✔]

must be made on site [✔]

Note: Accept other valid answers outlining advantages or limitations of Tc-99m, such as “produces only LLW”, “Tc is a transition element forming compounds in a variety of oxidation states”, “gamma-radiation «can escape the body and» be detected by external sensors”, “activity decreases quickly, so dose must be calculated prior to each injection”.

ALTERNATIVE 1

$\frac{N(t)}{N_0}={\left(\frac{1}{2}\right)}^{\frac{10}{6.0}}$  [✔]
31 «% remaining» [✔]

ALTERNATIVE 2

λ «= $\frac{\ln 2}{t_{\frac{1}{2}}}$»= 0.1155 hours^–1 [✔]

«$\frac{N}{N_0}$ × 100 = e^–λt ×100 = 0.31498 × 100»

31 «% remaining» [✔]

Note: M1 is for correct substitution of values.

Award [2] for correct final answer.

The most frequent response was the short half-life, followed by the emission and detection of gamma radiation.

Most candidates were able to calculate the percentage of technetium-99m correctly.

Explain why diamorphine has greater potency than morphine.

Experimental research on both animals and humans contributes to the development of pharmaceuticals.

State the meaning of the term therapeutic index in human studies.

Any three of:
morphine has «two» hydroxyl «groups» AND diamorphine has «two» ester/ethanoate/acetate «groups» ✔

NOTE: Accept “heroin” for “diamorphine”.
Accept formulas.
Accept “hydroxy” for “hydroxyl” but not “hydroxide”.
Accept “acyl” for “ester «groups»”.

morphine is more polar than diamorphine
OR
groups in morphine are replaced with less polar/non-polar groups in diamorphine ✔

NOTE: Do not accept just “diamorphine is non-polar” for M2.

morphine is «more» soluble in blood «plasma»
NOTE: Accept “water” for “blood”.
OR
diamorphine is «more» soluble in lipids
NOTE: Accept “fats” for “lipid”.
OR
diamorphine is more soluble in non-polar environment of CNS/central nervous system than morphine ✔

diamorphine crosses the blood–brain barrier/BBB «easily» ✔

toxic dose for 50% of population divided by «minimum» effective dose for 50 % of population ✔

NOTE: Accept “TD50/ED50”.
Reference to 50% required.

Describe how a fuel cell breathalyser works.

Alcohol levels in the breath can also be determined using IR spectroscopy.

Suggest, giving a reason, which bond’s absorbance is most useful for detecting ethanol in breath.

Bond: 

Reason:

Any three of:
ethanol «in breath» is oxidized «to ethanoic acid»  [✔]
electrons pass through external circuit/meter [✔]
«to cathode where» O₂ is reduced [✔]
current is proportional to alcohol concentration [✔]

Note: Accept equations for oxidation of ethanol or reduction of oxygen.

Bond:
C–O
OR
C–H  [✔]

Reason:
cannot use O–H bonds as in water «found in breath» [✔]

Note: Accept “C–O/C–H «bonds in molecules in breath» most likely to be in ethanol”.

Do not apply ECF here.

While many scored the first marking point, full marks were rarely seen. Many candidates mixed up this and a dichromate breathalyser.

Most candidates incorrectly identified O-H, failing to realise it is unsuitable due to its abundant presence in the breath.

Explain how the beta-lactam ring is responsible for the antibiotic properties of penicillin. Refer to section 37 of the data booklet.

Outline the impact of antibiotic waste on the environment.

Suggest a concern about the disposal of solvents from drug manufacturing.

Discuss two difficulties, apart from socio-economic factors, associated with finding a cure for AIDS.

ring is «sterically» strained
OR
angles of 90° instead of 109.5/109/120° angles
OR
angles smaller than 109.5/109/120°/tetrahedral/trigonal planar/triangular planar angle ✔

ring breaks up/opens/reacts «easily»
OR
amido/amide group «in ring» is «highly» reactive ✔

«irreversibly» binds/bonds to enzyme/transpeptidase
OR
inhibits enzyme/transpeptidase «in bacteria» that produces cell walls
OR
prevents cross-linking of «bacterial» cell walls ✔

NOTE: Accept arguments using correct descriptions of hybridization for M1.
Do not accept "breaks/binds to cell walls" – a reference to the enzyme is needed for alternatives 1 and 2 for M3.
Do not accept "cell membrane" for "cell wall".

