1. Empirical Formulas

2. Reading activity With a partner take turns reading pages 241-246
Discuss the relationships between the following words and create a small word web to show how they are related
Molecular Formula
Empirical Formula
Percent Composition
Mole
Molar Mass
“n”

3. Definition
Empirical Formulas of a chemical compound is shows the smallest whole number ratio of elements in a compound.
Standard for ionic compounds

4. Where does it come from?
The term empirical refers to a process of elemental analysis used to determine relative percent composition of a pure chemical substance by element.

5. Molecular Formula
Molecular Formula identifies the absolute number of atoms of such elements to be found in each discrete molecule of that compound.

6. Examples Compound Empirical Molecular Multiplier Water H2O 1
Hydrogen peroxide HO
H2O2 2
Propylene
CH2
C3H6 3
Glucose
CH2O
C6H12O6 6
Vitamin C
C3H4O3
C6H8O6

7. You may be given the following info:
The masses of the elements in a weighed sample of the compound
The mass percents of the element in the compound
Assume a 100-g sample and calculate the masses of each element in that sample

8. From the information given…
Find the number of moles of each element. (Gram to mole conversion usually)
Find the simplest mole ratio and set that to 1.
Find all other mole ratios.
Apply the mole ratios as subscripts for your simple formula.
If a mole ratio is X 0.5, then multiply ALL mole ratios by 2.

9. #1 0.6884gPb = 3.322*10-3 0.2356gCl = 6.6646*10-3 Mass of Pb
Mass of Cl

10. Divide by the smallest number
Pb = mol Pb
Cl: = mol Cl
ANSWER: PbCl2
Divide by the smallest number

11. #2
HINT: Assume 100 grams
Answer: C6NH11O
Answer #3: C3H3O

12. Molecular Formulas 71.65 g Cl = 2.021mol Cl 24.27 g C = 2.021mol C
4.07 g H = 4.04mol H
Ratio: ClCH2

13. The molar mass of ClCH2 is 49.48 g (empirical formula mass)
= = 2 ;
thus the Molecular Formula is (ClCH2)2 or Cl2C2H4

14. Practice Problems Complete on the back or new page in your notebook