(i) The diagram below shows the diffraction of two X-ray beams, y and z of wavelength λ, shining on a chromium crystal whose planes are a distance d nm apart.

Deduce the extra distance travelled by the second beam, z, compared to the first one, y.

(ii) State the Bragg’s condition for the observed diffraction to be at its strongest (constructive interference).

(i) The mass of one unit cell of chromium metal is 17.28 × 10⁻²³ g. Calculate the number of unit cells in one mole of chromium. A_r(Cr) = 52.00.

(ii) Deduce the number of atoms of chromium per unit cell.

Compare and contrast the Fenton and Haber–Weiss reaction mechanisms.

Adsorption and chelation are two methods of removing heavy metal ion pollution from the environment.

(i) Describe the process of adsorption.

(ii) Deduce the structure of the complex ion formed by the reaction of three H₂N−CH₂−CH₂−NH₂ chelating molecules with a mercury(II) ion.

Describe the Meissner effect.

Outline one difference between type 1 and type 2 superconductors.

Fermentation of sugars from corn starch produces propane-1,3-diol, which can be polymerized with benzene-1,4-dicarboxylic acid to produce the PTT polymer (polytrimethylene terephthalate).

(i) Draw the molecular structure of each monomer.

(ii) Deduce the name of the linkage formed on polymerization between the two monomers and the name of the inorganic product.

Precipitation is one method used to treat waste water.

Phosphates, ${\mathrm{PO}}_4^{3-}$, in waste water can be removed by precipitation with magnesium ions. $K_{sp}$ of magnesium phosphate is $1.04\times {10}^{-24}$.

$3{\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right)+2{{\mathrm{PO}}_4}^{3-}\left(\mathrm{aq}\right)\to {\mathrm{Mg}}_3\left({\mathrm{PO}}_4{)}_2\right(\mathrm{s})$

Calculate the maximum solubility of phosphate ions in a solution containing $0.0100 \mathrm{mol} {\mathrm{dm}}^{-3}$ magnesium ions.

Precipitation is one method used to treat waste water.

Zinc, cadmium, nickel, and lead are metal ions which can be removed by precipitation. Explain why waste water is adjusted to a pH of 9−10 to remove these ions by referring to section 32 of the data booklet.

Explain these properties of carbon nanotubes.

CNT can act as Type 2 superconductors. Outline why Type 2 superconductors are generally more useful than Type 1.

Explain the role of electrons in superconducting materials in terms of the Bardeen–Cooper–Schrieffer (BCS) theory.

Alloying metals changes their properties. Suggest one property of magnesium that could be improved by making a magnesium–CNT alloy.

Pure magnesium needed for making alloys can be obtained by electrolysis of molten magnesium chloride.

© International Baccalaureate Organization 2020

Calculate the theoretical mass of magnesium obtained if a current of 3.00 A is used for $10.0$ hours. Use charge :(Q) = current (I) × time (t)  and section 2 of the data booklet.

Suggest a gas which should be continuously passed over the molten magnesium in the electrolytic cell.

Zeolites can be used as catalysts in the manufacture of CNT. Explain, with reference to their structure, the high selectivity of zeolites.

Experiments have been done to explore the nematic liquid crystal behaviour of CNT. Justify how CNT molecules could be classified as nematic.

Outline the two distinct phases of this composite.

Thermoplastic composites are increasingly replacing thermosets.

Suggest one advantage of thermoplastic polymers over thermosets.

Explain how thermoplastics, such as polyvinylchloride, PVC, can be made more flexible by the addition of phthalate ester plasticizers.

Explain why phthalates are replaced by other plasticizers in the production of plastics.

Classify PVC and polyethene terephthalate, PET, as addition or condensation polymers and deduce the structural formulas.

Identify the type of bonding in lithium hydride, using sections 8 and 29 of the data booklet.

Identify the colour of the emission spectrum of lithium using section 17 of the data booklet.

