Question

The percentage of sulfur in coal can be determined by burning a sample of the solid and passing the resulting sulfur dioxide gas into a solution of hydrogen peroxide, which oxidizes it to sulfuric acid, and then titrating the acid. Calculate the mass percent of sulfur in a sample if the gas from an 8.05-g sample required 44.1 mL of 0.114 M NaOH in the titration of the diprotic acid.

Answer 1

The reactions are,

S + O2 ---> SO2

SO2 + H2O2 ----> H2SO4

H2SO4 + 2NaOH ----> Na2SO4 + 2H2O

Given,

Mass of sample = 8.05 g

According to the 3rd reaction, 1 mole of H2SO4 will need 2 moles of NaOH

Moles of NaOH = Molarity x Volume (L)

=> Moles of NaOH = 0.114 x 0.0441 = 0.0050274 moles

=> Moles of H2SO4 = 0.0050274 / 2 = 0.0025137 moles

=> Moles of S (sulfur) = 0.0025137

Atomic Mass of S = 32.065 g / mol

=> Mass of S = 0.0025137 x 32.065 = 0.081 g

=> Mass % of S in sample = (0.081 / 8.05) x 100 = 1.001 %