Question 1

Paper 2Hard11 marks

A controlled preparation is used to investigate the ionic composition of an iron sulfide solid. Each batch contains 12.0×10−3 mol12.0\times10^{-3}\ \mathrm{mol} of iron ions of unknown charge. Different amounts of sulfide ions, S2−\mathrm{S^{2-}} are added. Assume that the iron ions keep the same charge throughout, no redox occurs, and the only solid formed contains iron and sulfide ions.

Figure 1 shows the measured mass of dried solid for each amount of sulfide added. A preliminary report identifies the solid as iron(III) sulfide, Fe2S3\mathrm{Fe_2S_3}

0246810121416182000.20.40.60.811.2Amount of S2- added / 10-3 molMass of dried solid / g
(a)

Describe the pattern in the graph as more sulfide ions are added, and identify the ion that limits formation of the solid beyond the plateau.

[2]
(b)

Use Figure 1 to assess the preliminary report. Deduce the simplest formula and name of the solid.

[5]
(c)

Write balanced equations showing the electron transfer from a neutral iron atom and to a neutral sulfur atom for the ions in the solid identified in (b).

[2]
(d)

Explain the nature of the bonding between the ions in the solid identified in (b).

[2]

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