| Marks available | 2 |
| Reference code | 10M.3.sl.TZ1.C1 |
Question
Both carbon monoxide and hydrogen can be used to reduce iron ores. State the equations for the reduction of magnetite, Fe3O4, with
Explain why iron is obtained from its ores using chemical reducing agents but aluminium is obtained from its ores using electrolysis.
Both carbon monoxide and hydrogen can be used to reduce iron ores. State the equations for the reduction of magnetite, Fe3O4, with
(i) carbon monoxide.
(ii) hydrogen.
Explain why much of the iron produced in a blast furnace is converted into steel.
State the materials used for the positive and negative electrodes in the production of aluminium by electrolysis.
Positive electrode:
Negative electrode:
Markscheme
Al is more reactive than Fe / Al is higher than Fe in the reactivity series;
it is harder to reduce aluminium ores compared to iron ores / \({\text{F}}{{\text{e}}^{3 + }}\) is a better oxidizing agent than \({\text{A}}{{\text{l}}^{3 + }}\) / OWTTE;
(i) \({\text{F}}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}} + {\text{4CO}} \to {\text{3Fe}} + {\text{4C}}{{\text{O}}_{\text{2}}}\);
(ii) \({\text{F}}{{\text{e}}_3}{{\text{O}}_4} + {\text{4}}{{\text{H}}_2} \to {\text{3Fe}} + {\text{4}}{{\text{H}}_2}{\text{O}}\);
steel has more desirable (physical) characteristics than iron / steel is stronger than iron / OWTTE;
by adjusting the composition of steel it can be given specific properties / OWTTE;
Positive electrode
graphite/carbon;
Negative electrode
graphite/carbon (on a steel liner);
Examiners report
Part (a), which required candidates to explain the relative reactivity of iron and aluminium, proved challenging for most candidates.
Many candidates could correctly state the products of reduction of magnetite but several failed to balance the equations and thus lost marks.
Most candidates could explain the advantages of steel over iron in part (c).
Very few candidates could identify the electrodes used in the production of aluminium, but most could explain the importance of recycling aluminium in part (d).
| Marks available | 2 |
| Reference code | 16M.3.sl.TZ0.5 |
Question
Describe how the structures of ceramics differ from those of metals.
Markscheme
ceramics have «giant» ionic/covalent/ionic AND covalent structures
metals contain lattice of positive ions/cations in sea of delocalized electrons
Accept [1 max] for “ionic/covalent/ionic and covalent bonds in ceramics AND metallic bonds in metals”.
Accept suitable diagram for M2.
Examiners report
| Marks available | 1 |
| Reference code | 16N.3.sl.TZ0.3 |
Question
Materials science involves understanding the properties of materials and applying those properties to desired structures.
Magnesium oxide, MgO, and silicon carbide, SiC, are examples of ceramic materials. State the name of the predominant type of bonding in each material.
Predict the predominant type of bonding for a binary compound AB in which the electronegativity of both atoms is low. Use section 29 of the data booklet.
Markscheme
MgO: ionic AND SiC: covalent
Accept “covalent network/network covalent” for “covalent” but not just “network”.
metallic «bonding»
Examiners report
| Marks available | 2 |
| Reference code | 17M.3.sl.TZ1.6 |
Question
Lanthanum, La, and antimony, Sb, form compounds with bromine that have similar formulas, LaBr3 and SbBr3.
Determine the type of bond present in SbBr3, showing your method. Use sections 8 and 29 of the data booklet.
Lanthanum has a similar electronegativity to group 2 metals. Explain, in terms of bonding and structure, why crystalline lanthanum bromide is brittle.
Markscheme
polar covalent
average electronegativity «= \(\frac{1}{2}\)(3.0 + 2.0)» = 2.5 AND electronegativity difference «= 3.0 – 2.0» = 1.0
[2 marks]
ionic bonding
OR
electrostatic forces between ions
«slight» movement brings ions of same charge adjacent to each other «causing the crystal to break»
OR
«slight» movement results in repulsion between layers «causing the crystal to break»
[2 marks]
Examiners report
| Marks available | 2 |
| Reference code | 17M.3.sl.TZ2.3 |
Question
Polymer nanocomposites often have better structural performance than conventional materials. Lithographic etching and metal coordination are two methods of assembling these nanocomposites.
