Answers to questions on Metals & ICP spectroscopy

1. (a) Alumina melts at 2045 ^oC. The molten solution of alumina in cryolite melts at about 950 ^oC so much less energy is needed to obtain liquid aluminum(III) ions.

(b) Cathode (−) : Al³⁺(l) + 3e⁻ → Al(l)
Anode (+) : 2O²⁻(l) → O₂(g) + 4 e⁻

(c) Some of the oxygen gas released reacts with the graphite anode to form carbon dioxide.
C(s) + O₂(g) → CO₂(g)

(d) The carbon dioxide released from the anode is a greenhouse gas .
The fuel used to provide the electricity and/or to transport the raw materials to the plant and to transport the mIB Docs (2) Teamfactured alumimiun to the customers may well be a fossil fuel, which burns to produce carbon dioxide.

2. (a) Silver anode: Ag(s) → Ag⁺(aq) + e⁻
Copper cathode: Ag⁺(aq) + e⁻ → Ag(s)

(b) To keep the concentration of dissolved silver ions constant so that there are sufficient silver ions to plate the copper as they would all be used up before the plating was complete if an inert electrode was used.

(c) Volume of silver = 600 x 3.00 x 10^-3 = 1.80 cm³
Mass of silver = volume x density = 1.80 x 10.5 = 18.9 g

(d) Amount of silver required = 18.9 / 107.87 = 1.75 x 10^-1 mol
Charge required = 1.75 x 10^-1 x 9.65 x 10⁴ = 1.69 x 10⁴ C
Time = 1.69 x 10⁴ / 5 x 10^-1 = 3.38 x 10⁴ seconds (9 hours 39 minutes).

3. (a) Suspend the material in an external magnetic field. If it is paramagnetic it will be slightly attracted by the magnetic field. This can be shown by the fact that it will weigh differently in the external field compared to when the external field is removed. If it is diamagnetic no difference will be observed in weight when it is suspended in an external magnetic field.

(b) (i) chlorine atoms: paramagnetic. The electron configuration is 1s²2s²2p⁶3s²3p⁵ so it contains one unpaired electron.
(ii) chloride ions: diamagnetic. The electron configuration is 1s²2s²2p⁶3s²3p⁶ so there are no unpaired electrons.
(iii) zinc metal: diamagnetic. The electron configuration is [Ar]4s²3d¹⁰ so it contains no unpaired electrons.
(iv) iron(III) ions: paramagnetic. The electron configuration is [Ar]3d⁵ so it contains five unpaired electrons.

4. (a) Plasma is a highly energized ‘cloud’ of gaseous ions (charged particles) and their electrons.

(b) The emitted radiation has peaks of light with characteristic wavelengths that correspond to the emission spectra of all the elements contained within the sample. By calibrating the machine with specific amounts of known elements, the concentration of each element present can be determined, as the concentration is proportional to the intensity of the peaks.

(c) aluminium (27), manganese (55) and arsenic (75).

Answers to Metals & ICP spectroscopy questions