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
Have your homework out on your desk for Ms. Ose to collect

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

6. Homework Mole Project Due Tuesday, March 24
Empirical/ Molecular Formula Practice
Wear Closed Toe Shoes for Empirical and Molecular Formula Lab Monday
Stoichiometry Exam Wednesday, March 25

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: Hydrogen Peroxide
Formula: H2O2
Empirical Formula: HO
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 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. Molecular Formula

17. Molecular Formula
Is always a whole number multiple of the empirical formula
Ex: A g sample of TNT is composed of 31.7 g carbon, 2.60 g hydrogen, 18.5 g nitrogen, and 42.3 g oxygen. (Its molar mass is 227 g/mol)

18. 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

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

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

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

22. Empirical and Molecular Formula Practice
Complete the Practice at your desk ask Ms. Ose for help if you have questions.

23. Exit Ticket
Determine if the formulas listed below are Empirical or Molecular Formulas CO2 C6H12O6 P2O5 N2H6 CaCl2 Joke of the day: What do you get when you mix sulfur, tungsten and silver?

24. Answer
SWAg