Nanoparticles anchor plasticizers in PVC so that they cannot escape from the polymer as easily.
State the two distinct phases of a composite.
Identify the methods of assembling nanocomposites by completing the table.
Explain how the structure of plasticizers enables them to soften PVC.
Suggest a reason why nanoparticles can better anchor plasticizers in the polymer.
Markscheme
reinforcing «phase»
«embedded in» matrix «phase»
[2 marks]
Award [2] for all 4, [1] for 2 or 3 correct.
[2 marks]
Any three of:
contain a polar group «which locks into the polymer»
a non-polar group «which weakens the forces between chains»
embedded between chains of polymers
«plasticizer molecules» fit between chains
«plasticizer molecules» prevent chains from forming crystalline regions
«plasticizer molecules» keeps strands/chains/molecules separated
«plasticizer molecules» increase space/volume between chains
weakens intermolecular/dipole-dipole/London/dispersion/instantaneous induced dipole-induced dipole/van der Waals/vdW forces
Do not accept “«plasticizer molecules» “lower density” or “softer”.
[3 marks]
more places «for plasticizers» to bond
OR
increased surface area
[1 mark]
Examiners report
| Marks available | 1 |
| Reference code | 17N.3.sl.TZ0.4 |
Question
It is wise to fill dental cavities before irreversible tooth decay sets in. An amalgam (alloy of mercury, silver, and other metals) is often used although many prefer a white composite material.
Outline the composition of an alloy and a composite.
Outline why an alloy is usually harder than its components by referring to its structure.
At present, composite fillings are more expensive than amalgam fillings.
Suggest why a patient might choose a composite filling.
Explain how Inductively Coupled Plasma (ICP) Spectroscopy could be used to determine the concentration of mercury in a sample of dental filling.
Markscheme
Alloy:
mixture of metal with other metals/non-metals
OR
mixture of elements that retains the properties of a metal
Composite:
reinforcing phase embedded in matrix phase
Award [1 max] for implying “composites only have heterogeneous/nonhomogeneous compositions”.
[Max 2 Marks]
difference in ionic/atomic radius prevents layers sliding over each other
Accept “difference in diameter/packing of cations prevents layers sliding over each other”.
concern about Hg poisoning
OR
«composite» is white «so looks more like tooth»
OR
galvanic response potential exists
OR
local allergic potential
OR
less damage/destruction of healthy tooth tissue
OR
long term corrosion requires replacement
OR
gradual darkening of tooth
Accept other correct responses.
Any three of:
sample injected into argon «plasma»
atoms «of sample» are excited/ionised
OR
electrons are promoted
electrons drop back/recombine with ions AND emit photons of characteristic energies/wavelengths/frequencies
total number of photons is proportional to concentration of element
actual concentration found from calibration/standard curve
Accept “graph/plot” for “curve”.
[Max 3 Marks]
Examiners report
| Marks available | 1 |
| Reference code | 18M.3.sl.TZ1.3 |
Question
Aluminium and high density polyethene (HDPE) are both materials readily found in the kitchen, for example as saucepans and mixing bowls respectively. In these applications it is important that they are impermeable to water.
Both materials are also used in other applications that are more demanding of their physical properties. Carbon nanotubes are often incorporated into their structures to improve certain properties.
Discuss, in terms of its structure, why an aluminium saucepan is impermeable to water.
State the name given to a material composed of two distinct solid phases.
State one physical property of HDPE that will be affected by the incorporation of carbon nanotubes.
Describe how carbon nanotubes are produced by chemical vapour deposition (CVD).
State the property of carbon nanotubes that enables them to form a nematic liquid crystal phase.
Markscheme
«close packed» lattice of metal atoms/ions
no spaces for water molecules to pass though the structure
[2 marks]
composite
[1 mark]
melting point
OR
permeability
OR
density
OR
conductivity
OR
elasticity/stiffness
OR
brittleness/flexibility
OR
«tensile» strength
Accept “colour/transparency”.
