Ambo UniversityDepartment of ChemistryChem. 572 Advanced Instrumental AnalysesInstrumentation and interpretation of spectraExercises in spectroscopic techniques1. A 15.0m! sample of a compound "ith a molecular mass of #$%. "as dissolved in a 5m' volumetric flas(. A 1.00m' ali)uot "as "ithdra"n* placed in a 10m' volumetricflas(* and diluted to the mar(. +hen 10m' sample "as placed in a 0.500cm cuvet and!ave an absorbance of 0.% at %,5 nm. -ind the molar absorptivity ./%,5* "ith units of 0

1.cm11 at this "avelen!thAns. 01 2 n3v.'1 2 153.#$%. 2 0.007$ mol3' and 0151 2 0252*02 2 140.007$310 20.0007$ mol*/ 2 A3cb 2 0.%3.0.0007$40.51 2 1&25.&%01cm12. Durin! an assay of the thiamine .vitamin 611 content of a pharmaceutical preparation* thepercent transmittance scale "as accidentally read* instead of the absorbance scale of thespectrophotometer. 7ne sample !ave a readin! of $2.28 T* and a second sample !ave areadin!of 50.78 Tat a"avelen!thof ma9imumabsorbance. :hat is theratioofconcentrations of thiamine in the t"o samples;Ans. A1 2 /c1b 2log T1 2 2log %T1 and A2 2 /c2b 2log T2 2 2log %T2C1< C2 2 .2log 82.213.2log 50.71 2 0.2$$#. A1.2$=10>%0solutionof potassiumperman!anatehas atransmittanceof 0.5"henmeasured in a 1 cm cell at 525 nm.1. Calculate the molar absorptivity coefficient for the perman!anate at this"avelen!th.2. If theconcentrationis doubled"hat "ouldbetheabsorbanceandthepercenta!etransmittance of the ne" solution;%. A polluted "ater sample contains appro9imately 0.1 ppm of chromium* .0 2 52 ! mol>11.+he determination for Cr.5I1 based upon absorption by its diphenylcarba?ide comple9.ma92 5%0nm* ma92 %1 700 'mol>1 cm>11 "as selected for measurin! the presence of themetal. :hat optimum pathlen!th of cell "ould be re)uired for a recorded absorbance ofthe order of 0.%;5. @aints and varnishes for use on e9teriors of buildin!s must be protected from the effectsof solar radiation"hichaccelerate their de!radation.photolysis andphotochemicalreactions1.Aiventhat< 0 2 500! mol>1B Cma92 15000 'mol>1 cm>1for Cma92#50nm* "hat must be the concentration .e9pressed in !'>11 of a U5 additive 0 such that,08 of the radiation is absorbed by a coatin! of thic(ness 0.# mm;&. @yridine* a commonlaboratorycompoundthat is (no"ntocause sterilityinmen*e9hibits a U5 transition at ma9 270 nm. :hen pyridine is reacted "ith dilute DCl* thisabsorption band !oes a"ay. E9plain this phenomenon usin! pictures and "ords. Does thisdatae9plain"hat type of transitionis occurrin!intheU5absorptionspectrumofpyridine at 270 nm;7. 6yemployin!the empirical rules of :ood"ardF-ieser* predict the positionof thema9imum absorption of the compounds "hose structures are seen belo"$. If chloroform .trichloromethane1 e9hibits an infrared pea( at #01$cm>1 due to the CFDstretchin! vibration* calculate the "avenumber of the absorption band correspondin! tothe CFD stretchin! vibration in deuterochloroform .e9perimental value 225#cm>11.,. +odeterminetheconcentrations.mol3'1ofCo.G7#12.A1andCr.G7#1#.61inanun(no"n sample* the follo"in! representative absorbance data "ere obtained.0easurements "ere made in 1.0 cm !lass cells.1. Calculate the four molar absorptivities< A.5101* A.5751* 6.5101 and 6.5751.2. Calculate the molarities of the t"o salts A and 6 in the un(no"n.10. If + 2#00H* calculate the ratio of the populations GE13GE2 for a proton in an G0Ispectrometer "here the applied ma!netic field 6 2 1C%+. 0a(e the same calculation forthe case "here the field 627+* !iven that 22.&752=10$ rad +>1 s>1.11. 1. Calculatethechemical shift* J* inppmof aproton.1D1* "hoseG0Isi!nal isdisplaced by 220 D? "ith respect to +0K .the field of the spectrometer is 1.$7, +1. 2. +he resonance si!nal for a proton is displaced by ,0 D? "ith respect to +0K "henmeasuredona&00D?spectrometer.:hat "ouldhappentothisdisplacement ifanapparatus of 200 0D? "as employed; #. :hat "ould be the correspondin! chemical shift of the same proton"ith both of thesespectrometers;12. Kpectrophotometric analysis of phosphate can be performed by the follo"in!procedure< Standard A. HD2@7%.-0 1#&.0,1< $1.#7 m! dissolved in 500.0 m' of "atersolutions6. Ga20o7% . 2D27 .sodium molybdate1< 1.25 ! in 50 m' of 5 0 D2K7% C. D#GGD2L # K72 % .hydra?ine sulfate1< 0.15 ! in 100 m' of D27 Procedure @lace the sample .either an un(no"n or the standard phosphate solution* A1 ina 5m' volumetric flas(* and add 0.500 m' of 6 plus 0.200 m' of C. Dilute to almost 5m' "ith "ater* and heat at 100MC for 10 minutes to form a blue product.D#@7%.0o7#112* 12 molybdophosphoricacid1. Cool theflas(toroomtemperature*dilute to the mar( "ith "ater* mi9 "ell* and measure the absorbance at $#0 nm in a 1.00cm cell..a1 :hen 0.1%0 m' of solution A "as analy?ed* an absorbance of 0.$2, "as recorded. Ablan(carriedthrou!hthesameprocedure!aveanabsorbanceof0.017. -indthemolar absorptivity of blue product. .b1 A solution of the phosphatecontainin! ironstora!e protein ferritin "as analy?ed bythis procedure. +he un(no"n contained 1.#5 m! of ferritin* "hich "as di!ested in atotal volume of 1.00 m' to release phosphate from the protein. +hen 0.#00 m' of thissolution "as analy?ed by the procedure above and found to !ive an absorbance of0.$#&. A blan( carried throu!h this procedure !ave an absorbance of 0.0#$. -ind the"ei!ht percent of phosphorus in the ferritin.1#. Nou are a supervisor in a laboratory "hich focuses on the determination of trace andultratrace levels of to9ic substances in "ater samples. Usually* for the determination of@bin"ater*aAraphite-urnace Atomic AbsorptionKpectrophotometer.A-AAK1isusedbut* sinceit "asdo"nfor repairs* oneof thetechniciansthat yousupervisedecided to use the operable -lame AAK instrument. After establishin! that absorbancevariedlinearly"iththeamount of @b* thefollo"in!absorbancevaluedata.for 5replicatemeasurements1 "ereobtainedforablan(andfor asamplesubmittedforanalysis< submitted for analysis