Question

Antimony is alloyed with lead to increase the rigidity of components used in the construction of lead storage batteries.
2.606 g of a particular metallic alloy, compounded of only Pb and Sb, can be quantitatively converted into a 3.034-g mixture of the oxides PbO₂ and Sb₂O₄.
What was the percentage (by mass) of antimony in the alloy?

Answer 1

Let z be the mass (in grams) of Pb in the alloy.
Then mass of Sb in the alloy will be (2.606-z )

[z / (207.21 g Pb/mol) ] x (1 mol PbO₂ / 1 mol Pb) x (239.1988 PbO₂/mol) = 1.15438 z g PbO

[(2.606-z) / (121.760 g Sb/mol)] x (1 mol Sb₂O₄ / 2 mol Sb) x (307.5176 g Sb₂O₄/mol) = (3.29086 - 1.2628 z) g Sb₂O₄
Now,

(1.15438 z) + (3.29086 - 1.2628 z) = 3.034
=> -0.10842 z = - 0.25686

=> z = 0.25686 /0.10842

=> z =2.3691 g Pb
Again,

2.606 g total - 2.3691 g Pb = 0.2369 g Sb

Finally, thepercentage (by mass) of antimony(Sb) in the alloy will be---

(0.2369 g Sb) / (2.606 g total) x 100 %= 0.0909056 x 100 % = 9.09 % Sb by mass