This study source was downloaded by 100000824210446 from CourseHero com on 01 01 2022 10 29 48 GMT 06 00 https www coursehero com file 29393969 Experiment 4 chm260docx EXPERIMENT 4 Flame Atomic Absorption Spectroscopy AAS OBJECTIVES1 To learn how to operate a flame AAS instrument 2 To plot a standard calibration curve for determination of Ca in sample 3 To determine the amount of Ca in a sample using the standard calibrationcurve INTRODUCTION Atomic Absorption Spectroscopy is an analytical laboratory technique that convertsthe analyte of study into a gaseous state for quantitative determination of chemicalspecies using the Beer Lambert Law AAS relies on the quantum principle that theground state energy of an atom absorb a discrete amount of electromagneticradiation before it is excited to a higher state energy This radiation is absorbed in theform of a wavelength with each element corresponding to its own wavelength thusgiving AAS a great degree of selectivity This is done by exciting the free atoms viaoptical radiation using a special hollow cathode lamp containing the interest allowingfor the precision required for the excitation wavelength Another advantage of usingAAS is it s easy use and relatively inexpensive cost when compared to other types ofhigh precision spectroscopy However AAS also contains its disadvantages SinceAAS relies on the nebulization of the analyte only solutions can be analyzed Inaddition AAS has less sensitivity than a graphite furnace which allows for analysis ofsmaller samples between 5 60 L whereas AAS requires samples in the range of 1 3mL2 AAS can only be used for quantitative analysis of an element whereas atomicemission or atomic fluorescence are quantitative and qualitative instruments APPARATUS Beaker Burette Retort stand Dropper This study source was downloaded by 100000824210446 from CourseHero com on 01 01 2022 10 29 48 GMT 06 00 https www coursehero com file 29393969 Experiment 4 chm260docx Volumetric flask 50mL CHEMICALS Deionized water 1000ppm Ca stock solutionPROCEDURE A Preparation of Standard Solutions1 5 0mL of 100ppm solution was pipetted Then was transferred to 50 0mLvolumetric flask and diluted with ionized water until the mark The solutionwas labelled as 100ppm 2 The 100ppm solution and a 50mL volumetric flask were used to preparethe series of standard solutions having the following concentrations 1ppm 3ppm 5ppm 7ppm and 9ppm 3 The unknown solution was obtained 4 The absorbance of the standard solutions in 2 followed by the unknownwere measured B Operation of the AASHow to run the AAS 1 The air compressor stock cock air acetylene regulator and acetylene tankwere opened 2 The compress air must be between 5 6kg cm 1 and the acetylene pressureis 100kPa 3 The exhaust fan was switched on 4 The isolating switch was switched on 5 The aspiration hose was make sure in the water or blank unless thesamples were running 6 The instrument was switched on 7 Switch on the computer 8 WinLab32 was double clicked wait until the calibrating equipment wasready 9 Click file new method starting condition Element Ca to createmethod 10 Method Editor untitled The Date was typed in Method description to determine the concentration of Ca Calibration equation linear through zeroChange unit for standards and unknown 11 Standard concentrationBlank DI water Standard Std1 Std2 Std3 Std4 and Std5 Concentration 1ppm 3ppm 5ppm 7ppm and 9ppm 12 File save as method This study source was downloaded by 100000824210446 from CourseHero com on 01 01 2022 10 29 48 GMT 06 00 https www coursehero com file 29393969 Experiment 4 chm260docx Name Method 13 File new sample info file OKSample ID unknown Ca14 File save as sample info File name save 15 Workspace was clicked whatever in the box was highlighted open type in your name 16 Burner switch was clicked analyzed standard analyse blank analyse sample unknown 17 The burner was switched off 18 Tool was clicked edit calibration 19 To print click file active window preview 20 To open the file for future references click file open workspace Filename ok analyse Recall Calibration DATA Table 4 1 Table of Added Volume and Concentration of Diluted StandardSolutionVolume of AddedStandard mLConcentration of AddedStandard ppm10 5121 5332 5543 5754 59Unknown number 1 Name of element CaConcentration of unknown 3 914mg L This study source was downloaded by 100000824210446 from CourseHero com on 01 01 2022 10 29 48 GMT 06 00 https www coursehero com file 29393969 Experiment 4 chm260docx QUESTIONS In a standard addition method you will prepare a series of solutions in which youadd different increments of standard solutions to fixed aliquots of an unknownsample X i e 10 0mL of X All solutions were prepared using 50 00mL volumetricflasks Suppose that the analysis of standard solutions of X gave the followingresults Solution Concentration of AddedStandard ppmAbsorbance Standard 10 000 201Standard 22 440 292Standard 34 880 378Standard 47 320 467Standard 59 760 5541 Plot the standard addition graph2 Determine the concentration of X in ppm in the unknown sample CO Csa Vflask Vunknown 6 0 ppm 50 00mL 10 00mL 6 00ppm 5 30 ppm DISCUSSION In the experiment the standard calcium solution was prepared and dilutions aremade to prepare solutions of 1 3 5 7 and 9 ppm of calcium Each solution isaspirated into the flame of the AAS and its absorbance measured From these data a calibration curve of absorbance versus ppm of calcium was plotted Then theunknown calcium solution that was prepared by lab assistance was aspirated intothe flame and its absorbance was determined The ppm of calcium in the dilutedunknown solution is read from the calibration curve which is 3 914mg L During theexperiment there were several precautions that should be prevented in order tominimize errors For example when diluting the solution of Calcium to 1 3 5 7 and 9ppm of Ca it has to dilute with distilled water In the volumetric flask the solution ofCa needed were poured and distilled water was added The distilled water must beadded until the calibration mark If distilled water was exceeded the calibration mark it will affect the concentration of the solution This study source was downloaded by 100000824210446 from CourseHero com on 01 01 2022 10 29 48 GMT 06 00 https www coursehero com file 29393969 Experiment 4 chm260docx CONCLUSION In the end of the experiment we had learned how to operate a flame AAS instrumentand also know how to plot a standard calibration curve for determination of