Hydrogen sulfide is composed of two elements, hydrogen and sulfur. In an experiment, 5.485 g of hydrogen sulfide is fully decomposed into its elements. How many grams of sulfur must be obtained if 0.307 grams of hydrogen are obtained?

To solve, apply conservation of mass. It states that in a chemical reaction, mass is neither destroyed nor created. So the mass of the reactants at the beginning is equal to the mass of the products at the end of the reaction.
mass of  reactants = mass of products
In this problem, the chemical reaction is:
Hydrogen sulfide -> Hydrogen  + Sulfur
Applying conservation of mass, the equation is:
mass of hydrogen sulfide = mass of hydrogen + mass of sulfur
5.485g = 0.307g + mass of sulfur
mass of sulfur = 5.485g - 0.307g
mass of sulfur = 5.178g
 
Therefore, at the end of the reaction, 5.178 grams of sulfur is obtained.