Question

A 1.27g sample of galena, a mineral of lead and sulfur, is found to contain 1.10g of lead. How many grams of sulfur does another sample of galena, with a mass of 3.85g contain?

Answer 1

sample mass = 1.27g

lead mass = 1.1 g

moles of lead = mass of lead / atomic mass of lead = 1.1g / ( 207.2g/mol) = 0.0053 mol

sulphur mass = 1.27 - 1.1 = 0.17 g

sulphur moles = ( 0.17g) / ( 32.065 g/mol) = 0.0053 mol

Thus lead and sulphur are present in equal moles

Now galena mass = 3.85 g

let sulphur moles = lead moles = m

Sulphur mass = moles x atomic mass of sulphur = m x 32.065 g/mol = 32.065 m

lead moles = m x 207.2 g/mol = 207.2 m

Sample mass = lead + sulphur mass

3.85 = 207.2m + 32.065m

m = 0.016

Thus sulphur mass = 32.065 g/mol x 0.016 mol = 0.516 g