SL Paper 3
Infrared (IR) spectroscopy is often used for the identification of polymers, such as PETE, for recycling.
LDPE and high density polyethene (HDPE) have very similar IR spectra even though they have rather different structures and physical properties.
Below are the IR spectra of two plastics (A and B); one is PETE, the other is low density polyethene (LDPE).
Deduce, giving your reasons, the identity and resin identification code (RIC) of A and B using sections 26 and 30 of the data booklet.
Describe the difference in their structures.
Explain why the difference in their structures affects their melting points.
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.
Explain the biomagnification of the pesticide DDT.
Explain why maltose, C12H22O11, is soluble in water.
Carbohydrates are energy-rich molecules which can be synthesized in some plant cells from inorganic compounds.
State the raw materials and source of energy used in the process described above.
The structures of two molecules, X and Y, are shown below.
(i) Justify why both these molecules are carbohydrates.
(ii) Distinguish between these molecules in terms of their functional groups.
Amylose is an unbranched polysaccharide composed of repeating units of glucose.
(i) Draw the structure of the repeating unit of amylose. Use section 34 of the data booklet.
(ii) Amylose is a major component of starch. Corn starch can be used to make replacements for plastics derived from oil, especially for packaging. Discuss one potential advantage and one disadvantage of this use of starch.
Monosaccharides can combine to form disaccharides and polysaccharides.
Identify the functional groups which are present in only one structure of glucose.
Sucrose is a disaccharide formed from -glucose and β-fructose.
Deduce the structural formula of sucrose.
Starch is a constituent of many plastics. Suggest one reason for including starch in plastics.
Suggest one of the challenges scientists face when scaling up the synthesis of a new compound.
Oseltamivir (Tamiflu) and zanamivir (Relenza) are both used as antivirals to help prevent the spread of the flu virus, but are administered by different methods.
Zanamivir must be taken by inhalation, not orally. Deduce what this suggests about the bioavailability of zanamivir if taken orally.
Oseltamivir does not possess the carboxyl group needed for activity until it is chemically changed in the body. Deduce the name of the functional group in oseltamivir which changes into a carboxyl group in the body. Use section 37 of the data booklet.
The synthesis of oseltamivir is dependent on a supply of the precursor shikimic acid, which is available only in low yield from certain plants, notably Chinese star anise. State one alternative green chemistry source of shikimic acid.
Vegetable oils, such as that shown, require conversion to biodiesel for use in current internal combustion engines.
State two reagents required to convert vegetable oil to biodiesel.
Deduce the formula of the biodiesel formed when the vegetable oil shown is reacted with the reagents in (a).
Explain, in terms of the molecular structure, the critical difference in properties that makes biodiesel a more suitable liquid fuel than vegetable oil.
Determine the specific energy, in kJg−1, and energy density, in kJcm−3, of a particular biodiesel using the following data and section 1 of the data booklet.
Density = 0.850 gcm−3; Molar mass = 299 gmol−1;
Enthalpy of combustion = 12.0 MJmol−1.
Amino acids are usually identified by their common names. Use section 33 of the data booklet.
State the IUPAC name for leucine.
A mixture of amino acids is separated by gel electrophoresis at pH 6.0. The amino acids are then stained with ninhydrin.
(i) On the diagram below draw the relative positions of the following amino acids at the end of the process: Val, Asp, Lys and Thr.
(ii) Suggest why glycine and isoleucine separate slightly at pH 6.5.
Determine the number of different tripeptides that can be made from twenty different amino acids.
The fibrous protein keratin has a secondary structure with a helical arrangement.
(i) State the type of interaction responsible for holding the protein in this arrangement.
(ii) Identify the functional groups responsible for these interactions.
Aspartame is formed from the two amino acids aspartic acid (Asp) and phenylalanine (Phe).
Draw the structure of the dipeptide Asp–Phe using section 33 of the data booklet.
The isoelectric point of amino acids is the intermediate pH at which an amino acid is electrically neutral.
Suggest why Asp and Phe have different isoelectric points.
Ethanol is a biofuel that can be mixed with gasoline.
Write the equation for the complete combustion of ethanol.
Outline the evidence that relates global warming to increasing concentrations of greenhouse gases in the atmosphere.
Explain, including a suitable equation, why biofuels are considered to be carbon neutral.
