About MOLECULAR WEIGHTS

Molecular Weight or its related value, Equivalent Weight, Formula Weight or Empirical Formula Weight is an important fundamental property of each molecule.

How many ways are there to determine a Molecular, Equivalent or Empirical Formula Weight? How many methods have you actually used?

Here is a partial list of methods. You have used almost all of these in this course (General Chemistry Laboratory, Chem 113-114). You should recognize all of them and may even come up with an additional few of the many, many more.

1. Colligative Properties
   • Freezing point depression
   • also Boiling point elevation and Osmotic pressure (not studied)
2. Elemental Analysis
   • Determine the empirical formula and calculate empirical formula weight from Atomic Weights in Hydrates
3. Gas Laws
   • Dumas method, measuring the density of a gas
   • Measuring volume of gas generated in a reaction
   • also Gaseous Diffusion (not studied)
4. Solution Stoichiometry
   • Weight of acid and volume and molarity of base needed to neutralize it in pH and BUFFERS as well as the LAB PRACTICAL
   • Amount of reagent used to react with a given mass of reactant
5. Calorimetry
   • Rule of Dulong and Petit... Molar heat capacity is approximately 25 j/mol/° C for Avogadro's number of particles

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