Empirical and Molecular Formulas

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

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

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

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

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

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

Empirical and Molecular Formula Notes

Empirical Formula

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

Empirical Formula A compound was analyzed and found to contain 13.5 g of Ca, 10.8 g of O, and 0.675 g of H. What is the empirical formula?

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 =

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 =

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

Empirical Formula CaCl2 Determine the empirical formula for a compound containing 1.203 g of Ca and 2.128 g of Cl 1.203 g Ca 1 1 mol 40 g Ca .03008 mol Ca = ________ x = 1 .03008 mol CaCl2 2.128 g Cl 1 1 mol 35.4 g Cl = .06011 mol Cl x _________ = 2 .03008 mol

Molecular Formula

Molecular Formula Is always a whole number multiple of the empirical formula Ex: A 100.0 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)

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

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

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

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

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

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?

Answer SWAg