Empirical and Molecular Formulas

Objective: Objective: – Today I will be able to: Determine the limiting reactant of a chemical reaction by completing a lab Determine the limiting reactant of a chemical reaction by completing a lab Calculate an empirical formula from experimental data Calculate an empirical formula from experimental data Derive a molecular formula from experimental data Derive a molecular formula from experimental data Evaluation/Assessment: Evaluation/Assessment: – Informal Assessment – Monitoring student interactions as they complete the practice and the lab – Formal Assessment – Analyzing student responses to the lab and the empirical/molecular formula practice Common Core Connection Common Core Connection – Make sense of problem and persevere in solving them – Look for and express regularity in repeated reasoning – Attend to precision – Use appropriate tools strategically

Lesson Sequence Evaluate: Warm – Up Evaluate: Warm – Up Evaluate: Review Limiting Reactants Evaluate: Review Limiting Reactants Engage and Explore: Silver Nitrate Lab Engage and Explore: Silver Nitrate Lab Explain: Empirical and Molecular Formula Notes Explain: Empirical and Molecular Formula Notes Elaborate: Empirical and Molecular Formula Practice Elaborate: Empirical and Molecular Formula Practice Evaluate: Exit Ticket Evaluate: Exit Ticket

Warm - Up Given 50 grams of H 2 and O 2, what is the limiting reactant in the reaction? Given 50 grams of H 2 and O 2, what is the limiting reactant in the reaction? – H 2 + O 2  2H 2 O

Objective Today I will be able to: Today I will be able to: Determine the limiting reactant of a chemical reaction by completing a lab Determine the limiting reactant of a chemical reaction by completing a lab Calculate an empirical formula from experimental data Calculate an empirical formula from experimental data Derive a molecular formula from experimental data Derive a molecular formula from experimental data

Homework Work on Mole Project Due March 7 Work on Mole Project Due March 7 – Sewing help session after school February 27 Empirical/ Molecular Formula Practice Empirical/ Molecular Formula Practice

Agenda Warm-Up Warm-Up Review Limiting Reactants Review Limiting Reactants Day 1: Silver Nitrate Lab Day 1: Silver Nitrate Lab Empirical and Molecular Formula Notes Empirical and Molecular Formula Notes Empircal and Molecular Formula Practice Empircal and Molecular Formula Practice Exit Ticket Exit Ticket

Limiting Reactants What questions do you have about the Limiting Reactant Practice?

Silver Nitrate Lab Day 1

Silver Nitrate Lab Safety Wear goggles, aprons and closed toe shoes in the lab Wear goggles, aprons and closed toe shoes in the lab Do not spill silver nitrate on your hand. It will stain your hands. Do not spill silver nitrate on your hand. It will stain your hands. Today we are setting up the reaction. Next class you will get results and perform the calculation Today we are setting up the reaction. Next class you will get results and perform the calculation

Empirical and Molecular Formula Notes

Empirical Formula

A formula that gives the simplest whole number ratio of atoms in a compound 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 H 2 O 2 ). This is not the actual formula; it tells you the ratio of hydrogen to oxygen is 1:1 Example: The empirical formula for hydrogen peroxide is HO (the actual formula is H 2 O 2 ). 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.675 g of H. What is the 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?

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

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

Empirical Formula Step 3: Determine the Empirical Formula Step 3: Determine the Empirical Formula Ca 1 O 2 H 2 or… Ca 1 O 2 H 2 or… Ca(OH) 2 Ca(OH) 2

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

Empirical Formula Practice Complete the practice at your desk. Ask Ms. Ose for help if you have questions!

Molecular Formula

Is always a whole number multiple of the empirical 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) 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)

Molecular Formula Step 1: Determine the empirical formula Step 1: Determine the empirical formula 31.7 g C g H 1 1 mol 12 g C 1 mol 1 g H x x = = 2.64 mol C 2.60 mol H ________ _________ 1.32 mol = = 1 2 C 2 H 2 NO g N g O 1 x x 1 mol 14 g N 1 mol 16 g O = = _________ 1.32 mol N 2.64 mol O 1.32 mol = = 2 2

Molecular Formula Step 2: Determine the empirical formula molar mass Step 2: Determine the empirical formula molar mass C 2 H 2 NO 2 = 72 g/mol C 2 H 2 NO 2 = 72 g/mol

Molecular Formula Step 3: Divide the molar mass by the empirical formula molar mass 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 Step 4: Multiply the empirical formula by the ratio of the molar mass to the empirical formula 3 (C 2 H 2 NO 2 ) = C 6 H 6 N 3 O 6 3 (C 2 H 2 NO 2 ) = C 6 H 6 N 3 O 6

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

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