Chemistry 11
Unit 5: The Mole Concept
Name:____________________
Date:______________Bl:____
Learning Goal: To understand the relationship between mass, number and type of particles, volume, and
concentration for any chemical.
Concept 6: Finding the Molecular Formula of a Pure Substance
Empirical vs. Molecular
_______________ is the smallest _______________ of a molecule while _______________ is always some
multiple of the empirical formula to reflect the actual compound structure.
So… Which of the following are empirical formulae? Which are molecular formulae?
Pure Substance
Empirical or Molecular?
C12H24
C100H200
CH2
C26H52
C3H6
Finding the molecular formula… ☼ A 5-step process
Ex) 2.10181 x 1023 molecules of a compound is composed of 16.66g of carbon and 3.49g of hydrogen. Find
the molecular formula.
Step 1: Find the empirical formula (this is a 4-step process… see notes from last class)
Hint: pg. 93!
Step 2: Calculate the empirical molar mass.
Step 3: Calculate the molecular molar mass (if not given).
Step 4: Find the multiple.
Use: N =
molecular molar mass
empirical molar mass
Where N = the multiple
Step 5: Use the multiple to find the molecular formula.
molecular formula = N × (empirical formula)
Now: Try #47-55 on page 95.
Next Class: Checkpoint #2 – Concepts 1, 2, 3, 4, 5, 6