help!

Jan 2019
2
0
wales
A 3.00 g sample of an alloy (containing only Pb and Sn) was dissolved in nitric acid (HNO3). Sulfuric acid was added to this solution, which precipitated 1.69 g of PbSO4 (RMM = 303.26 g/mol). Assuming that all of the lead (Atomic mass = 207.2 g/mol) was precipitated, what is the weight percentage of Sn in the sample?
 
May 2015
24
0
Houston, TX
Given 3.00-g sample of Alloy + Acid solution => 1.69-g PbSO₄ ppt.
Wt% Pb = (207.19/303.26)100% = 68.32 Wt% of PbSO₄ ppt wt.
Mass of Pb in ppt’d sample = 68.32% of 1.69-g = 0.6832(1.69-g) = 1.155-g Pb in ppt.
Mass of Sn in ppt’d sample = 1.69-g – 1.155-g = 0.5354-g Sn in ppt.
Wt% Sn in given sample = (0.5354/3.000)100% = 17.85 Wt%