A0.4569 g sample of pewter, containing tin, lead, copper, and zinc, was dissolved in acid. tin was precipitated as sno2·4h2o and removed by filtration. the resulting filtrate and washings were diluted to a total volume of 250.0 ml. a 20.00 ml aliquot of this solution was buffered, and titration of the lead, copper, and zinc in solution required 34.02 ml of 0.001513 m edta. thiosulfate was used to mask the copper in a second 25.00 ml aliquot. titration of the lead and zinc in this aliquot required 34.42 ml of the edta solution. finally, cyanide was used to mask the copper and the zinc in a third 30.00 ml aliquot. titration of the lead in this aliquot required 25.92 ml of the edta solution. determine the percent composition by mass of each metal in the pewter sample.