School of Chemistry, Durban s CHEM261: APPLIED INORGANIC CHEMISTRY FOR CHEMICAL ENGINEERS Duration: 2 hours Total marks: 100 External Examiner: Internal Examiner: Dr M Bala University of KwaZulu- Natal Dr S Singh IMPORTANT: Complete this section immediately. Student No: Seat Number: Name (optional): INSTRUCTIONS: 1. Answer ALL questions. 2. Calculators may be used but all working must be shown. 3. The pages of this question paper must not be unpinned. 4. Your answers must be written on the question paper in the spaces provided. The reverse pages may be used for extra space or for rough work. 5. You must write legibly in black or blue ink. Pencils and Tipp-Ex are not allowed. 6. This question paper consists of 15 pages including a periodic table. Please check that you have them all. Question No. 1 2 3 4 5 6 7 Total Internal Mark External Mark Total Mark 13 13 20 14 18 12 10 100
QUESTION 1 School of Chemistry Page 2 (a) Sodium hexanitrocobalt, Na 3 [Co(NO 2 ) 6 ], is prepared in the laboratory by reacting potassium- free sodium nitrite with cobalt nitrate hexahydrate. (i) Write down the balanced ionic equation for this reaction. (2) (ii) What is the coordination number of Co in this compound? (1) (iii) What is the oxidation state of Co in the above compound? (1) (iv) Draw the structure of the complex and state its preferred molecular geometry. (3) (v) Write the outer electron configuration of Co and Co 2+. (2)
School of Chemistry Page 3 (b) Name the following coordination complexes: (i) [Cr(NH 3 ) 6 ] 3+ (1) (ii) [Co(NH 2 CH 2 CH 2 NH 2 ) 3 ]Cl 3 (1) (c) Write the structures of the following coordination complexes: (i) Potassium diamminetetrabromocobaltate(iii) (1) (ii) hexachloroplatinate(iv) (1) [13]
QUESTION 2 (a) School of Chemistry Page 4 With the aid of named structures, indicate the types of isomerism that are possible for complexes with the following molecular formulas: (i) [PtCl 5 (SCN)] 2- (4) (ii) [CoCl 3 (NH 3 ) 3 ] (4)
School of Chemistry Page 5 (b) Explain very briefly with the aid of structures, the chelate effect with regards to stability of complexes. (5) [13]
QUESTION 3 School of Chemistry Page 6 (a) With the aid of labelled energy level diagrams, indicate the occupancy of the orbitals in d 6 octahedral high- and low- spin complexes. (4) (b) The magnetic moment of the complex [Mn(NCS) 6 ] 4- is 6.06 µ B. (i) Determine its preferred electron configuration. Show all calculations. (5)
School of Chemistry Page 7 (ii) Calculate the ligand field stabilization energies (LFSE) for both the highspin and low-spin states. (4) (c) Using the spectrochemical series, write down the preferred electronic configuration in the form, t 2g e g for the complexes, [Fe(OH 2 ) 6 ] 2+ and [Fe(CN) 6 ] 3-. (4) (d) Calculate the number of unpaired electrons in [Fe(CO) 6 ] 3+ if µ = 5.92 µ B. (3) [20]
QUESTION 4 (a) School of Chemistry Page 8 Explain the following terms: (i) crystalline solid (1) (ii) unit cell (1) (iii) lattice point (1) (iv) cubic close packing (3)
School of Chemistry Page 9 (b) Rubidium metal has a body- centred cubic structure. The density of the metal is 1.532 g cm -3. (i) Sketch the unit cell and calculate the number of lattice points. (4) (ii) Calculate the edge length of the unit cell in picometres. (4) [14]
QUESTION 5 School of Chemistry Page 10 (a) The figure below shows the NaCl crystal structure The smaller spheres represents the Na + ions and the larger ones the Cl - ions. (i) How many Na + and Cl - ions are present in the above structure? (2) (ii) Calculate the shortest distance between a pair of Cl - ions in terms of the edge length, a. (Hint: Diagram for the calculation should be represented in 2- D) (4)
School of Chemistry Page 11 (iii) If the edge length is 564 pm, what is the density of NaCl in g cm -3. (4) (iv) Prove that the minimum radius ratio expected for the NaCl structure is 0.414. (4)
School of Chemistry Page 12 (b) Write the Born- Mayer equation. Use the equation to estimate the lattice energy of sodium chloride. (4) (N A = 6.022 x 10 23 mol -1, e = 1.602 x 10-19 C, d o = 282 pm, d = 34.5 pm, n = 8.174, ε o = 8.854 x 10-12 J -1 C 2 m -1, A = 1.748). [18]
QUESTION 6 School of Chemistry Page 13 (a) Classify the following Group 14 elements as metals, semi- metals and non- metals: (i) carbon (1) (ii) lead (1) (iii) silicon (1) (b) Write down the allotropes of tin (Sn). (3) (c) Use the trans effect series to suggest synthetic routes to both cis- and trans- [PtCl 2 (NH 3 )(PPh 3 )], using PPh 3, NH 3 and [PtCl 4 ] 2- as reactants. (6) [12]
QUESTION 7 School of Chemistry Page 14 (a) Complete the following: Mg 2 Si + 2 H 2 SO 4 (2) (b) Give an example of an organosilicon compound. Why are these compounds thermally stable and chemically inert? (2) (c) Give a general mechanism showing how paraffins are cracked at high temperatures using a zeolite such as HZSM-5 as the catalyst. (6) [10]