[1 mark]
Any three of:
hydrocarbon/carbon-containing gas/compound
mixed with inert gas
heat/high temperature
«transition» metal catalyst
hydrocarbon/carbon compound decomposes to form carbon «nanotubes»
nanotubes form on catalyst surface
Accept “ethanol” or specific hydrocarbons.
Accept “N2”, “H2”, “NH3” or specific inert gases.
Accept temperature or range within 600–800 °C.
Accept specific metals such as Ni, Co or Fe.
[3 marks]
rod shaped molecules
[1 mark]
Examiners report
| Marks available | 1 |
| Reference code | 18M.3.sl.TZ1.4 |
Question
Both HDPE (high density polyethene) and LDPE (low density polyethene) are produced by the polymerization of ethene.
Both of these are thermoplastic polymers. Outline what this term means.
Compare and contrast the structures of HDPE and LDPE.
State one way in which a physical property of HDPE, other than density, differs from that of LDPE as a result of this structural difference.
The production of HDPE involves the use of homogeneous catalysts. Outline how homogeneous catalysts reduce the activation energy of reactions.
Trace amounts of metal from the catalysts used in the production of HDPE sometimes remain in the product. State a technique that could be used to measure the concentration of the metal.
Suggest two of the major obstacles, other than collection and economic factors, which have to be overcome in plastic recycling.
Suggest why there are so many different ways in which plastics can be classified. HDPE can, for example, be categorized thermoplastic, an addition polymer, having Resin Identification Code (RIC) 2, etc.
Markscheme
soften/melt when heated
OR
can be melted and moulded
Accept “low melting point” OR “can be moulded when heated”.
[1 mark]
both have «long» hydrocarbon chains
OR
both have chains comprising CH2 units
HDPE has little/no branching AND LDPE has «more» branching
Accept “CH2–CH2 units”.
Accept “HDPE more crystalline”.
[2 marks]
HDPE is more rigid/less flexible
OR
HDPE has a higher melting point
OR
HDPE has greater «tensile» strength
Accept “HDPE has lower ductility”.
[1 mark]
form «temporary» activated complexes/reaction intermediates
Accept “consumed in one reaction/step AND regenerated in a later reaction/step”.
Accept “provides alternative mechanism”.
[1 mark]
inductively coupled plasma/ICP spectroscopy using mass spectroscopy/mass spectrometry/MS/ICP-MS
OR
inductively coupled plasma/ICP spectroscopy using optical emission spectroscopy/OES/ICP-OES
Accept “atomic absorption/aa spectroscopy” or “MS/massspectroscopy/mass spectrometry”.
[1 mark]
Any two of:
many types «of plastics» exist
OR
«plastics» require sorting «by type»
«plastics» need to be separated from non-plastic materials
OR
«often» composites/moulded on/bound to non-plastic/other components
Accept other valid factors such as thermal decomposition of some plastics, production of toxic fumes, etc.
[2 marks]
«different classifications are appropriate for» different properties/applications/purposes
[1 mark]
Examiners report
| Marks available | 2 |
| Reference code | 18M.3.sl.TZ2.3 |
Question
Inductively Coupled Plasma (ICP) used with Mass Spectrometry (MS) or Optical Emission Spectrometry (OES) can be used to identify and quantify elements in a sample.
The following graphs represent data collected by ICP-OES on trace amounts of vanadium in oil.
Graph 1: Calibration graph and signal for 10 μg kg−1 of vanadium in oil
Graph 2: Calibration of vanadium in μg kg−1
[Source: © Agilent Technologies, Inc.1998. Reproduced with Permission, Courtesy of Agilent Technologies, Inc.]
ICP-OES/MS can be used to analyse alloys and composites. Distinguish between alloys and composites.
ICP-MS is a reference mode for analysis. The following correlation graphs between ICP-OES and ICP-MS were produced for yttrium and nickel.