«leads to bacterial» resistance «to antibiotics»
OR
destroys useful/beneficial bacteria
OR
useful/beneficial/less harmful bacteria replaced with «more» harmful bacteria ✔

NOTE: Accept “affects/disturbs micro-ecosystems”.

Any one of:
«most are» toxic «to living organisms»
OR
incomplete combustion/incineration can produce toxic products/dioxins/phosgene
OR
carcinogenic/can cause cancer ✔
NOTE: Do not accept “harmful to the environment”.

accumulate in groundwater
OR
have limited biodegradability ✔
NOTE: Do not accept just “pollutes water”.

cost of disposal ✔
NOTE: Do not accept “hazard of disposal”.

NOTE: Accept “ozone depletion” only if there is some reference to chlorinated solvents.

Any two of:

HIV difficult to detect/remains dormant ✔

HIV mutates rapidly/quickly ✔

HIV replicates rapidly/quickly ✔

HIV destroys «T-»helper cells/white blood cells/lymphocytes
OR
HIV attacks immune system ✔

HIV has several «significantly different» strains/subtypes ✔

NOTE: Accept “virus” for “HIV”.
Do not accept “AIDS mutates” without mention of the HIV/virus.
Penalize the use of “AIDS” for “HIV” once only.
Accept “HIV metabolism linked to that of host cell” OR “drugs harm host cell as well as HIV”.

Unreacted salicylic acid may be present as an impurity in aspirin and can be detected in the infrared (IR) spectrum.

Name the functional group and identify the absorption band that diff erentiates salicylic acid from aspirin. Use section 26 of the data booklet.

Name:

Absorption band:

Deduce the protons responsible for signals X and Y by marking them on the structure of aspirin in (a). Use section 27 of the data booklet.

Identify the splitting pattern of signals X and Y.

X:

Y:

Name:
hydroxyl   [✔]

Absorption band:
3200–3600 «cm^–1»  [✔]

Note: Accept “phenol” OR “alcohol” but not “hydroxide”. 

correct X   [✔]
correct Y   [✔]

Note: X and Y must be near the Hs.

X: singlet AND Y: singlet  [✔]

Many candidates scored a mark for naming a functional group that differentiates salicylic acid from aspirin. Some incorrectly said ether or carboxylic acid. Many candidates also scored for identifying the absorption band although 1700-1750 was a popular incorrect answer.

There was considerable confusion with indicating protons responsible for ¹H NMR signals. Often entire functional groups were circled or carbon atoms and not hydrogen atoms were circled.

There was also great difficulty in identifying the splitting pattern of the signals. It was rare to see both signals identified as singlets.

Infrared (IR) spectroscopy is used to identify functional groups in organic compounds.

Deduce the wavenumber, in cm⁻¹, of an absorption peak found in the IR spectrum of testosterone but not in that of cholesterol.

Describe a technique for the detection of steroids in blood and urine.

Explain how redox chemistry is used to measure the ethanol concentration in a breathalyser.

1700−1750 «cm⁻¹» ✔
NOTE: Accept a specific wavenumber value within range.

Any three of:
sample/liquids vaporized «in oven/at high temperature»
OR
sample injected into mobile phase/inert gas
OR
nitrogen/helium/inert gas acts as mobile phase
OR
sample carried by inert gas «through column» ✔
NOTE: Award [1 max] for identifying suitable technique (eg GC-MS etc.).
Do not accept just “gas”.
Accept description of HPLC using liquid mobile phase.

stationary phase consists of a packed column
OR
packing/solid support acts as stationary phase ✔
NOTE: Accept named stationary phase, such as «long-chain» hydrocarbon/polysiloxane/silica.

components separated by partition «between mobile phase and stationary phase»
OR
gases/liquids/components have different retention times/R_f
OR
gases/liquids/components move through tube/column at different speeds/rates ✔

detector/mass spectrometer/MS «at end of column»
OR
databases/library of known fragmentation patterns can be used ✔
NOTE: Accept “area under peak proportional to quantity/amount/concentration of component present «in mixture»”.

ALTERNATIVE 1
oxidizing agent/«acidified» potassium dichromate(VI) converts ethanol to ethanoic acid ✔
colour change «from orange to green» is measured/analysed «using photocell» ✔

ALTERNATIVE 2
ethanol is oxidized to ethanoic acid «at anode and oxygen is reduced to water at cathode» ✔
current/voltage/potential is measured «by computer»
OR
current/voltage/potential is proportional to ethanol concentration ✔

NOTE: Accept names or formulas for reagents.
Accept “«acidified» dichromate/Cr₂O₇²⁻” for “K₂Cr₂O₇”.
Award [1 max] for "Cr(VI) going to Cr(III) AND colour changing/colour changing from orange to green".
Do not penalize incorrect oxidation state notation here.
Accept "EMF" for "voltage".

