An analytical chemist decides toanalyze a given sample spectrophotometrically for its coppercontent.  The chemist knows that copper(I) ions form acolored coordination complex with neocuproine (ncup),C14H12N2, in a one-to-two ratio,Cu(ncup)2+.  The chemist also knowsthat Cu(ncup)2+ is more soluble in3-methyl-1-butanol than in water and thatCu(ncup)2+ in 3-methyl-1-butanol shows anabsorbance maximum at 454 nm.  Thus, the chemist proceedswith the chemical analysis.  She treats 0.1482 g ofcopper wire, 98.50% (w/w) pure, with a minimum volume ofconcentrated nitric acid in order to get all of the copper metalinto solution (aqueous) as copper (II) ions.  Afterneutralizing the copper-containing solution with base, the chemisttransfers the solution quantitatively to a 500.0-mL volumetricflask and then dilutes the solution with deionized water up to themark on the flask.  Next, the chemist treats 10.00 mL ofthe solution with a reducing agent in order to convert copper(II)ions to copper(I) ions and then adds a buffer in order to changethe pH of the solution to one for which complexation betweencopper(I) ions and neocuproine occursreadily.  Subsequently, the chemist treats the resultingsolution with neocuproine to complex all of the copper(I) ions andthen adds 100.00 mL of 3-methyl-1-butanol.  After shakingwell to make sure that essentially all of theCu(ncup)2+ is extracted by the3-methyl-1-butanol from the aqueous solution, the chemist separatesthe aqueous layer (bottom) completely from the 3-methyl-1-butanollayer (top) and then quantitatively transfers the3-methyl-1-butanol layer to a 1.000-L volumetric flask, dilutingthe solution with 3-methyl-1-butanol up to the mark on theflask.  Using a spectrophotometer, the chemist finds thepercent transmittance of the final 3-methyl-1-butanol solution in a2.00-cm cuvet is 18.8 at 454 nm.  The chemist thenprepares the sample.  She treats 0.2990 g of thepreviously dried copper oxide sample with a minimum volume ofconcentrated sulfuric acid in order to get all of the copper intosolution (aqueous) as copper(II) ions.  Afterneutralizing the copper-containing solution with base, the chemisttransfers the solution quantitatively to a 500.0-mL volumetricflask and then dilutes the solution with deionized water up to themark on the flask.  Next, the chemist treats 10.00 mL ofthe solution with the reducing agent and then adds thebuffer.  Subsequently, the chemist treats the resultingsolution with neocuproine and then adds 100.00 mL of3-methyl-1-butanol.  After shaking well to make sure thatessentially all of the Cu(ncup)2+ isextracted by the 3-methyl-1-butanol from the aqueous solution, thechemist separates the aqueous layer (bottom) completely from the3-methyl-1-butanol layer (top) and then quantitatively transfersthe 3-methyl-1-butanol layer to a 500.0-mL volumetric flask,diluting the solution with 3-methyl-1-butanol up to the mark on theflask.  Using a spectrophotometer, the chemist finds thepercent transmittance of the final 3-methyl-1-butanol solution in a2.00-cm cuvet is 27.6 at 454 nm.  Find the percent bymass of copper in the sample analyzed by the analyticalchemist.
