Question 23M.3.SL.TZ2.3
| Date | May 2023 | Marks available | [Maximum mark: 10] | Reference code | 23M.3.SL.TZ2.3 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Calculate, Deduce, Describe, Explain, Identify, Outline, Suggest, Write | Question number | 3 | Adapted from | N/A |
Most metals have to be extracted from an ore. The way in which this is carried out depends on the reactivity of the metal.
Identify a metal produced by reacting its oxide with carbon or carbon monoxide. Use section 25 of the data booklet.
[1]
Any one of:
Zn, Cr, Fe, Cd, Co, Ni, Sn, Pb, Sb, As, Bi, Cu, Ag, Pd, Hg, Pt ✓
Accept “Au”.
Accept name or symbol of metal.
Aluminium is produced by electrolytic reduction of a solution of aluminium oxide, Al2O3, in molten cryolite, Na3AlF6.
Write the half equation for the reaction at the electrode where aluminium is formed.
[1]
Al3+ + 3 e− → Al(l) ✓
Do not penalize if equilibrium arrow used.
Calculate the atom economy for the production of aluminium from its oxide, assuming the products do not react with the electrodes. Use section 1 of the data booklet.
[1]
« × 100 =» 52.92 % ✓
Accept “0.5229”.
Suggest one factor, other than atom economy, that indicates the production of aluminium from its ore has a significant environmental impact.
[1]
high energy consumption «that has environmental implications»
OR
large amounts of waste «produced by mining and purification of the ore»
OR
mining has negative impact on landscape
OR
greenhouse gas/pollution from transport/machinery ✓
Accept “fluorine/fluorine compounds produced" or their formulas.
OR
“carbon dioxide/carbon monoxide released”.
Deduce why pure molten aluminium oxide is a poor conductor of electricity. Use sections 8 and 29 of the data booklet.
[2]
average electronegativity 2.5 AND
electronegativity difference 1.8 ✓
border between ionic and «polar» covalent ✓
Accept “partially covalent/high covalent character” for M2.
Award [2] for calculation of %ionic character = «1.8/3.2 =» 56%.
Inductively coupled plasma (ICP) techniques can be used to estimate the concentration of other metals in the aluminium produced.
Describe the plasma state.
[1]
electrons AND «positive» ions «in gaseous state» ✓
Accept “gaseous atoms, «many of» which have lost their electrons”.
Do not accept “gaseous ions” alone.
Explain how different metals are identified, and their concentrations determined, if ICP is coupled with Optical Emission Spectroscopy (OES).
Identification: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Concentration: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
[2]
Identification:
«emit» light/photons of characteristic frequencies ✓
Concentration:
intensity/brightness of light «proportional to concentration» ✓
For M1 accept “energies/wavelengths” for “frequencies”.
For M2 accept “signal strength/peak height”.
Do not accept a general statement such as “concentrations can be detected by absorbance of the radiation «in OES»” for M2.
An aluminium matrix can be reinforced with carbon nanotubes. Outline why carbon nanotubes are so strong and rigid.
[1]
«held together by strong» covalent bonds «and defect free/regular 2D/3D» ✓