When phosphorus pentachloride, PCl5\text{PCl}_5PCl5, and ammonium chloride, NH4Cl\text{NH}_4\text{Cl}NH4Cl, are heated together, hexachlorocyclotriphosphazene, P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6, is formed together with hydrogen chloride, HCl\text{HCl}HCl, gas.
P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6 has a cyclic structure consisting of alternating phosphorus and nitrogen atoms. This ring structure can be represented with alternating single and double bonds, analogous to the Kekulé structure of benzene.
Write a balanced equation for the reaction of PCl5\text{PCl}_5PCl5 and NH4Cl\text{NH}_4\text{Cl}NH4Cl to form P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6.
Calculate the percentage by mass of phosphorus, P\text{P}P, in P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6. Give your answer to 2 decimal places. (Use relative atomic masses: Ar(P)=31.0A_r(\text{P}) = 31.0Ar(P)=31.0, Ar(N)=14.0A_r(\text{N}) = 14.0Ar(N)=14.0, Ar(Cl)=35.5A_r(\text{Cl}) = 35.5Ar(Cl)=35.5.)
Suggest one example of physical or chemical evidence that would show P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6 has a structure with localized double bonds rather than a fully delocalised structure.
In a molecule of P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6, all the Cl\text{Cl}Cl atoms are bonded to P\text{P}P atoms, so that each phosphorus atom has two chlorine substituents. Suggest a possible cyclic molecular structure for P3N3Cl6\text{P}_3\text{N}_3\text{Cl}_6P3N3Cl6 showing all bonds in the molecule.
