Analytical Chem istry - DePauw University

138 Analytical Chemistry 2.021. A 2.6540-g sample of an iron ore, known to be 53.51% w/w Fe, is dissolvedin a small portion of concentrated HCl and diluted to volume ina 250-mL volumetric flask. A spectrophotometric determination of theconcentration of Fe in this solution yields results of 5840, 5770, 5650,and 5660 ppm. Determine whether there is a significant differencebetween the experimental mean and the expected value at a = 0.05.22. Horvat and co-workers used atomic absorption spectroscopy to determinethe concentration of Hg in coal fly ash. 22 Of particular interestto the authors was developing an appropriate procedure for digestingsamples and releasing the Hg for analysis. As part of their study theytested several reagents for digesting samples. Results obtained usingHNO 3 and using a 1 + 3 mixture of HNO 3 and HCl are shown here.All concentrations are given as ng Hg/g sample.HNO 3 161 165 160 167 1661+3 HNO 3 –HCl 159 145 140 147 143 156Many of the problems that follow require accessto statistical tables. For your convenience,here are hyperlinks to the appendices containingthese tables.Appendix 3: Single-Sided Normal DistributionAppendix 4: Critical Values for the t-TestAppendix 5: Critical Values for the F-TestAppendix 6: Critical Values for Dixon’s Q-TestAppendix 7: Critical Values for Grubb’s TestDetermine whether there is a significant difference between these methodsat a = 0.05.23. Lord Rayleigh, John William Strutt (1842-1919), was one of the mostwell known scientists of the late nineteenth and early twentieth centuries,publishing over 440 papers and receiving the Nobel Prize in 1904for the discovery of argon. An important turning point in Rayleigh’sdiscovery of Ar was his experimental measurements of the density of N 2 .Rayleigh approached this experiment in two ways: first by taking atmosphericair and removing all O 2 and H 2 ; and second, by chemicallyproducing N 2 by decomposing nitrogen containing compounds (NO,N 2 O, and NH 4 NO 3 ) and again removing all O 2 and H 2 . Following arehis results for the density of N 2 , published in Proc. Roy. Soc. 1894, LV,340 (publication 210) (all values are for grams of gas at an equivalentvolume, pressure, and temperature). 23AtmosphericOrigin:ChemicalOrigin:2.31017 2.30986 2.31010 2.310012.31024 2.31010 2.310282.30143 2.29890 2.29816 2.301822.29869 2.29940 2.29849 2.29889Explain why this data led Rayleigh to look for, and discover Ar.24. Gács and Ferraroli reported a method for monitoring the concentrationof SO 2 in air. 24 They compared their method to the standard method byanalyzing urban air samples collected from a single location. Sampleswere collected by drawing air through a collection solution for 6 min.22 Horvat, M.; Lupsina, V.; Pihlar, B. Anal. Chim. Acta 1991, 243, 71–79.23 Larsen, R. D. J. Chem. Educ. 1990, 67, 925–928.24 Gács, I.; Ferraroli, R. Anal. Chim. Acta 1992, 269, 177 –185.