Suggest why ICP-OES does not give good quantitative results for distinguishing ⁶Li from naturally occurring lithium.

Suggest a better method.

Lithium is obtained by electrolysis of molten lithium chloride. Calculate the time, in seconds, taken to deposit 0.694 g Li using a current of 2.00 A.

Q (charge) = I (current) × t (time)

Lithium has shown some superconductive properties when doped into graphene or when under high pressure. Under high pressure, however, the Meissner effect is absent.

Describe the Meissner effect.

At very low temperatures, lithium atoms enhance the phonon binding of electrons in graphene suggesting the formation of Cooper pairs.

Explain how Cooper pairs are formed.

Lithium forms a crystalline lattice with the unit cell structure shown below.

X-ray diffraction shows that the length of the edge of the unit cell is 3.51 × 10⁻⁸ cm.

Determine the density of lithium, in g cm⁻³, using sections 2 and 6 of the data booklet.

Outline the nature of the plasma state and how it is produced in ICP-MS.

Hydrogen sulfide could be used to remove antimony(III) ions from a solution.

Determine the concentration of antimony(III) ions that would be required to precipitate antimony(III) sulfide in a solution saturated with hydrogen sulfide.

[S²⁻] in water saturated with hydrogen sulfide = 1.0 × 10⁻¹⁴ mol dm⁻³ 

K_sp (Sb₂S₃) = 1.6 × 10⁻⁹³

Identify a ligand that could be used to chelate antimony(III) ions in solution.

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

State the class of polymer to which PETE belongs.

Lanthanum has a hexagonal close packed (hcp) crystal structure. State the coordination number of each lanthanum atom.

Lanthanum becomes superconducting below 5 K. Explain, in terms of Bardeen–Cooper–Schrieffer (BCS) theory, how superconductivity occurs.

Outline why superconductivity only occurs at low temperatures.

Identify the other product formed.

Explain why EDTA, a chelating agent, is more effective in removing heavy metal ions from solution than monodentate ligands.

Label with an asterisk, *, the chiral carbon atom.

Explain the effects of very low and high temperatures on the liquid-crystal behaviour of this molecule.

Low temperature:

High temperature:

Calculate the total number of cobalt atoms within its unit cell.

The atomic radius, r, of cobalt is 1.18 × 10^–8 cm. Determine the edge length, in cm, of the unit cell, a, using the second diagram.

Determine a value for the density of cobalt, in g cm^–3, using data from sections 2 and 6 of the data booklet and your answers from (a) and (b) (i).

If you did not obtain an answer to (b) (i), use 3.00 × 10^–8 cm but this is not the correct answer.

Describe how the monomers of addition polymers and of condensation polymers differ.

Identify the type of intermolecular bonding that is responsible for Kevlar^®’s strength.

The diagram illustrates the crystal structure of aluminium metal with the unit cell indicated. Outline the significance of the unit cell.

When X-rays of wavelength 0.154 nm are directed at a crystal of aluminium, the first order diffraction pattern is observed at 18°. Determine the separation of layers of aluminium atoms in the crystal, in m, using section 1 of the data booklet.

Deduce what the shape of the graph indicates about aluminium.

Outline why the resistance of aluminium increases above 1.2 K.

The concentration of aluminium in drinking water can be reduced by precipitating aluminium hydroxide. Calculate the maximum concentration of aluminium ions in water of pH 7 at 298 K. Solubility product of aluminium hydroxide = 3.3 × 10⁻³⁴ at 298 K.

State the name of one method, other than precipitation, of removing heavy metal ions from solution in water.

The solubility product, K_sp , of cadmium sulfide, CdS, is 8.0 × 10^–27. Determine the concentration of cadmium ions in 1.0 dm³ of a saturated solution of cadmium sulfide to which 0.10 mol of solid sodium sulfide has been added, stating any assumption you make.

