CIE Nov 2014 v2 Paper 4 Q3

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PMT (a) Natural phosphorus consists of one isotope, 31P. Chlorine exists naturally as two isotopes, 35Cl and 37Cl, in the relative abundance ratio of 3 : 1. (i) The mass spectrum of PCl 3 contains several peaks corresponding to a number of molecular fragments. Suggest the isotopic composition of the fragments with the following mass numbers. mass number isotopic composition 101 103 105 (ii) Predict the relative ratios of the peak heights of the three peaks corresponding to these fragments.[4] (b) Phosphorus reacts with chlorine to form a variety of chlorides. PCl 5 is an example of a compound that exists as two structures depending on the conditions. 2PCl 5(g) [PCl 4]+[PCl 6](s) (i) Draw a dot-and-cross diagram to show the bonding in PCl 5. Show the outer electrons only.UCLES 2014 9701/42/O/N/14<br /> (ii) Draw diagrams to suggest the shapes of [PCl 4]+ and [PCl 6]. PMT [PCl 4]+ [PCl 6] [3] (c) (i) Phosphorus(III) oxide, P4O6, contains no PP or OO bonds. In the P4O6 molecule, all oxygen atoms are divalent and all phosphorus atoms are trivalent. Sketch a structure for P4O6. (ii) P4O6 can act as a ligand. What is meant by the term ligand ?[2] (d) Phosphate ions in water can be removed by adding a solution containing Ca2+(aq) ions, which form a precipitate of calcium phosphate, Ca3(PO4)2. (i) Write an expression for the Ksp of Ca3(PO4)2. Ksp = (ii) The solubility of Ca3(PO4)2 is 2.50106 mol dm3 at 298 K. Calculate the solubility product, Ksp, of Ca3(PO4)2 at this temperature. Include the units. Ksp =units[4]UCLES 2014 9701/42/O/N/14 [Turn over<br /> PMT (e) (i) What is meant by the term lattice energy?(ii) Explain why the lattice energy of calcium phosphate is less exothermic than that of magnesium phosphate.[3] [Total: 16]UCLES 2014 9701/42/O/N/14<br /> PMT Question 4 starts on the next page.UCLES 2014 9701/42/O/N/14 [Turn over<br />

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