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UNIVERSITI TEKNOLOGI MARAFINAL EXAMINATION

COURSECOURSE CODEEXAMINATIONTIME

SPECTROCHEMICAL METHODSOFANALYSISCHM580APRIL2 113 HOURS

INSTRUCTIONSTOCANDIDATES1 . This question paper consistsofnine 9)questions.2. Answer ALL questionsin theAnsw er Booklet. Start each answ er ona newpage.3. Do not bring any material into the examination room unless permission is given by theinvigilator.4. Please chec ktomake sure that this examination pack consistsof:

i) theQuestion Paperii) anAnsw er Booklet- providedby theFacultyHi) aGraph Paper- providedby theFacultyiv) IR, NMR andMass Correlation Charts- providedby theFaculty

DO NOT TURNT ISP GEUNTILYOU RE TOLD TO O SOThis examination paper consistso 8 printed pages Hak Cipta Universiti Teknologi MARA C O N F ID E N T IA L

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QUESTION 1a) An argon ion laser operates at 496 .5 nm.

i) Wha t is the wavenu mbe r of the laser at 496. 5 nm?(1 m ark)

ii) W hat is its frequency? (1 m ark)b) Lasers are used as sources in many of the spectroscopic instruments. Identify ONEsuch method and indicate what analytical advantage the use of a laser contributed tothe method.

(2 marks)c) Sketch, label and state the functions of the components of a grating monochrom ator.Explain why monochromators are widely used in current spectrometers. (6 marks)

QUESTION 2a) Explain the differences betwee n the following agents used in atomic absorption andemission spectroscopy

i) releasing agentii) protective agentiii) ionization suppressor

(3 marks)b) W hy is source mod ulation emp loyed in atomic absorption spectroscopy? (2 marks)c) Inductively coupled argon plasm a emission intensities are typically linear withconcentration over a few orders of magnitude, whereas atomic absorptionmeasu rements are linear typically over a very limited range. Explain. (3 marks)

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d) Refer to the diagram below

i) Name the object shown in the diagram . Be specific. (1 m ark)ii) Explain the advantage o f the long slot. (2 marks)iii) How and where is the samp le introduced? Explain the processes which occur whenthe sample is introduced. (3 marks)iv) What is the potential danger associated with this part of the instrument? How can itbe dealt with? (2 marks)

QUESTION 3a) Describe standard addition and discuss why this calibration method should be employedin an analysis. W hat type of sample is standard addition m ethod preferably used?(3 marks)b) The data below are the detection limits of potassium and silver in ppb determined forFlame AAS, GFAAS and ICP-OES in a task of establishing the detection limits for thetwo elements using atomic spectroscopy. Clearly explain the trends in the data,including why the trends for the tw o elements are different.

ElementKAgFlame AAS10.9

GFAAS0.0040.001ICP-OES300.2

(4 m arks)

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QUESTION 4a) Draw a schematic diagram showing components of a single beam photometer forabsorption m easurements in the visible region. (4 m arks)b) Describe the m ajor advantages of double beam as comp ared to single beaminstruments for UV-visible absorbance measurements. (2 marks)c) A compou nd of formula weight of 280 g mol 1 absorbed 85.0% of the radiation at acertain wavelength in a 2.5 cm cell at a concentration of 15.0 ug ml_ 1. Calculate itsmolar absorptivity at the wavelength.

(3 marks)QUESTION 5a) i) Wh y is spectrophotometry less sensitive than spectrofluorometry? (2 marks)

ii) Explain why heterocyclic compounds such as furan as shown below do not exhibitf luorescence.

ofuran (2 marks)b) Fe2+ is determined spectrochemically by reacting with 1,10-phenanthroline to produce acomplex that absorbs strongly at 51 0 nm. A stock standard Fe2+ solution is prepa red bydissolving 0.0704 g ferrous ammonium sulphate, Fe(NH 4)2S04.6H20 (392.14 g mol 1), inwater in a 1 000 ml_ volumetric flask, adding 2.5 mL H 2S0 4 and diluting to mark. Aseries of working standards is prepared by transferring 1.00, 2.00, 5.00 and 10.00 mLaliquots of the stock solution to separate 100 mL volumetric flasks and addinghydroxylammonium chloride solution to reduce any Fe3+ to Fe2+ , followed by

phenanthroline solution and then dilution to volume with water. An un known sample isprepared by adding the same amount of reagents in a 100 mL volumetric flask anddiluting to volum e. If the following absorban ce readings measured against blank areobtained at 51 0 n m, calculate the molar concentration of the unknow n sam ple.(8 marks)

SolutionStandard 1Standard 2Standard 3Standard 4Sample

A0.0810.1710.4320.8570.482(8 marks)

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QUESTION 6a) The most common detector used in FTIR is TGS (Triglycine sulfate) detector which is atherm al detector. Explain why a photon detector cannot be used in FTIR spectrometer.(3 marks)b) Explain why a FTIR spectrometer will give spectra having a better signal-to-noise ratiothan a dispersive IR spectrometer. (2 marks)c) IR spectra and Raman spectra can give information about the same vibrational energytransitions in a molecule.

i) Describe and sketch an energy diagram to show the transitions and processes thatare im portant in vibrational spectroscopy. (6 marks)ii) For a particular vibrational change, what requirements mus t be met in order toobserve an IR absorption and a Raman shift? (4 marks)

QUESTION 7a) Describe how to distinguish between propanone, pentane-2-one and pentane-3-one bymass spectrometry. Explain using fragmentation of each. (6 marks)b) Calculate the m/z and relative abundance (intensity) for the M + and (M+ + 1) peaks for2-chloropropane. Assum e the molecular ion to be the base peak in each case. (3 marks)c) State the advantages and disadvantages of an electron impact source. (3 marks)d) Give two applications of molecular mass spectrometry.

(2 marks)QUESTION 8a) Why a superconducting magnet is used in a high resolution NMR spectrometer? (1 mark)b) What type of solvents is used in NMR? W hy? (1 mark)

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c) W hat are the purposes of locking and shimming in a NMR op eration?

d) i) What is meant by 'chemical equivalence' in NMR?(2 marks)

(1 mark)ii) C3H6CI2gives onlyONEsignal in its 1HNMR spectrum . Propose the structural formula.(3 marks)

QUESTION 9The IR, mass, 1H NMR and 13C NMR spectra shown below are for a compound with theformula of C 7H 1 40 2 . Wh at is the structure of the compound? Justify your answer. (9 marks)

IR spectrum

HfNENWIBEHl il

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Mass spectrum

1 H NMR spectrum

11 ] ' r10 9

Doublet, J= 6

Quartet,J=1 .

Doublet,J= 2.0

HSP-00-116 ppm

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13 C NMR spectrum

200CDS-03-419 ppm

END OF QUESTION PAPER

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