Nickel(II) ions are least soluble at pH 10.5. Calculate the molar solubility of nickel(II) hydroxide at this pH. K_spNi(OH)₂ = 5.48 × 10^–16.

Rhodium is paramagnetic with an electron configuration of [Kr] 5s¹4d⁸.

Explain, in terms of electron spin pairing, why paramagnetic substances are attracted to a magnetic field and diamagnetic substances are not.

Rhodium is a type 1 superconductor.

Sketch graphs of resistance against temperature for a conductor and superconductor.

Contrast type 1 and type 2 superconductors by referring to three differences between them.

Deduce the number of atoms per unit cell in vanadium.

Calculate the expected first order diffraction pattern angle, in degrees, if x-rays of wavelength 150 pm are directed at a crystal of vanadium. Assume the edge length of the crystal to be the same as separation of layers of vanadium atoms found by x-ray diffraction. Use section 1 of the data booklet.

Calculate the average mass, in g, of a vanadium atom by using sections 2 and 6 of the data booklet.

Determine the volume, in cm³, of a vanadium unit cell.

Determine the density, in g cm⁻³, of vanadium by using your answers to (a)(i), (a)(iii) and (a)(iv).

Vanadium and other transition metals can interfere with cell metabolism.

State and explain one process, other than by creating free radicals, by which transition metals interfere with cell metabolism.

Vanadium(IV) ions can create free radicals by a Fenton reaction.

Deduce the equation for the reaction of V⁴⁺ with hydrogen peroxide.

Distinguish between the manufacture of polyester and polyethene.

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.

State the type of particle present in the plasma formed.

Calculate the concentration of lead ions in the sample in mol dm^‒3.

Lead ions are toxic and can be precipitated using hydroxide ions.

Pb²⁺ (aq) + 2OH^‒ (aq) $\rightleftharpoons$ Pb(OH)₂ (s)

Sufficient sodium hydroxide solid is added to the antacid sample to produce a 1.0 × 10^‒2 mol dm^‒3 hydroxide ion solution at 298 K.

Deduce if a precipitate will be formed, using section 32 of the data booklet.

If you did not calculate the concentration of lead ions in (b)(i), use the value of 2.4 × 10⁻⁴ mol dm^‒3, but this is not the correct value.

Electrolysis is used to obtain lead from Pb²⁺ (aq) solution.

Determine the time, in hours, required to produce 0.0500 mol lead using a current (I) of 1.34 A. Use section 2 of the data booklet and the equation, charge (Q) = current (I) × time (t, in seconds).

State one feature of a chelating agent.

An aqueous lead(II) ion reacts with three ethane-1,2-diamine molecules to form an octahedral chelate ion.

Outline why the chelate ion is more stable than the reactants.

Outline why this type of classification is not entirely satisfactory by using magnesium diboride, MgB₂, as an example. Refer to sections 8 and 29 of the data booklet.

Structures of poly(methyl acrylate), PMA, and Bakelite^® are shown.

Suggest, giving reasons, which is the thermoplastic polymer and which is the thermosetting polymer.

A zeolite is an alternative catalyst for this reaction.

Explain how zeolites act as selective catalysts.

State the names of the two terminal functional groups in X.

Deduce the repeating unit of the polymer of X.

Repeating units of several polymers are listed.

The infrared (IR) spectrum of one of these polymers is shown.

Deduce, giving a reason, the name of this polymer and its Resin Identification Code (RIC), using sections 26 and 30 in the data booklet.

State the name of the crystal structure of gold.

Calculate the number of atoms per unit cell of gold, showing your working.

The edge length of the gold unit cell is 4.08 × 10^‒8 cm.

Determine the density of gold in g cm^‒3, using sections 2 and 6 of the data booklet.

Describe the structure and bonding of a carbon nanotube.

Structure:

Bonding:

Suggest one application for carbon nanotubes.

X-ray crystallography of a metal crystal produces a diffraction pattern of bright spots.

