1. Empirical Formula

2. No, you can reduce it to HO
Empirical Formula:
Lowest whole # ratio
H2O2 (hydrogen peroxide) is it an empirical Formula?
No, you can reduce it to HO

3. H2O2 is the molecular formula
Molecular formula shows the way the molecule is actually found in nature.

4. How do we write empirical formulas???
1. Take the % compositions and convert the % to grams.

5. 11.1 % H % O
changes to
11.1 g H g O

6. Take the % compositions and convert the % to grams.
Convert grams to moles

7. 11.1 g H x 1 mole H = 11.1 moles
1.0 g H
88.9 g O x 1 mole O = 5.5 moles
16.0 g O

8. Take the % compositions and convert the % to grams.
Convert grams to moles
Divide by the smallest # of moles

9. 11.1 moles H / 5.5= 2
5.5 moles O / 5.5 =1

10. Take the % compositions and convert the % to grams.
Convert grams to moles
Divide by the smallest # of moles

11. Plug the whole #’s into the empirical formula

12. 11.1 moles H / 5.5= 2
5.5 moles O / 5.5 =1
H2O1

13. Take the % compositions and convert the % to grams.
Convert grams to moles
Divide by the smallest # of moles
Plug the whole #’s into the empirical formula
If you do not have whole #’s after dividing you must multiply through to make them all whole #’s

14. Examples
1.5 x 2 = 3
1.3 x 3 = 4
1.25 x 4 = 5
1.75 x 4 = 7

15. Examples
Mn1O1.5
2x (Mn1O1.5)=
Mn2O3

16. Molecular Mass
Vs.
Empirical Mass

17. Is found experimentally
Molecular Mass
Is found experimentally

18. Is found using the molar mass from the periodic table.
Empirical Mass
Is found using the molar mass from the periodic table.

19. Molecular Mass
Vs.
Empirical Mass
If they are the same GREAT the Molecular Formula and Empirical Formula are the same

20. Molecular Mass
Vs.
Empirical Mass
If they are not the same you must divide the Molecular mass by the Empirical mass to see how many time greater it is.

21. Molecular mass = 78g/mol Empirical mass of CH =13g/mol Molecular Mass
Vs.
Empirical Mass
Molecular mass = 78g/mol
Empirical mass
of CH =13g/mol
78/13 =6

22. Molecular Mass
Vs.
Empirical Mass
Since the molecular mass is 6 times greater then the empirical mass the formula is also 6 times greater.

23. Molecular Mass
Vs.
Empirical Mass
6 x (CH)
C6H6
Molecular Formula

24. Using the formula you have just found you can calculate % composition.

25. You find the % just like you would for any %
% Composition
You find the % just like you would for any %
Individual atom mass
Total mass of the compound
X100%

26. Example: Water H2O = total mass 18.0 Mass from H= 2(1.0)=2.0
% Composition
Example: Water
H2O = total mass 18.0
Mass from H= 2(1.0)=2.0
% comp. = 2/18x100%
% comp. = 11% H in H2O