This document contains chemistry problems involving calculating percentages of elements in compounds, determining empirical and molecular formulas, and identifying formulas of hydrates. It asks the student to find the percentage of oxygen in several compounds, calculate grams of oxygen in a given amount of compound, determine empirical formulas based on percentage composition, calculate molecular formulas given empirical formulas and molar masses, and write formulas for hydrates when given the masses of the anhydrous compound and water.