Describe the function of chlorophyll in photosynthesis.

Compare and contrast the structures of starch and cellulose.

One similarity:

One difference:

Explain why maltose, C₁₂H₂₂O₁₁, is soluble in water.

absorbs/traps light «energy» ✔

initiates redox reactions
OR
transfers electrons ✔

One similarity:
1−4/glycosidic linkage
OR
glucose monomers/residues ✔

NOTE: Accept “both are polysaccharides”.

One difference:
starch has α-glucose AND cellulose has β-glucose «monomers»
OR
starch can form coiled/spiral/helical chains «and straight chains» AND cellulose cannot/can only form straight chains/can only form a linear structure
OR
starch «in amylopectin» also has 1−6 glycosidic links AND cellulose does not ✔

NOTE: Accept "cellulose has alternate glucose monomers upside down with respect to each other AND starch does not".

«solubility depends on forming many» H-bonds with water ✔
maltose has many hydroxyl/OH/oxygen atom/O «and forms many H-bonds» ✔

NOTE: Reference to “with water” required.
Accept “hydroxy” for “hydroxyl” but not “hydroxide/OH^–”.
Reference to many/several OH groups/O atoms required for M2.

Estimate the atom economy of this first step.

Suggest, giving one reason, whether this is an addition or condensation reaction.

Subsequent steps proceed under differing conditions, forming the dendrimer polymer with the following repeating unit.

State the name of one functional group in this repeating unit.

100%

Accept “almost 100%” if a catalyst is referred to.

[1 mark]

addition AND no atoms removed/all atoms accounted for/no loss of water/ammonia/inorganic by-product/small molecules
OR
addition AND there is only one «reaction» product

[1 mark]

amido
OR
amino

Accept “amide/carboxamide/carbamoyl” for “amido”.

Accept “amine“ for “amino”.

Accept “carbonyl”.

[1 mark]

Draw the structure of the dipeptide Asp–Phe using section 33 of the data booklet.

Describe, using another method, how a mixture of four amino acids, alanine, arginine, glutamic acid and glycine, could be separated when placed in a buffer solution of pH 6.0.

Suggest why alanine and glycine separate slightly at pH 6.5.

Calculate the ratio of [A⁻] : [HA] in a buffer of pH 6.0 given that pK_a for the acid is 4.83, using section 1 of the data booklet.

amide link (eg, CONH) ✔

correct order and structures of amino acids ✔

NOTE: Accept a skeletal formula or a full or condensed structural formula.
Accept zwitterion form of dipeptide.
Accept CO–NH but not CO–HN for amide link.

Any three of:
«gel» electrophoresis «technique»
OR
mixture «in buffer solution» placed on gel/paper ✔

voltage/potential «difference» applied ✔

amino acids move differently «depending on pH/isoelectric point» ✔

compare/measure distances travelled/R_f values ✔

NOTE: Accept “mixture placed on plate covered with polyacrylamide «gel» OR “mixture put in a gel «medium»”.

different sizes/molar masses/chain lengths «so move with different speeds» ✔

NOTE: Do not accept “different side-chains/R-groups/number of carbons”.

«6.0 = 4.83 + log $\frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$»

«log$\frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$= 1.17»

«[A⁻] : [HA] =» 14.8 : 1 ✔

NOTE: Accept “15:1”.
Do not accept 1:14.8.

The graph shows the change in oxygen partial pressure in blood, measured at different pH values.

Explain the effect of changing pH on the percentage saturation of hemoglobin at a given partial pressure of oxygen.

Explain the biomagnification of the pesticide DDT.

Vitamins are organic compounds essential in small amounts.

State the name of one functional group common to all three vitamins shown in section 35 of the data booklet.

as pH decreases, protons/CO₂ bind to allosteric sites
OR
as pH decreases, protons/CO₂ act as non-competitive inhibitor
OR
active/binding site changes shape ✔

saturation decreases
OR
more oxygen released
OR
affinity to oxygen decreases ✔

accumulates in fat/tissues/living organisms
OR
cannot be metabolized/does not break down «in living organisms»
OR
not excreted / excreted «very» slowly ✔

passes «unchanged» up the food chain
OR
increased concentration as one species feeds on another «up the food chain» ✔

NOTE: Accept “lipids” for “fat”.

hydroxyl ✔

NOTE: Accept “hydroxy” but not “hydroxide”.
Accept “alkenyl”.

