empirical and molecular formulas. objective: objective: – today i will be able to: determine the...

Empirical and Molecular Empirical and Molecular FormulasFormulas

• Objective:Objective:– Today I will be able to:Today I will be able to:

• Determine the limiting reactant of a chemical reaction by Determine the limiting reactant of a chemical reaction by completing a labcompleting a lab

• Calculate an empirical formula from experimental dataCalculate an empirical formula from experimental data• Derive a molecular formula from experimental dataDerive a molecular formula from experimental data

• Evaluation/Assessment:Evaluation/Assessment:– Informal Assessment – Monitoring student Informal Assessment – Monitoring student

interactions as they complete the practice and the interactions as they complete the practice and the lablab

– Formal Assessment – Analyzing student responses to Formal Assessment – Analyzing student responses to the lab and the empirical/molecular formula practicethe lab and the empirical/molecular formula practice

• Common Core ConnectionCommon Core Connection– Make sense of problem and persevere in solving Make sense of problem and persevere in solving

them them – Look for and express regularity in repeated reasoning Look for and express regularity in repeated reasoning – Attend to precision Attend to precision – Use appropriate tools strategically Use appropriate tools strategically

Lesson SequenceLesson Sequence

• Evaluate: Warm – UpEvaluate: Warm – Up

• Evaluate: Review Limiting ReactantsEvaluate: Review Limiting Reactants

• Engage and Explore: Silver Nitrate LabEngage and Explore: Silver Nitrate Lab

• Explain: Empirical and Molecular Formula Explain: Empirical and Molecular Formula NotesNotes

• Elaborate: Empirical and Molecular Elaborate: Empirical and Molecular Formula PracticeFormula Practice

• Evaluate: Exit TicketEvaluate: Exit Ticket

Warm - UpWarm - Up

• Given 50 grams of HGiven 50 grams of H22 and O and O22, what is , what is the limiting reactant in the reaction?the limiting reactant in the reaction?– HH2 2 + O+ O2 2 2H 2H22OO

ObjectiveObjective

• Today I will be able to:Today I will be able to:•Determine the limiting reactant of a Determine the limiting reactant of a

chemical reaction by completing a labchemical reaction by completing a lab

•Calculate an empirical formula from Calculate an empirical formula from experimental dataexperimental data

•Derive a molecular formula from Derive a molecular formula from experimental dataexperimental data

HomeworkHomework

• Work on Mole Project Due March 7Work on Mole Project Due March 7– Sewing help session after school Sewing help session after school

February 27February 27

• Empirical/ Molecular Formula PracticeEmpirical/ Molecular Formula Practice

AgendaAgenda

• Warm-UpWarm-Up

• Review Limiting ReactantsReview Limiting Reactants

• Day 1: Silver Nitrate LabDay 1: Silver Nitrate Lab

• Empirical and Molecular Formula NotesEmpirical and Molecular Formula Notes

• Empircal and Molecular Formula Empircal and Molecular Formula PracticePractice

• Exit TicketExit Ticket

Limiting ReactantsLimiting Reactants

What questions do you have What questions do you have about the Limiting Reactant about the Limiting Reactant

Practice?Practice?

Silver Nitrate Lab Day 1Silver Nitrate Lab Day 1

Silver Nitrate Lab SafetySilver Nitrate Lab Safety

• Wear goggles, aprons and closed toe Wear goggles, aprons and closed toe shoes in the labshoes in the lab

• Do not spill silver nitrate on your Do not spill silver nitrate on your hand. It will stain your hands.hand. It will stain your hands.

