Question

Teaspoons made from a certain alloy containing the elements bismuth, lead, tin and indium are not recommended for stirring sugar into hot coffee, as the alloy melts at 58 °C.

A sample of the alloy, weighing 5.038 g, was treated in such a way as to convert the tin to 0.742 g SnO2, the lead to 1.298 g PbSO4 and the bismuth to 2.780 g Bi2O3.

What is the percentage, by mass, of each of the four elements in the alloy sample?

Answer 1

i) SnO2 to Sn conversion factor = mass of one mole of Sn/ mass of mole of SnO2 = 118.71g/150.71g = 0.78767

mass of Sn in the sample = 0.78767× 0.742g = 0.5845g

℅ of Sn in the alloy = (0.5845g/5.038g)×100 = 11.60%

ii) PbSO4 to Pb conversion factor = mass of one mole of Pb/mass of one mole of PbSO4 = 207.2g/303.265g = 0.6832

mass of Pb in sample = 0.6832× 1.298g = 0.8868g

% of Pb in sample = (0.8868g/5.038g)×100 = 17.60%

iii) Bi to Bi2O3 conversion factor = 417.96g/465.96g = 0.8969

mass of Bi in sample = 0.8969 × 2.780g = 2.4933g

% of Bi in Bi2O3 =(2.4933g/5.038)×100 = 49.49%