Analytical Chem istry - DePauw University

402 Analytical Chemistry 2.032. The iron in an organometallic compound was determined by treatinga 0.4873-g sample with HNO 3 and heating to volatilize the organicmaterial. After ignition, the residue of Fe 2 O 3 weighed 0.2091 g.(a) What is the %w/w Fe in this compound?(b) The carbon and hydrogen in a second sample of the compoundwere determined by a combustion analysis. When a 0.5123-g samplewas carried through the analysis, 1.2119 g of CO 2 and 0.2482g of H 2 O were collected. What are the %w/w C and %w/w H inthis compound and what is the compound’s empirical formula?33. A polymer’s ash content is determined by placing a weighed sample in aPt crucible that has been previously brought to a constant weight. Thepolymer is melted under gentle heating from a Bunsen burner untilthe volatile vapor ignites. The polymer is allowed to burn until only anon-combustible residue remains. The residue is brought to constantweight at 800 o C in a muffle furnace. The following data were collectedduring the analysis of two samples of a polymer resin.Polymer A g crucible g crucible + polymer g crucible + ashreplicate 1 19.1458 21.2287 19.7717replicate 2 15.9193 17.9522 16.5310replicate 3 15.6992 17.6660 16.2909Polymer B g crucible g crucible + polymer g crucible + ashreplicate 1 19.1457 21.0693 19.7187replicate 2 15.6991 12.8273 16.3327replicate 3 15.9196 17.9037 16.5110(a) For each polymer, determine the mean and the standard deviationfor the %w/w ash.(b) Is there any evidence at a = 0.05 for a significant difference betweenthe two polymers? See the appendices for statistical tables.34. In the presence of water vapor the surface of zirconia, ZrO 2 , chemicallyadsorbs H 2 O, forming surface hydroxyls, ZrOH (additional water isphysically adsorbed as H 2 O). When heated above 200 o C, the surfacehydroxyls convert to H 2 O(g), releasing one molecule of water for everytwo surface hydroxyls. Below 200 o C only physically absorbed water islost. Nawrocki, et al. used thermogravimetry to determine the densityof surface hydroxyls on a sample of zirconia that was heated to 700 o Cand cooled in a desiccator containing humid N 2 . 15 Heating the samplefrom 200 o C to 900 o C released 0.006 g of H 2 O for every gram of dehydroxylatedZrO 2 . Given that the zirconia had a surface area of 33 m 2 /g15 Nawrocki, J.; Carr, P. W.; Annen, M. J.; Froelicher, S. Anal. Chim. Acta 1996, 327, 261–266.