Do not accept formula.

Calculate the energy released, in $\mathrm{kJ}$, from the complete combustion of $5.00 {\mathrm{dm}}^3$ of ethanol.

State a class of organic compounds found in gasoline.

Outline the advantages and disadvantages of using biodiesel instead of gasoline as fuel for a car. Exclude any discussion of cost.

A mixture of gasoline and ethanol is often used as a fuel. Suggest an advantage of such a mixture over the use of pure gasoline. Exclude any discussion of cost.

When combusted, all three fuels can release carbon dioxide, a greenhouse gas, as well as particulates. Contrast how carbon dioxide and particulates interact with sunlight.

Methane is another greenhouse gas. Contrast the reasons why methane and carbon dioxide are considered significant greenhouse gases.

Suggest a wavenumber absorbed by methane gas.

Determine the relative rate of effusion of methane ($M_{\mathrm{r}}=16.05$) to carbon dioxide ($M_{\mathrm{r}}=44.01$), under the same conditions of temperature and pressure. Use section 1 of the data booklet.

$«21 200 \mathrm{kJ} {\mathrm{dm}}^{-3}\times 5.00 {\mathrm{dm}}^3=»106000/1.06\times {10}^5«\mathrm{kJ}»$ ✔

alkane
OR
cycloalkane
OR
arene ✔

Accept “alkene”.
Do not accept just “hydrocarbon”, since given in stem.
Do not accept “benzene/aromatic” for “arene”.

Advantages: [2 max]

renewable ✔

uses up waste «such as used cooking oil» ✔

lower carbon footprint/carbon neutral ✔

higher flashpoint ✔

produces less ${\mathrm{SO}}_{\mathrm{x}}$/${\mathrm{SO}}_2$
OR
less polluting emissions ✔

has lubricating properties
OR
preserves/increases lifespan of engine ✔

increases the life of the catalytic converter ✔

eliminates dependence on foreign suppliers ✔

does not require pipelines/infrastructure «to produce» ✔

relatively less destruction of habitat compared to obtaining petrochemicals ✔

Accept “higher energy density” OR “biodegradable” for advantage.

Disadvantages: [2 max]

needs conversion/transesterification ✔

takes time to produce/grow plants ✔

takes up land
OR
deforestation ✔

fertilizers/pesticides/phosphates/nitrates «used in production of crops» have negative environmental effects ✔

biodiversity affected
OR
loss of habitats «due to energy crop plantations» ✔

cannot be used at low temperatures ✔

variable quality «in production» ✔

high viscosity/can clog/damage engines ✔

Accept “lower specific energy” as disadvantage.

Do not accept “lower octane number” as disadvantage”.

Any one:

uses up fossil fuels more slowly ✔

lower carbon footprint/CO2 emissions ✔

undergoes more complete combustion ✔

produces fewer particulates ✔

higher octane number/rating
OR
less knocking ✔

prevents fuel injection system build up
OR
helps keep engine clean ✔

Accept an example of a suitable advantage even if repeated from 11c.

carbon dioxide allows sunlight/short wavelength radiation to pass through AND particulates reflect/scatter/absorb sunlight ✔

Accept “particulates reflect/scatter/absorb sunlight AND carbon dioxide does not”.
Accept “$C{O}_{\mathit{2}}$ absorbs $IR$ «radiation» AND particulates reflect/scatter/absorb sunlight”.

Do not accept “traps” for “absorbs”.

carbon dioxide is highly/more abundant «in the atmosphere» ✔

methane is more effective/potent «as a greenhouse gas»
OR
methane/better/more effective at absorbing $\mathrm{IR}$ «radiation»
OR
methane has greater greenhouse factor
OR
methane has greater global warming potential/GWP✔

Accept “carbon dioxide contributes more to global warming” for M1.

any value or range within $2850–3090«{\mathrm{cm}}^{-1}»$ ✔

«rate of effusion of $\frac{{\mathrm{CH}}_4}{{\mathrm{CO}}_2}=\sqrt{\frac{44.01}{16.05}}=»1.656$ ✔

Almost all were able to calculate the energy released from the complete combustion of ethanol.

