Return to Chemistry, UWI-Mona, Home Page 1) Write down the systematic name for each of the following complexes and indicate the coordination number, oxidation state, stereochemistry and magnetic moment of the central ion.
a) K4[Mn(CN)6] b) [Co(NH3)5Cl]Cl2 c) Cs[FeCl4] d) K [Cr(oxal)2(H2O)2]·3H2O e) Copy3Cl3 f) [Ni(en)2Cl NH3] Cl g) [Cu(NH3)4]SO4·2H2O
2) The hexaquo manganese(II) ion contains five unpaired electrons, while the hexacyano- ion contains only one unpaired electron. Explain, using Crystal Field Theory.
3) Indicate the type of isomerism exhibited by the following complexes and draw structures for these isomers.
a) K[Cr(oxal)2(H2O)2]·3H2O b) [Co(en)3]Cl3 c) [Co(NH3)5NO2](NO3)2 d) PtCl2NH3H2O
4) Discuss complex ion formation and the Chelate Effect.
5) Give an example of each of the following:
a) Binuclear Complex b) Metal Chelate c) Low spin complex d) High spin complex e) Five coordinate complex.
6) The complex ion [Ni(NH3)4]2+, forms on mixing aqueous solutions of ammonia and a nickel salt.
a) If a solution contains 1.6 · 10-4 % of the nickel ions in the form
of Ni2+ when the concentration of free NH3 (aq) is 0.5M. What is the
stability constant of the complex [Ni(NH3)4]2+?
(Assume that this is the only complex present).
b) The octahedral ammine complex can be prepared by using a solution of ammonia which has been supersaturated with ammonia gas, such that:
log K5 = 0.85 log K6 = 0.42. Calculate the overall ß6 for [Ni(NH3)6]2+. Write the equations for the equilibria corresponding to K5 and K6. Ans. a) 1.0 · 107. b) 1.9 · 108.
7) a) Draw the complex, [Ni(en)3]2+, showing the optical isomers.
b) If at equilibrium, [Ni(en)3]2+, is
0.08M and [en] is 0.40 M, calculate [Ni2+].
Note that ß3 for [Ni(en)3]2+
is 4.07 · 1018.
c) Write equations for the successive formation equilibria.
d) The first and second stepwise formation constants are:
log K1 = 7.66 and log K2 = 6.40 . Calculate the third stepwise formation constant. Ans b) 3.07 · 10-19. d) 3.55 · 104 .
8) a) Place the following ligands in increasing order in the Spectrochemical series:
CN-, NH3, Cl-, H2O
b) For octahedral first row transition metal complexes with between four and seven d electrons, both high and low spin electron configurations are possible.
Use Crystal Field splitting diagrams to determine the number of unpaired electrons and then calculate the expected spin-only magnetic moments.
1) The stepwise enthalpies DHn and the stability constants K for the system Ni2+ - en in aqueous solution at 298°K are as follows: n 1 2 3 DHn kJ mol-1 -37.7 -38.4 -40.6 log10 Kn 7.51 6.35 4.42 Calculate the standard free energy DG and entropy changes DS associated with the addition of each ligand. 2) Calculate the entropy changes for the following reactions at 298°K and comment on the results: Zn2+ + 2NH3 <=> Zn(NH3)22+ DH=-28.03 kJ mol-1 Log b2 = 5.01 Zn2+ + en <=> Zn(en)2+ DH=-27.6 kJ mol-1 Log b2= 6.15 (NB R=8.314 J K-1 mol-1) 3) Calculate the overall complex dissociation equilibrium constant for the Cu(NH3)42+ ion given that b4 for this complex is 2.1 · 1013. 4) Calculate the equilibrium concentration of the Fe3+ ion in a solution that is initially 0.10 M Fe3+ and 1.0 M SCN-, given that b2 for Fe(SCN)2+ = 2.3 · 103. 5) Calculate the equilibrium concentration of the Cu2+ ion in a solution that is initially 0.10 M Cu2+ and 1.0 M NH3, given that b4 for Cu(NH3)42+= 2.1 · 1013. 6) and 7) from tutorial paper. 8) What is the ratio of uncomplexed to complexed Zn2+ in a solution that is 10M in NH3 given that b4 for Zn(NH3)42+ = 3 · 109. 9) Given the following data at 25°C: DG = -41.4 kJ mol-1 for Ag+(aq) + 2NH3 <=> Ag(NH3)2+(aq) and DG = -55.6 kJ mol-1 for Ag+(aq) + Cl- <=> AgCl(s) a) Calculate DG for AgCl(s) + 2NH3 <=> Ag(NH3)2+(aq) + Cl- b) Calculate the equilibrium constant for this reaction. Will the reaction proceed from L -> R ??
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Created Feb 1995. Last modified 22th April 1999.
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