Explain these properties of carbon nanotubes.

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.

Write the half-equations for the reactions occurring in this electrolysis.

Calculate the theoretical mass of magnesium obtained if a current of $3.00 \mathrm{A}$ is used for $10.0$ hours. Use charge $\left(Q\right)=current(I )\times time(t )$ 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.

Excellent strength: defect-free AND rigid/regular 2D/3D ✔

Excellent conductivity: delocalized electrons ✔

Accept “carbons/atoms are all covalently bonded to each other” for M1.

Any of:
ductility ✔
strength/resistance to deformation ✔
malleability ✔
hardness ✔
resistance to corrosion/chemical resistance ✔
range of working temperatures ✔
density ✔

Do not accept “conductivity”.

Anode: $2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}$ ✔

Cathode: ${\mathrm{Mg}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Mg}\left(\mathrm{l}\right)$ ✔

Accept $C{l}^{-}\to C{l}_2\left(g\right)+e^{–}$.

Award [1 max] for correct equations at incorrect electrodes.

$«Q=I\times t=3.00\times 10.0\times 3600=»108 000 \mathrm{C}$ ✔

$«\frac{Q}{F}=\frac{108 000 C}{96 500 C {\mathrm{mol}}^{-1}}=»1.12«\mathrm{mol} {\mathrm{e}}^{-}»$ ✔

$«\frac{1.12 \mathrm{mol}}{2}=0.560 \mathrm{mol} \mathrm{Mg}»$
$«m=0.560 \mathrm{mol}\times 24.31 \mathrm{g} {\mathrm{mol}}^{-1}=»13.6«\mathrm{g}»$ ✔

Award [3] for correct final answer.

argon/$\mathrm{Ar}$/helium/$\mathrm{He}$ ✔

Accept any identified noble/inert gas.
Accept name OR formula.

Do not accept “nitrogen/$N_2$“.

pores/cavities/channels/holes/cage-like structures ✔

«only» reactants with appropriate/specific size/geometry/structure fit inside/go through/are activated/can react ✔

Accept “molecules/ions” for “reactants” in M2.

rod-shaped molecules
OR
«randomly distributed but» generally align
OR
no positional order AND have «some» directional order/pattern ✔

Accept “linear” for “rod-shaped”.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.

This was a very popular option with approximately 34% of candidates attempting Option B. Many students appeared well prepared for this option. Some candidates continue to provide answers with a heavy Biology bias that often make them lose valuable points.