The majority cited correctly that alkanes are a class of organic compounds found in gasoline.

Most gained at least one mark for an advantage of using biodiesel instead of gasoline as fuel for a car and most scored one mark at least for a disadvantage of biodiesel. Many conveyed solid understanding, though the disadvantages were not as well articulated as the advantages. Some incorrectly based their responses on cost factors which were excluded as outlined in the stem of the question.

Most scored the one mark for this question, with "less knocking or higher octane number/rating" the most common correct answer seen.

The wording of this question was critical which involved contrasting how carbon dioxide and particulates interact with sunlight. Some missed the "Contrast" command term as the action verb. Loose, non-scientific syntax was often seen such as stating "traps" instead of "absorbs".

This was another "Contrast-type" question, which was better answered compared to (e)(i). Many scored both marks by stating that carbon dioxide is more abundant in the atmosphere whereas methane is more effective at absorbing IR radiation.

The main issue with this question was that a high percentage of candidates did not realise that wavenumber is the reciprocal of wavelength and hence wavenumber has typical units of cm^-1. Many incorrectly gave wavelength values, in nm, which did not answer the question posed.

The determination of the relative rate of effusion of methane to carbon dioxide was almost universally correctly computed as 1.656.

The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.

The chemical change in stored fats causes rancidity characterized by an unpleasant smell or taste.

Compare hydrolytic and oxidative rancidity.

State one similarity and one difference in composition between phospholipids and triglycerides.

Similarity:

Difference:

«one C=C bond»
«1 mole iodine : 1 mole oleic acid»

« $\frac{100\times 253.80}{282.46}$ =» 89.85 «g of I₂» ✔

NOTE: Accept “90 «g of I₂»”.

NOTE: Award [1] for any two sites or conditions from any of the four listed.
Accept “high temperature” for “heat”. Accept "lipase" for "enzyme".
Do not accept just “double bond”.
Accept “air” for “oxygen” and “UV/sun” for “light”.
Ignore any reference to heat/high temperature as a condition for oxidative.

Similarity:

«derived from» propane-1,2,3-triol/glycerol/glycerin/glycerine

OR
«derived from» at least two fatty acids
OR
contains ester linkages
OR
long carbon chains ✔

NOTE: Do not accept “two fatty acids as both a similarity and a difference”.
Do not accept just “hydrocarbon/carbon chains”.

Difference:

phospholipids contain two fatty acids «condensed onto glycerol» AND triglycerides three
OR
phospholipids contain phosphate/phosphato «group»/residue of phosphoric acid AND triglycerides do not ✔

NOTE: Accept “phospholipids contain phosphorus AND triglycerides do not".
Accept “phospholipids are amphiphilic AND triglycerides are not” OR “phospholipids have hydrophobic tails and hydrophilic heads AND triglycerides do not”.

Draw the structure of the monomers of Kevlar^® if the by-product of the condensation polymerization is hydrogen chloride.

State and explain why plasticizers are added to polymers.

Discuss why the recycling of plastics is an energy intensive process.

OR
H₂NC₆H₄NH₂ ✔

OR
Cl(O)CC₆H₄C(O)Cl ✔

increases flexibility/softness/plasticity ✔
break/weaken intermolecular forces/IMF/H-bonds «between chains» ✔

Any two of:
collection/transportation of plastic waste ✔

separation/sorting of different types «of plastic»
OR
separation/sorting of plastic from other materials ✔

melting plastic ✔

processing/washing/cleaning/drying/manufacture of recycled plastic ✔

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".

Deduce the repeating unit of the polymer and the other product of the reaction.

State the class of polymer to which PETE belongs.

Repeating unit:

Other product: water/H₂O

Continuation bonds necessary for the mark.

Accept alternative repeating unit with O at other end.

Do not penalize square brackets or n.

[2 marks]

condensation

Accept polyester or thermoplastic.

[1 mark]

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]