Search in the document preview
Ollscoil na hÉireann, GaillimhNational University of Ireland, Galway
Semester I Examinations, 2010/2011
Exam Code(s) 2BS1, 2BY1, 2EH1, 2EV1, 2BPP1, 2BPC1 Exam(s) Module Code(s) CH204 Inorganic Chemistry Module(s) Paper No. 1 Repeat Paper Special Paper External Examiner(s) Professor K. Molloy Internal Examiner(s) Dr. A. Erxleben, Dr. T. Higgins Instructions:
Answer 4 questions. Answer 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 Hr. No. of Answer books Requirements: Handout MCQ Statistical Tables Graph Paper Log Graph Paper Other Material log tables with periodic table No. of Pages 5 Following this page Department(s) Chemistry
Section A Answer one question from this section
1. Answer each of the following: (a) What is the origin of temporary and permanent hardness of water? Explain why temporary
hardness can be removed by boiling. [5 marks] (b) Outline a gravimetric procedure that you could adopt to determine the nickel content of a
solution containing nickel, but no other metal ions. Clearly refer to any precautions that would be necessary within the procedure in order to obtain an accurate analysis. [6 marks]
(c) With the help of the half-equations and redox potentials provided below, write balanced
equations for the following reactions: (i) K2Cr2O7 + HCl + Zn [5 marks] (ii) FeCl3 + KI E (Volts) Zn2+ + 2 e- = Zn -0.763 Cr3+ + e- = Cr2+ 0.41 1/2 I2 + e
- = I- 0.536 Fe3+ + e- = Fe2+ 0.77 Cr2O72
- + 14 H+ + 6 e- = 2 Cr3+ + 7 H2O 1.33 1/2 Cl2 + e
- = Cl- 1.36
(d) Explain the following: (i)A colour change takes place when a basic aqueous potassium chromate solution is acidified.(ii)The addition of sodium hydroxide to a copper sulphate solution results in the
formation of a bluish precipitate, whereas the addition of excess ammonia solution results in the formation of a deep blue solution that does not contain a precipitate.
(iii)A colour change to green is observed, when NaOH is added to KMnO4 until the solution is alkaline.[9 marks]
... more on the next page
2. Answer each of the following: To determine the hardness of tap water, the following experiment has been carried out: To 50 cm3 of tap water buffer (pH 10) and ErioT indicator were added. The solution was titrated with 1.035 x 10-2 M EDTA-Mg solution. 7.8 cm3 EDTA solution were required for the titration. Then 250 cm3 of tap water were boiled for 20 minutes. The solution was cooled, filtered into a 250 cm3 volumetric flask and diluted to the mark with distilled water. 50 cm3 of this solution were mixed with buffer (pH 10) and ErioT indicator and titrated with 1.035 x 10-2 M EDTA-Mg solution. 7.1 cm3 EDTA-Mg solution were used. (a) Draw the structure of EDTA. [3 marks] (b) Calculate the temporary hardness as mg CaCO3 per dm3. [22 marks] Atomic weights: Ca: 40 C: 12 O: 16
Section B Answer one question from this section
3. Answer each of the following: (a) Define the following terms: (i) LUMO (ii) antibonding molecular orbital (iii) van der Waals radius. [3 marks](b) Construct the MO diagram of B2. Calculate the bond order and predict whether the
molecule is paramagnetic or diamagnetic. [10 marks] (c) Provide an energy vs. distance plot for the approach of two hydrogen atoms and explain the
form of the plot. [6 marks] (d) Use the Valence Shell Electron Pair Repulsion Theory to derive the geometry of the
following: [6 marks] (i) SbCl5 (ii) BrF3 (iii) SnCl3-. ... more on the next page
4. Answer each of the following: (a) Define the following terms: (i) polymorph (ii) substitutional alloy [6 marks](b) What is the coordination number of (i) a sphere in a cubic close-packed structure (ii) Na+ in the NaCl lattice [4 marks] (c) Describe the antifluorite lattice in one sentence. [4 marks] (d) Sketch the unit cell of the CsCl lattice. Show that the structure of the unit cell is consistent
with the formula CsCl. [5 marks] (e) Calculate the standard enthalpy of formation fH of CaF2 from the following data: lattice enthalpy of CaF2, latticeH(CaF2) = -2643 kJ mol-1 enthalpy of atomization of Ca, aHº(Ca,s) = 178 kJmol-1 first ionization energy of Ca, IE1 = 590 kJ mol-1 second ionization energy of Ca, IE2 = 1145 kJ mol-1 dissociation enthalpy of F2, D(F2,g)= 158 kJ mol-1 electron affinity of F, EAH(F,g) = -328 kJ mol-1 [6 marks]
Section C Answer one question from this section
5. Answer each of the following: (a) Describe the crystal field splitting pattern for octahedral complexes of transition metals. [5 marks] (b) Use crystal field theory to explain why compounds of first row transition metals are
coloured and to account for the visible spectrum of the cation, [Ti(H2O)6] 3+.
[6 marks] (c) Arrange the following ligands in order of increasing field strength, Br-, F-, CN-, NH3,
H2O, and account for differences in the visible spectra of the complex ions [Ti(H2O)6] 3+
(λmax = 493nm) and [TiF6]3- (λmax = 588nm). [6 marks](d) Predict the spin only magnetic moments of the following compounds.
[V(H2O)6] 3+ ; [CoBr6]
3- ; [Cr(CN)6] 4- ; [Cu(NH3)6]
2+ [8 marks]... more on the next page
6. Answer five of the following: (a) Give the valence shell electronic configuration of iron in the complex ions, [Fe(H2O)6]2+
and [FeCl6] 3-.
(b) Give molecular formulae and draw structures for, (i) a hexa-aqua coordination compound
of a transition metal with d6 electronic configuration and (ii) a hexaamine coordination compound of a transition metal with a d7 electronic configuration.
(c) Draw structures for all isomers of the complex cations, [Cr(acac)2(H2O)2]+ and
[Cr(acac)3]: where acac is the acetylacetonate anion. (d) Draw structures for the mer and fac isomers of the coordination compound
[RhCl3(PMe3)3]. (e) Draw a structure for the complex ion trans-[ScCl2(benzo-15-crown-5)] +. (f) Give molecular formulae and draw structures for the products formed when an aqueous
solution of ferric chloride is reacted with potassium oxalate. [5 marks each part]
Section D Answer one question from this section
7. Answer each of the following: (a) Compare the allotropes of carbon, graphite and diamond, with regard to structure, bonding
and properties. [10 marks](b) Write balanced equations for the following reactions: (i) SiF4 with NaF (ii) PbS with ozone. [4 marks] (c) Describe thevarious steps of theproduction of ultrapure silicon starting from SiO2. [7 marks] (d) Explain why O2 is a gas at room temperature, while sulfur is a solid. [4 marks]... more on the next page
8. Answer each of the following: (a) Write a brief note on the diagonal relationship shown by the pairs Li/Mg and Be/Al. For
each pair, provide two examples of the diagonal relationship. [7 marks] (b) Describe the structure of and bonding in BeCl2. [4 marks](c) What is meant by the thermodynamic 6s inert pair effect? [4 marks](d) Comment on the following: In contrast to Mg2+, Be2+ does not form a stable complex with EDTA. [4 marks] (e) Write balanced equations for the following reactions: (i) Ca with H2O (ii) Al(OH)3 with H2SO4 (iii) BeF2 with an excess of NaF. [6 marks]