Chapter 5, Problem 125RQ

An organic compound contains carbon, hydrogen, and sulfur. A sample of it with a mass of 1.045 g was burned in oxygen to give gaseous ${\text{CO}}_{\text{2}}{\text{, H}}_{\text{2}}{\text{O, and SO}}_{\text{2}}$. These gases were passed through 500.0 mL of an acidified 0.0200 M ${\text{KMnO}}_{\text{4}}$ solution, which caused the ${\text{SO}}_{\text{2}}$ to be oxidized to ${\text{SO}}_{\text{4}}{}^{\text{2-}}$. Only part of the available ${\text{KMnO}}_{\text{4}}$ was reduced to ${\text{Mn}}^{\text{2+}}$. Next, 50.00 mL of 0.0300 M ${\text{SnCl}}_{\text{2}}$ was added to a 50.00 mL portion of this solution, which still contained unreduced ${\text{KMnO}}_{\text{4}}$. There was more than enough added ${\text{SnCl}}_{\text{2}}$ to cause all of the remaining ${\text{MnO}}_{\text{4}}{}^{\text{-}}$ in the 50 mL portion to be reduced to ${\text{Mn}}^{\text{2+}}$. The excess ${\text{Sn}}^{\text{2+}}$ that still remained after the reaction was then titrated with 0.0100 M ${\text{KMnO}}_{\text{4}}$, requiring 27.28 ml. of the ${\text{KMnO}}_{\text{4}}$ solution to reach the end point. What was the percentage of sulfur in the original sample of the organic compound that had been burned?