Using X-rays of wavelength 1.54 × 10⁻¹⁰ m, the first bright spots were produced at an angle θ of 22.3° from the centre.

Calculate the separation between planes of atoms in the lattice, in meters, using section 1 of the data booklet.

Outline two differences between heterogeneous and homogeneous catalysts.

Suggest, giving a reason, how elastomers used for the tyre tread can increase the traction between the tyre and the road.

Tyre fires emit trace quantities of polychlorinated dibenzofurans and polychlorinated dibenzo-p-dioxin.

Outline, using section 31 of the data booklet, why polychlorinated dibenzofuran is not classed chemically as a dioxin but considered “dioxin-like”.

Classify polybutadiene as either an addition or condensation polymer, giving a reason.

State one factor considered when making green chemistry polymers.

Determine the mass of aluminium, in g, that could be extracted from an appropriate solution by a charge of 48 250 C. Use sections 2 and 6 of the data booklet.

Once extracted, the purity of the metal can be assessed using ICP-MS. Suggest two advantages of using plasma technology rather than regular mass spectrometry.

Explain the action of metals as heterogeneous catalysts.

Outline how alloys conduct electricity and why they are often harder than pure metals.

Conduct electricity:

Harder than pure metals:

Carbon nanotubes are added to metals to increase tensile strength.

Write an equation for the formation of carbon nanotubes from carbon monoxide.

Describe the characteristics of the nematic liquid crystal phase.

Shape of molecules:

Distribution: 

State what is meant by a superconductor.

Outline the difference in behaviour of Type 1 and Type 2 superconductors when the temperature is lowered.

Outline why heavy metals are toxic.

Determine the maximum concentration of lead(II) ions at 298 K in a solution in which the concentration of carbonate ions is maintained at 1.10 × 10⁻⁴ mol dm⁻³. Use section 32 of the data booklet.

State a method, other than precipitation, of removing heavy metal ions from solution.

Draw a section of isotactic polychloroethene (polyvinylchloride, PVC) showing all the atoms and all the bonds of four monomer units.

The infrared (IR) spectrum of polyethene is given.

Suggest how the IR spectrum of polychloroethene would diff er, using section 26 of the data booklet.

Explain how plasticizers affect the properties of plastics.

Suggest why the addition of plasticizers is controversial.

Outline, giving a reason, how addition and condensation polymerization compare with regard to green chemistry.

Draw the full structural formula of the organic functional group formed during the polymerization of the two reactants below.

MWCNT are very small in size and can greatly increase switching speeds in a liquid crystal allowing the liquid crystal to change orientation quickly.

Discuss two other properties a substance should have to be suitable for use in liquid crystal displays.

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.

Outline how resistance to electric currents occurs in metals.

Suggest why the resistance of metals increases with temperature.

State two differences between Type I and Type II superconductors.

1.40 × 10⁻³ g of NaOH (s) are dissolved in 250.0 cm³ of 1.00 × 10⁻¹¹ mol dm⁻³ Pb(OH)₂ (aq) solution.

Determine the change in lead ion concentration in the solution, using section 32 of the data booklet.

Explain why Type 2 superconductors are generally more useful than Type 1.

Draw the structure of the monomer from which nylon-6 is produced by a condensation reaction.

Deduce, giving a reason, whether the atom economy of a condensation polymerization, such as this, would be greater or less than an addition polymerization, such as the formation of HDPE.

State the number of atoms in the unit cell.

Determine the density of calcium, in g cm⁻³, using section 2 of the data booklet.

Ar = 40.08; metallic radius (r) = 1.97 × 10⁻¹⁰ m

Explain how entropy affects this equilibrium.

State the number of coordinate covalent bonds EDTA forms with Ni²⁺.

Describe the effect of infrared (IR) radiation on carbon dioxide molecules.

Outline one approach to controlling industrial emissions of carbon dioxide.