Upon heating of a mixture of A and fluorine (molar ratio 1 : 9, pressure approximately 1 MPa) to 900°C three compounds ( B, C and D) are formed. All three products are crystalline solids at ambient temperature with melting points below 150°C. The fluorine content of C is found to be 36.7 % and that of D 46.5% (by weight). When B is treated with anhydrous HOSO2F at -75°C a compound E is formed:
B+ HOSO2F → E + HF
E is a solid which is stable for weeks at 0°C, but decomposes in days at room temperature. The electron density distribution of E obtained through X-ray diffraction studies is shown on two intersecting, mutually perpendicular planes (see Fig. 1).
The numbers indicated on the maps relate to the electron density in the neighbourhood of the atoms of E as a function of the spatial coordinates. The maxima found in these maps coincide with the locations of the atoms and the values are approximately proportional to the number of electrons in the atom in question.
(a) Show where the maxima lie by drawing the contour curves around the maxima, connecting points of equal electron densities. Label each maximum to show the identities of the atoms in E.
(b) When 450.0 mg of C was treated with an excess of mercury, 53.25 ml of A was liberated at a pressure of 101.0 kPa and a temperature of 25°C. Calculate the relative atomic mass of A.
(c) Identify A, B, C, D and E.
(d) Use the valence-shell electron-pair repulsion theory (VSEPR) to propose electron-pair geometries for B and C. Using the two electron density maps, sketch the molecular geometry of E. The original mixture was hydrolysed in water. B reacts to A while liberating oxygen and producing aqueous hydrogen fluoride. Hydrolysis of C leads to A and oxygen (in molar ratio of 4 : 3) and yields an aqueous solution of AO3 and hydrogen fluoride. D hydrolyses to an aqueous solution of AO3 and hydrogen fluoride.
(e) Write the equations for the three hydrolysis reactions.
(f) Quantitative hydrolysis of a mixture of B, C and D gives 60.2 ml of gas (measured at 290 K and 100 kPa). The oxygen content of this gas is 40.0% (by volume). The amount of AO3 dissolved in water is titrated with an aqueous 0.1 molar FeSO4 solution and 36.0 ml used thereby. During the titration Fe2+ is oxidized to Fe3+ and AO3 is reduced to A. Calculate the composition (% by moles) of the original mixture of B, C and D.