Magnetic Moments - Inorganic Chemistry - Exam, Exams for Inorganic chemistry. Aliah University

Inorganic chemistry

Description: Magnetic Moments, Distinguish Square Planar, Octahedral Coordination Compounds, Octahedral Geometry, Coordination Compounds, High Spin, Square Planar Complex, Bromide and Ammonia, Octahedral Transition Metal, Ammonia and Chloride. This is inorganic chemistry past paper from some university. I hope it serve purpose of your searching for exams.
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Spring Examinations 2011 / 2012
Exam Code(s) 3BPC2
Exam(s)
Module Code(s) CH319 Inorganic Chemistry
Module(s)
Paper No. I
External Examiner(s) Professor K. Molloy
Internal Examiner(s) Dr. A. Erxleben, Dr. T. Higgins, Dr. L. Jones
Instructions:
Answer four questions.
Answer at least one question from each section.
All questions carry 25 marks distributed as shown. Leave the first page of
the Answer Book blank and list on it clearly the numbers of the questions
attempted.
Duration
2 hrs
No. of Pages 3 Following this page
Discipline(s) Chemistry
Requirements log tables with periodic table
Section A
Answer at least one question from this section
1. Answer each of the following:
(a) Show how magnetic moments can be used to distinguish square planar and
octahedral coordination compounds of Ni(II). Explain why the magnetic
moments are different. [7 marks]
(b) Show how the Jahn-Teller Theorem can be used to account for the tetragonal
distortion from octahedral geometry that is found in coordination compounds of
Cu(II) and of high spin Cr(II). [7 marks]
(c) Explain why coordination compounds of Pd(II) and Pt(II) are generally square
planar while those of Ni(II) are often octahedral. [6 marks]
(d) Given the task of attempting to synthesise a square planar complex of Ni(II) what
ligand(s) would you use. Explain your choice. [5 marks]
2. Answer each of the following:
(a) Explain the symbols Eg, T2g, A1g and T1u as they are used in Molecular Orbital
(MO) diagrams. Give one example in each case of either an atomic or molecular
orbital for which each of the above symbols are appropriate symmetry labels.
[5 marks]
(b) Describe how the ligands bromide and ammonia differ in their bonding with
transition metal cations. [5 marks]
(c) Describe the differences in MO diagrams for octahedral transition metal
coordination compounds of ammonia and chloride. [10 marks]
(d) Explain why ammonia is higher in the spectrochemical series than water.
[5 marks]
Section B
Answer at least one question from this section
3. Answer each of the following:
(a) Describe the structure of metallo-proteins clearly showing both the protein
structure and how amino acid side chains coordinate metal ions. [8 marks]
(b) Describe the role calcium plays in biological systems and illustrate your answer
with an example. [8 marks]
(c) Give one example of a zinc metallo-protein. Draw a structure for the active metal
centre and clearly identify the ligands that coordinate the metal. Describe the role
this protein plays in biological systems. [9marks]
more on the next page
4. Answer each of the following:
(a) The water exchange reaction for [Cr(NH3)5(H2O)]3+ proceeds via an associative
mechanism.
(i) Write equations to describe the mechanism of this reaction.
(ii) Sketch the reaction profile. Clearly indicate intermediates, transition states
and Gibbs energies of activation.
(iii) Explain how you would determine the Gibbs energy of activation.
[17 marks]
(b) The rate constants for the reduction of [Co(NH3)5(H2O)]3+ and of
[Co(NH3)5(OH)]2+ by [Cr(H2O)6]2+ have been measured. Comment (with
reference to possible reaction mechanisms) on the data below. Describe possible
reaction mechanisms in detail.
[Co(NH3)5(OH)]2+ + [Cr(H2O)6]2+ [Co(NH3)5(OH)]+ + [Cr(H2O)6]3+
k = 1.5 x 106 M-1 s-1
[Co(NH3)5(H2O)]3+ + [Cr(H2O)6]2+ [Co(NH3)5(H2O)]2+ + [Cr(H2O)6]3+
k = 0.1 M-1 s-1
[8 marks]
Section C
Answer at least one question from this section
5. Answer each of the following:
(a) Give two examples of ligands which may be classed as:
(i)
-donors
(ii)
-donors
(iii)
-acceptors
(iv)
-donors and
-acceptors [8 marks]
(b) Explain how certain ligands can exhibit both -donor and -acceptor behaviour
(as in (iv) above). Indicate how substitution effects influence the -donor and -
acceptor strengths. [5 marks]
(c) For each of the following organometallic complexes give the metal valence
electron count and ratify in each case whether the 18-electron rule is obeyed.
Show your workings clearly.
(i) [(η5-C5H5)Ni(-PPh3)]
(ii) [(η5-C5H5)2Co](BF4)
(iii)[Cr(η5-C5H5)(η3-allyl)(η4-buta-1,3-diene)]
(iv) [RhCl(H)2(η2-C2H4)(PPh3)2]
[12 marks]
more on the next page
6. Answer each of the following:
In 2005 R. R. Schrock, Y. Chauvin and R. H. Grubbs were awarded a Nobel Prize in
Chemistry for their discovery and development of olefin metathesis using novel
organometallic complexes as catalysts for this chemistry.
(a) Confirm whether the following complex (a Grubbs catalyst used in olefin
metathesis) obeys the 18-electron rule:
[5 marks]
(b) Deduce the oxidation state of the Ru metal ion in the above complex.
[5 marks]
(c) Briefly explain the term olefin metathesis and give three reasons why the
discovery and progression of this chemistry (including the catalysts) was / is so
important. Use a sketch to aid your answer. [15 marks]
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