• Today we are setting up the reaction. Today we are setting up the reaction. Next class you will get results and Next class you will get results and perform the calculationperform the calculation

Empirical and Molecular Empirical and Molecular Formula NotesFormula Notes

Empirical FormulaEmpirical Formula

Empirical FormulaEmpirical Formula

• A formula that gives the simplest whole A formula that gives the simplest whole number ratio of atoms in a compoundnumber ratio of atoms in a compound

• Example: The empirical formula for Example: The empirical formula for hydrogen peroxide is HO (the actual hydrogen peroxide is HO (the actual formula is Hformula is H22OO22). This is not the actual ). This is not the actual formula; it tells you the ratio of formula; it tells you the ratio of hydrogen to oxygen is 1:1hydrogen to oxygen is 1:1

Empirical FormulaEmpirical Formula

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

Empirical FormulaEmpirical Formula

• Step 1: Find the mole amounts of Step 1: Find the mole amounts of each elementeach element

13.5 g Ca

1

1 mol40 g Ca

10.8 g O

1

1 mol16 g

O

.675 g H1

1 mol1 g H

x

x

x =

=

= .337 mol Ca

.675 mol O

.675 mol H

Empirical FormulaEmpirical Formula

• Step 2: Divide each mole value by Step 2: Divide each mole value by the smallest number of molesthe smallest number of moles

13.5 g Ca

1

1 mol40 g Ca

10.8 g O

1

1 mol16 g

O

.675 g H1

1 mol1 g H

x

x

x =

=

= .337 mol Ca

.337 mol.675 mol O.337 mol

.675 mol H.337 mol

=

=

=

1

2

2

Empirical FormulaEmpirical Formula

• Step 3: Determine the Empirical Step 3: Determine the Empirical FormulaFormula

• CaCa11OO22HH2 2 or…or…

• Ca(OH)Ca(OH)22

Empirical FormulaEmpirical Formula

• Determine the empirical formula for Determine the empirical formula for a compound containing 1.203 g of Ca a compound containing 1.203 g of Ca and 2.128 g of Cland 2.128 g of Cl

1.203 g Ca

12.128 g

Cl1

1 mol40 g Ca

1 mol35.4 g

Cl

x

x =

=

.03008 mol Ca

.06011 mol Cl

________

_________

.03008 mol

.03008 mol

=

=

1

2

CaCl2

Empirical Formula PracticeEmpirical Formula Practice

Complete the practice at your Complete the practice at your desk. Ask Ms. Ose for help if desk. Ask Ms. Ose for help if

you have questions!you have questions!

Molecular FormulaMolecular Formula

Molecular FormulaMolecular Formula

• Is always a whole number multiple of Is always a whole number multiple of the empirical formulathe empirical formula

• Ex: A 100.0 g sample of TNT is Ex: A 100.0 g sample of TNT is composed of 31.7 g carbon, 2.60 g composed of 31.7 g carbon, 2.60 g hydrogen, 18.5 g nitrogen, and 42.3 hydrogen, 18.5 g nitrogen, and 42.3 g oxygen. (Its molar mass is 227 g oxygen. (Its molar mass is 227 g/mol)g/mol)

Molecular FormulaMolecular Formula

• Step 1: Determine the empirical formulaStep 1: Determine the empirical formula

31.7 g C

1

2.60 g H1

1 mol12 g C

1 mol1 g H

x

x =

=

2.64 mol C

2.60 mol H

________

_________

1.32 mol

1.32 mol

=

=

1

2

C2H2NO218.5 g N1

42.3 g O1

x

x

1 mol14 g

N1 mol16 g O

=

=

_________

_________

1.32 mol N

2.64 mol O

1.32 mol

1.32 mol

=

=

2

2

Molecular FormulaMolecular Formula

• Step 2: Determine the empirical Step 2: Determine the empirical formula molar massformula molar mass

• CC22HH22NONO2 2 = 72 g/mol= 72 g/mol

Molecular FormulaMolecular Formula

• Step 3: Divide the molar mass by the Step 3: Divide the molar mass by the empirical formula molar massempirical formula molar mass

227 g/mol

72 g/mol= 3.15 or 3

Molecular FormulaMolecular Formula

• Step 4: Multiply the empirical formula Step 4: Multiply the empirical formula by the ratio of the molar mass to the by the ratio of the molar mass to the empirical formulaempirical formula

• 3 (C3 (C22HH22NONO22) = C) = C66HH66NN33OO66

Molecular Formula PracticeMolecular Formula Practice

Complete the Practice at your Complete the Practice at your desk ask Ms. Ose for help if desk ask Ms. Ose for help if

you have questions.you have questions.

Exit TicketExit Ticket

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