Each y-axis shows concentrations calculated by ICP-OES; each x-axis shows concentrations for the same sample as found by ICP-MS.
The line in each graph is y = x.
Discuss the effectiveness of ICP-OES for yttrium and nickel.
Identify the purpose of each graph.
Calculate, to four significant figures, the concentration, in μg kg−1, of vanadium in oil giving a signal intensity of 14 950.
Vanadium(V) oxide is used as the catalyst in the conversion of sulfur dioxide to sulfur trioxide.
SO2(g) + V2O5(s) → SO3(g) + 2VO2(s)
\(\frac{1}{2}\)O2(g) + 2VO2(s) → V2O5(s)
Outline how vanadium(V) oxide acts as a catalyst.
Markscheme
Alloy:
mixture of metal with other metals/non-metals
OR
mixture of elements that retains the properties of a metal
Composite:
reinforcing phase embedded in matrix phase
Award [1 max] for implying “composites only have heterogeneous/nonhomogeneous compositions”.
[2 marks]
effective for yttrium «but less/not for nickel»
points on nickel graph do not lie on «y = x» line
OR
cannot be used for low concentrations of nickel
OR
concentration of nickel is lower than recorded value
Accept “ICP-OES is more accurate for lower yttrium concentrations than higher concentrations” for M1.
Accept [Ni] and [Y] for concentrations of nickel and yttrium.
Accept “detection limit for yttrium is lower than for nickel” for M2.
Award [1 max] for “more accurate for yttrium at lower concentrations AND nickel at higher concentrations”.
[2 marks]
Graph 1: determines wavelength of maximum absorption/maximum intensity «for vanadium»
Graph 2: determines absorption of known concentrations «at that wavelength»
OR
estimates [V]/concentration in a sample using «the signal» intensity
Do not accept just “determines maximum wavelength/λmax” for M1.
Do not accept “calibration curve” for M2.
[2 marks]
«14 950 = 392.19x + 147.62»
x = 37.74 «μg kg–1»
Answer must be given to four significant figures.
Do not accept values obtained directly from the graph.
[1 mark]
vanadium reduced in first reaction AND oxidized in second reaction
OR
V2O5 oxidizes SO2 in first reaction AND VO2 reduces O2 in second reaction
OR
vanadium returns to original oxidation state «after reaction»
provides an alternative reaction pathway/mechanism «with a lower activation energy» ✔
Do not accept “reactants adsorb onto surface AND products desorb”.
Accept “oxidation number” for “oxidation state”.
[2 marks]
Examiners report
| Marks available | 1 |
| Reference code | 18M.3.sl.TZ2.4 |
Question
Propene can polymerize to form polypropene.
Propene monomer: 
Sketch four repeating units of the polymer to show atactic and isotactic polypropene.
State the chemical reason why plastics do not degrade easily.
Compare two ways in which recycling differs from reusing plastics.
Civilizations are often characterized by the materials they use.
Suggest an advantage polymers have over materials from the iron age.
Markscheme
Do not accept syndiotactic (alternating orientation of the CH3 groups), eg,
for M1 or M2.
Accept any correct atactic ordering of CH3 groups.
Penalize missing hydrogens or incorrect bond connectivities once only.
Accept skeletal structures.
Ignore continuation bonds, brackets and “n” indices in structures.
[2 marks]
strong covalent bonds
Accept “moisture cannot get inside the plastic matrix, and bacteria cannot live without moisture, so they cannot attack the polymer chains”.
Accept “bacteria lack the enzymes required to break down the hydrocarbon chains”.
[1 mark]
Any two of:
Recycling: shredded/melted/reformed AND Reuse: used in its current form
recycling is more energy intensive «than reusing»
recycling degrades the quality of plastic but reusing «typically» does not
recycling breaks down original product to form a new product whereas reuse extends product life
[2 marks]
more pliable/flexible materials
OR
more durable/non-corrosive/longer-lasting materials
OR
greater variety of materials
OR
lower density
OR
can be clear/translucent
Accept “more adaptable”.
Do not accept just “more useful”.
[1 mark]