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CONFIDENTIAL AS/OCT 2010/CHM580

UNIVERSITI TEKNOLOGI MARAFINAL EXAMINATION

COURSECOURSE CODEEXAMINATIONTIME

SPECTROCHEMICAL METHODS OF ANA LYSISCHM580OCTOBER 20103 HOURS

INSTRUCTIONS TO CANDIDATES1 . This question paper consists of two (2) parts : PART A (3 Questions)PART B (3 Questions)2. Answer ALL questions from PART A and PART B into two (2) different Answer Booklets.Start each answer on a new page.3. Do not bring any ma terial into the examination room unless permission is given by theinvigilator.4. Please check to ma ke sure that this examination pack consists o f:

i) the Ques tion Paperii) an Ans wer Booklet - provided by the Facultyiii) a Graph Paper - provided by the Facultyiv) an Uv-vis/NM R/IR table - provided by the Faculty

DO NOT TURNT ISP GE UNTIL YOU RE TOLD TO DO SOhis examination paper consists of printed pages

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CONFIDENTIAL 2 AS/OCT2010/CHM580

PART A

QUESTION 1a) Briefly define the following terms:i) absorptionii) spectrophotometeriii) Bee r's law (3 marks)b) In hexane, acetone has an absorption maximum at 270 n m, where its molar absorptivityhas a value of 12 M 1 cm 1 . Our spectrometer can reliably measure transmittancebetween 10% and 90%. What is the range of acetone concentration that can bemeasured in a1.00 cmcell under these circumstances? (5 marks)c) Sketch and describe the instrum ental com ponents of an ultraviolet-visiblespectrophotometer. Outline the physical principles behind its operation and specify anylimitations to its operation. (8 marks)d) Explain and relate the following terms below as used in the ultraviolet-visiblespectroscopy:

i) Bathochrom ic shiftii) Hypsoch romic shiftiii) Auxochrome (3 marks)e) A s pectrophotometric assay was undertaken with a substance with a molar absorptivityof 4000 M 1cm 1 . A stock solution is available whose concentration is 0.0195 M. Theinstrumental path length is 1 .000 cm. A final absorbance in the range between 0.4 - 0.5is desired to calibrate in the range of the unknown solutions. You are to make up 500.0mL of the calibration solution in a volumetric flask. Do you need to pipette 1.00, 2.00,3.00, 4.00 or 5.00 mL of the stock solution into the 500.0 mL volum etric flask to provide a

solution in this absorban ce range? Show your wo rk. (4 marks)f) Arrange the following transitions from the highest energy transition to the lowest energytransition?

n -> a , n -> n ,a - a ,n->n (1 m ark)

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CONFIDENTIAL 3 AS/OCT2010/CHM580

QUESTION 2a) Briefly define the follow ing terms :i) dipole mom entii) interferogramiii) Michelson interferometer (3 marks)b) Predict the most suitable compou nd, with the given the molecular formula C 7H 60 2 thatcan fit the IR and NMR spectra below. (The peak near 80 ppm in the 13C spectrum is thesolvent.)

Infrared Spectrum

3

3500 3000 2500 2000Wavenumber ( cm-1 )

1500 1

13C NMR Spectrum

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CONFIDENTIAL 4 AS/OCT 2010/CHM580

s i T^D r h r h T^D n h BG sis ^ d rNMR Spectrum

H(exchanges)

1H

2H2H

_K_i.

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c) Explain the physical phenomen a of the Raman effect. (5 marks)

QUESTION 3a) Briefly define the following terms as used in nuclear magnetic resonance spectroscopy:i) coupling constantii) chemica l shift (2 marks)b) Draw a block diagram of an NMR spectrometer. Label each compon ent com pletely.(4 m arks)

c) Predict a tentative peak assignme nt of 1HNMR and 1 3CNMR spectra for benzaldehyde .(For full credit be sure to label each signal clearly and assign the chemical shift of eachpeak.) (8 marks)

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PARTB

QUESTION 1a) Describe the principles of Atom ic Emission Spectrometry (AES) and of AtomicAbsorption Spectrometry (AAS). Include in your discussion the mechanism of obtainingthe atomic vapou r and how the signals obtained in each technique is related to theamount of analyte in the samples analyzed. (8 marks)b) Explain why electrothermal atomizers result in greatly enhanced sensitivity comparedto f lame AAS. (4 m arks)c) An analyst notes that a 1 ppm solution of sodium gives a flame AAS signal of 1 10, whilethe same solution containing 20 ppm solution of potassium gives a signal of 125. It wasobserved that a 20 ppm solution of potassium exhibit no blank reading. Explain theobserved results. (4 marks)d) State and briefly describe two methods of sample introduction in an inductively coupledplasma. W hich of the two methods can be used to introduce solid samples? (5 marks)e) Calcium in a sam ple solution is determined by Inductively Coup led Plasma (ICP-AES).A stock solution of calcium is prepared by dissolving 1.50 g CaCI 2 .2H 20 in deionizedwater and diluting it to 1 .00 L. Wo rking standards are prepared by diluting the standardsolution as sho wn in the table below, with the final volume of each being 1 00.00 mL.

Standard Volume(mL)0.005.0010.0015.0020.00Sample

Intensity0.00000.23800.42200.59990.81200.6280

i) Calculate the conc entration of each working standards in the table in units of partsper million (pp m). (2 marks)ii) Determine the concentration of calcium in the original sample if the sam ple intensityreading in the table abo ve was ob tained by taking 5.00 mL of the original sample a nddiluting it to 2 5.00 mL solution. (5 marks)

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QUESTION 2a) Com pare and contrast the design and optical comp onents of a single beam ultravioletvisible (UV-Vis) absorption spectrophotometer and fluorescence spectrophotometer. Inyour discussion include the differences observed and explain why these differences arenecessary. (8 marks)b) The relative fluorescen ce intensity at a wave length of 228.8 nm of a 1 2.5 x 10 5 Mcadmium chloride solution was measured to be 75.4. What is the concentration of acadmium chloride solution with a measured intensity of 50.5? (3 marks)c) Rank the following comp ounds in order of highest to lowest quantum efficiency (OF) andexplain your answers.Indicate if you think the com pound does not fluoresce (OF = 0).

(0

(v) (4 marks)

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QUESTION 3a) Briefly explain the principle used in an electron impact ion source and state oneadvantage and one disadvantage of this source. (4 marks)b) How could the following isomers be differentiated by mass spectrometry?

C H 3 _ C H 2 - C H 2 - C H C H 3 andOH

END OF QUESTION PAPER

C H 3CH3 C CH 2 _Cr i3

O H(5 marks)

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CHM580 (3)

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