State an analytical technique used to separate anabolic steroids from other compounds in an athlete’s urine or blood.

Ethanol in breath can be detected by a redox reaction. Outline this method of detection. An equation is not required.

gas chromatography/GC

OR

high performance liquid chromatography/HPLC ✔ 

Accept “chromatography”, “TLC/thin-layer chromatography”, “paper chromatography” OR “extraction”.

Do not accept just “mass spectrometry/MS” but do not penalize any reference to MS with HPLC or GC (eg GC-MS).

ALTERNATIVE 1:

Any two of:

«blow through tube of» acidified «orange» potassium dichromate(VI)/K₂Cr₂O₇/dichromate/Cr₂O₇^2– ✔

Cr(VI)/Cr⁶⁺/Cr₂O₇^2– reduced to Cr(III)/Cr³⁺✔

colour changes «from orange» to green

OR

colour change is monitored ✔

ALTERNATIVE 2:

oxygen reduced to water

OR

ethanol oxidized to ethanoic/acetic acid ✔

current measured ✔

Accept “ethanol oxidized to ethanal/acetaldehyde”.

Outline two different ways in which antiviral medications work.

Any two of:

prevents virus attaching to host cell ✔

alters cell’s genetic material/DNA «so that virus cannot use it to multiply» ✔

blocks enzyme activity in the host cell «so that virus cannot use it to multiply» ✔

prevents removal of protein coat/capsid ✔

prevents injection of viral DNA/RNA into cell ✔

prevents release of «replicated» viruses from host cell ✔

Accept “prevents synthesis of virus by host cell”.

Accept “alters RNA/DNA/genetic material of virus”.

Do not accept just “mimics nucleotides”.

State two common side effects of radiotherapy.

Explain why technetium-99m is the most common radioisotope used in nuclear medicine.

25.0 μg of iodine-131, with a half-life of 8.00 days, was left to decay.

Calculate the mass of iodine-131, in μg, remaining after 32.0 days. Use section 1 of the data booklet.

Any two of:
hair loss
fatigue
nausea
sterility
skin reaction
diarrhoea
vomiting
damage to lymph system
urinary/bladder changes
anxiety/emotional problems
joint/muscular stiffness
loss of appetite
sore/dry mouth
loss of weight
secondary cancer ✔

Any two of:
half-life is 6 hours/long enough for a scan to occur
OR
half-life short enough not to remain in body ✔
NOTE: Accept “short half-life so patient is not exposed to lots of ionizing radiation”.

decay releases «low energy» gamma rays
OR
gamma rays less likely to be absorbed by cells ✔

can form several «coordination» complexes ✔
NOTE: Accept "can exist in many oxidation states «so can form multiple complexes»" OR "chemically versatile «so can act as a tracer by bonding to several bioactive compounds»”.

«low-energy» radiation/gamma-rays can be detected by common X-ray equipment ✔

ALTERNATIVE 1
4 half-lives ✔
1.56 «μg of iodine-131 remain» ✔

ALTERNATIVE 2
m = 25.0 ${\left(\frac{1}{2}\right)}^{\frac{32.0}{8.00}}$ ✔
1.56 «μg of iodine-131 remain» ✔

ALTERNATIVE 3
λ = « $\frac{\ln 2}{8.00}$ » = 8.66 × 10⁻² «day⁻¹» ✔
m = « $25.0{\text{e}}^{-8.66\times {10}^{-2}\times 32.0}=$ » 1.56 «μg of iodine-131 remain» ✔

Award [2] for correct final answer.

Describe how ionizing radiation destroys cancer cells.

Outline how Targeted Alpha Therapy (TAT) is used for treating cancers that have spread throughout the body.

Any two of:

radiation causes breaks in DNA chains

OR

radiation causes errors in DNA sequences

«damage accumulates and» cells cannot multiply

rapidly dividing/cancer cells more susceptible

Accept “alters DNA”.

[2 marks]

Any two of:

radiation source delivered directly to «targeted» cancer cells

by a carrier drug/protein/antibody

several sites in body can be targeted «at same time»

[2 marks]