Introduction: Chemists are often interested in obtaining a certain mass of product from a chemical reaction without wasting any reactants. But how is this done? To calculate the masses of reactants needed for a desired
mass of product, it is necessary to understand a unit of quantity called the mole.
Question: How do chemists know how much of each substance to mix?
1. Observe: The mass of a molecule of a substance is its molecular mass (M). Molecular mass is measured in
universal mass units (u). One universal mass unit (1 u) is approximately the mass of a proton. Hydrogen gas
has a molecular mass of 2.0158 u.
A. Type the formula "H2" into the Reactants box. What is the molar mass of hydrogen gas, H,?
B. What is the relationship between the molecular mass and the molar mass of a substance?