| Date | May 2016 | Marks available | 4 | Reference code | 16M.3.hl.TZ0.3 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain and Outline | Question number | 3 | Adapted from | N/A |
Question
Iron may be extracted from an ore containing Fe2O3 in a blast furnace by reaction with coke, limestone and air. Aluminium is obtained by electrolysis of an ore containing Al2O3.
(i) Outline the cause of electrical resistance in metallic conductors.
(ii) The resistance of two metals was measured as a function of temperature. The following graph was obtained.
Explain the behaviour of metal II below temperature X in terms of the Bardeen–Cooper–Schrieffer (BCS) theory.
(i) Polonium metal has a simple cubic structure. Construct a unit cell diagram and state the coordination number of each atom.
(ii) X-ray diffraction was carried out on polonium using radiation with a wavelength of 8.80×10−11 m. The first order maximum in the diffraction pattern was observed at an angle of 13.0°. Determine the distance, in m, between layers of polonium atoms using section 1 of the data booklet.
Markscheme
(i)
collisions between electrons AND positive ions/cations/metal atoms/metal lattice
Accept “irregularities/non-uniformity in metal lattice «caused by impurities» but do not accept just “impurities present”.
Do not accept “attractions” for “collisions”.
(ii)
metal II is a superconductor
passing electrons «slightly» deform lattice/displace positive ions/cations AND couple/form Cooper pairs/condense with other electrons
energy propagates along the lattice in wave-like manner/as phonons
Cooper pair/electron condensate moves through lattice freely
OR
phonons are «perfectly» elastic/cause no energy loss
(i)
«coordination number =» 6
Do not accept diagram of a lattice showing multiple unit cells.
(ii)
«Bragg equation, n=1»
«d=\(\frac{{8.80 \times {{10}^{ - 11}}}}{{2 \times \sin \left( {13.0} \right)}}\)»1.96×10-10«m»
