1. Empirical and Molecular Formulas

2. Evaluation/Assessment:
Objective:
Today I will be able to:
Calculate an empirical formula from experimental data
Derive a molecular formula from experimental data
Evaluation/Assessment:
Informal Assessment – Monitoring student interactions and questions as they complete the practice problems
Formal Assessment – Analyzing student responses to the lab and the empirical/molecular formula practice
Common Core Connection
Make sense of problem and persevere in solving them
Look for and express regularity in repeated reasoning

3. Lesson Sequence Evaluate: Warm – Up
Explain: Empirical and Molecular Formula Notes
Elaborate: Empirical and Molecular Formula Practice
Evaluate: Exit Ticket

4. Warm - Up
What is the difference between the following pairs of formulas:
CO2; C2O4
CH2O; C6H12O6

5. Objective Today I will be able to:
Calculate an empirical formula from experimental data
Derive a molecular formula from experimental data

6. Homework Work on Mole Project Due March 11
Empirical/ Molecular Formula Practice
Wear Closed Toe Shoes for Empirical and Molecular Formula Lab Monday

7. Agenda Warm-Up Empirical and Molecular Formula Notes
Empircal and Molecular Formula Practice
Exit Ticket

8. Empirical and Molecular Formula Notes

9. Empirical Formula

10. Empirical Formula
A formula that gives the simplest whole number ratio of atoms in a compound
Example: The empirical formula for hydrogen peroxide is HO (the actual formula is H2O2). This is not the actual formula; it tells you the ratio of hydrogen to oxygen is 1:1

11. Empirical Formula
A compound was analyzed and found to contain 13.5 g of Ca, 10.8 g of O, and .675 g of H. What is the empirical formula?

12. Empirical Formula Step 1: Find the mole amounts of each element
13.5 g Ca 1
1 mol
40 g Ca =
.337 mol Ca x
10.8 g O 1
1 mol
16 g O x =
.675 mol O
1 mol
1 g H
.675 g H 1
.675 mol H x =

13. Empirical Formula
Step 2: Divide each mole value by the smallest number of moles
13.5 g Ca 1
1 mol
40 g Ca =
.337 mol Ca
.337 mol x = 1
10.8 g O 1
1 mol
16 g O x =
.675 mol O
.337 mol = 2
1 mol
1 g H
.675 g H 1
.675 mol H
.337 mol = 2 x =

14. Empirical Formula Step 3: Determine the Empirical Formula Ca1O2H2 or…

15. Empirical Formula CaCl2
Determine the empirical formula for a compound containing g of Ca and g of Cl
1.203 g Ca 1
1 mol
40 g Ca
mol Ca =
________ x = 1
mol
CaCl2
2.128 g Cl 1
1 mol
35.4 g Cl =
mol Cl x
_________ = 2
mol

16. Empirical Formula Practice
Complete the practice at your desk. Ask Mr. Klotz for help if you have questions!

17. Molecular Formula

18. Molecular Formula
Is always a whole number multiple of the empirical formula
Ex: A g sample of TNT is composed of g carbon, 2.60 g hydrogen, 18.5 g nitrogen, and 42.3 g oxygen. (Its molar mass is 227 g/mol)

19. Molecular Formula C2H2NO2 Step 1: Determine the empirical formula
12 g C
2.64 mol C
31.7 g C 1
_________ 2 = = x
1.32 mol
2.60 g H 1
1 mol
1 g H
2.60 mol H x
_________ = = 2
1.32 mol
C2H2NO2
18.5 g N 1
1 mol
14 g N
1.32 mol N x =
_________ = 1
1.32 mol
42.3 g O 1
1 mol
16 g O
2.64 mol O =
________ x = 2
1.32 mol

20. Molecular Formula Step 2: Determine the empirical formula molar mass
C2H2NO2 = 72 g/mol

21. Molecular Formula 227 g/mol 72 g/mol = 3.15 or 3
Step 3: Divide the molar mass by the empirical formula molar mass
227 g/mol
72 g/mol
= or 3

22. Molecular Formula
Step 4: Multiply the empirical formula by the ratio of the molar mass to the empirical formula
3 (C2H2NO2) = C6H6N3O6

23. Molecular Formula Practice
Complete the Practice at your desk ask Mr. Klotz for help if you have questions.

24. Exit Ticket
On a scale of 1 to 5, how comfortable are you with empirical and molecular formula calculations?