State the type of reaction that occurs when ethanol reacts with vegetable oil to form biodiesel.
Octane number is a measure of the performance of engine fuel.
Suggest why a high-octane number fuel is preferable.
Reforming reactions are used to increase the octane number of a hydrocarbon fuel.
Suggest the structural formulas of two possible products of the reforming reaction of heptane, C7H16.
The 1H NMR spectrum of one of the products has four signals. The integration trace shows a ratio of the areas under the signals of 9 : 3 : 2 : 2.
Deduce the structural formula of the product.
Gasoline (petrol), biodiesel and ethanol are fuels.
[U.S. Department of Energy. https://afdc.energy.gov/]
Calculate the energy released, in , from the complete combustion of 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.
Contrast the molecular structures of biodiesel and the vegetable oil from which it is formed.
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.
Codeine, morphine and diamorphine (heroin) are derived from opium.
State the names of two functional groups present in all three molecules, using section 37 of the data booklet.
Explain why diamorphine has greater potency than morphine.
Organic molecules can be visualized using three-dimensional models built from kits such as that pictured below.
Describe two differences, other than the number of atoms, between the models of ethane and ethene constructed from the kit shown.
The above ball and stick model is a substituted pyridine molecule (made of carbon, hydrogen, nitrogen, bromine and chlorine atoms). All atoms are shown and represented according to their relative atomic size.
Label each ball in the diagram, excluding hydrogens, as a carbon, C, nitrogen, N, bromine, Br, or chlorine, Cl.
Suggest one advantage of using a computer generated molecular model compared to a ball and stick 3-D model.
Pyridine, like benzene, is an aromatic compound.
Outline what is meant by an aromatic compound.
Stearic acid (Mr = 284.47) and oleic acid (Mr = 282.46) have the same number of carbon atoms. The structures of both lipids are shown in section 34 of the data booklet.
The iodine number is the number of grams of iodine which reacts with 100 g of fat. Calculate the iodine number of oleic acid.
State one impact on health of the increase in LDL cholesterol concentration in blood.
Explain why stearic acid has a higher melting point than oleic acid.
State one similarity and one difference in composition between phospholipids and triglycerides.
Similarity:
Difference:
Identify a reagent that hydrolyses triglycerides.
In a class experiment, students were asked to determine the value of x in the formula of a hydrated salt, BaCl2･xH2O. They followed these instructions:
- Measure the mass of an empty crucible and lid.
- Add approximately 2 g sample of hydrated barium chloride to the crucible and record the mass.
- Heat the crucible using a Bunsen burner for five minutes, holding the lid at an angle so gas can escape.
- After cooling, reweigh the crucible, lid and contents.
- Repeat steps 3 and 4.
Their results in three trials were as follows:
State and explain the further work students need to carry out in trial 2 before they can process the results alongside trial 1.
In trial 3, the students noticed that after heating, the crucible had turned black on the outside. Suggest what may have caused this, and how this might affect the calculated value for x in the hydrated salt.
List two assumptions made in this experiment.
Consider the structures of medicinal molecules in section 37 of the data booklet.
Name two functional groups that both zanamivir and oseltamivir contain.
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.
Consider the following lipid and carbohydrate.
In order to determine the number of carbon-carbon double bonds in a molecule of linoleic acid, 1.24 g of the lipid were dissolved in 10.0 cm3 of non-polar solvent.
The solution was titrated with a 0.300 mol dm–3 solution of iodine, I2.
Determine the empirical formula of linoleic acid.
The empirical formula of fructose is CH2O. Suggest why linoleic acid releases more energy per gram than fructose.
State the type of reaction occurring during the titration.
Calculate the volume of iodine solution used to reach the end-point.
Outline the importance of linoleic acid for human health.
Liquid-crystal displays (LCDs) have many uses.
A molecule which acts as a thermotropic liquid crystal is shown.
State the name of the functional group which allows the molecule to be responsive to applied electric fields.
Explain the effects of very low and high temperatures on the liquid-crystal behaviour of this molecule.
Low temperature:
High temperature:
Methadone, a synthetic opioid, binds to opioid receptors in the brain.
Compare and contrast the functional groups present in methadone and diamorphine (heroin), giving their names. Use section 37 of the data booklet.
Methadone is sometimes used to help reduce withdrawal symptoms in the treatment of heroin addiction. Outline one withdrawal symptom that an addict may experience.