Stoichiometry

1
Stoichiometry

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• Mr. Chan
• Northwestern University

2
Determining Avogadros Number

• Website

3
Lab Quantitative Analysis

• Objectives
• Measure number of moles of iron consumed and
  copper produced in a reaction
• Determine the coefficients of the balanced
  chemical reaction
• Hypothesis
• Write the balanced equation for the reaction of
  iron metal and copper(II)chloride
• Identify the type of reaction
• Predict observations for the reaction
• Techniques
• Decanting
• Using balances
• Peer Review of Labs 23 (AW 79) during waiting
  time

4
Exit Slips July 1, 2004

• 1) What amount of experience have you had with
  Chemistry?
• 2a) For those who have not taken 1 full year of
  Chem before, how do you feel thus far? Which
  parts are overwhelming? (HW, LAB, QUIZZES, Pace)
  What suggestions do you have to help improve
  your experience?
• 2b) For those who have taken at least 1 year of
  Chem, how do you feel thus far? Is the class
  supporting and enhancing your knowledge? Is
  there too much repetition with your previous
  class? What are your motivations for taking this
  class? (AP?, SAT II?) What suggestions do you
  have to help improve your experience?
• 3) Identify at least one area that you feel
  confident in for tomorrows exam.
• 4) Identify at least one area that you will need
  to review for tomorrows exam.

5
Today (Day 99)

• (0-20) Return/Discuss Tests, formula buddy
• (20-30) Stoichiometry in Real Life
• (30-40) Interpreting Chemical Equations
• (40-43) Review/Summary Cornell Notes, Flaming
  Cheeto
• (0-10) Project Debrief
• (10-30) Present Animations, Videos
• (30-43) HW Head Start, Grades updates

6
Calculations with Nonchemical Reactions

• Recipes Cooking, Baking
• Grams to Moles Masses of foods to amounts
  (cups, tsp, tbsp)
• Limiting Reactants
• Excess Reactants
• Percent Yield

7
Interpreting Chemical Equations

• 1) Particles (molecules and atoms) coefficients
  particle ratios
• 2) Moles (1 mole 6.02 x 1023 particles)
  coefficients mole ratios
• 3) Mass conserved in equation, coefficients
  are mole ratios, not mass ratios
• 4) Volumes use molar volume (at STP)
  coefficients Liter ratios
• 5) Only mass and number of atoms are conserved
  in every reaction
• Practice 3-4
• Example Interpret a) number of representative
  particles, b) number of moles, c) volumes of
  gases at STP
• I) H2(g) O2(g) yields H2O(g)
• 2) C2H2(g) O2(g) yields CO2(g) H2O(l)

8
Today (Day 100)

• (0-10) Discuss HW
• (10-20) Warmup/Review
• H2S O2 yields SO2 H2O
• Balance chemical equation, Interpret
• What if
• 1.5 moles O2
• 6 moles O2
• 5 moles O2
• (20-35) Mole-Mole Calculations
• (35-43) Summary, HW Head Start

9
Mole-Mole Calculations

• Molar ratios, Dimensional Analysis
• Can determine amount of product, amount of
  reactant with another reactant, amount of product
  from amount of reactant
• Easy calculations (do in head, think)
• Harder use ratios
• Starting quantity times ratio what goes on
  top? bottom?
• Practice
• Al O2 yields Al2O3
• 14.8 mol Al how much O2 reacts?
• 3.7 mol Al2O3 from how much Al?
• 0.78 mol O2 how much Al2O3 formed

10
Today (Day 101)

• (0-10) Discuss HW
• (10-25) Mass Mass calculations
• (25-30) PreLab
• (30-43, 0-43) Lab Empirical Formulas
• Discuss PostLab
• Warmup/Review (5-15)
• N2 3H2 yields 2NH3
• Calculate moles of nitrogen and hydrogen to make
  7.24 mol of ammonia

11
Mass to Mass calculations

• Cannot measure moles in lab,
• Must convert from moles toMASS (grams)
• Setup road map (Grams, Moles, Moles, Grams) Other
  calculations
• Mole to mole
• Mole to mass, mass to mole
• Example
• CaC2 2H2O yields C2H2 Ca(OH)2
• 49.0 g H2O how many moles of CaC2 will combine?
• 5.00 g of CaC2 how many grams of C2H2 produced?
• Practice 9-12

12
Today (Day 102)

• (0-10) Warmup/Review
• 2C2H2 5O2 yields 4CO2 2H2O
• 52.0g of C2H2 burns how many grams CO2 and H2O
  produced?
• 52.0 g of C2H2 burns with how many grams of
  oxygen?
• (10-15) Discuss HW
• (15-30) Other Stoichiometric Calcs
• (30-43) Post Lab w/ peer groups
• Prelab Start Lab (0-20min)
• PostLab Empirical Formulas (20-30)
• Jigsaw Problem Set (0-15)
• Finish Lab (15-43)

13
Other Calculations

• Mass to mole to particles (atoms, molecules,
  formula units)
• Example
• 2H2O yields 2H2 O2
• 29.2 grams of water produces how many molecules
  of oxygen?
• Volumes using 22.4 L/mol at STP
• Examples
• 2C2H2 5O2 yields 4CO2 2H2O
• With _______moles of C2H2, how many Liters of CO2
  formed at STP?
• Practice 13-18

14
Today (Day 103)

• (0-10) Questions before Quiz
• (10-35) Quiz (through 8.4) (10-30)

15
Today (Day 104)

• (0-10) Warmup/Review
• CaCO3 yields CaO CO2
• 24.8 grams of CaCO3 heated to form how many grams
  of CaO?
• (10-30) Discuss Quiz
• HONORS Limiting Reactant (0-15)
• (30-43) Prelab (15-20)
• (0-43) Lab (20-43)

16
Identifying the Limiting Reactant

• Recipes review limiting reactant
• Chemistry LR
• Reactant that is in short supply
• Determines the amount of product that can be
  formed in a reaction
• Excess reagent
• Not completely used up
• Determine with LR how much gets used and what is
  left over
• Examples
• Must determine how much of reactant goes with
  other reactant
• Have/Will use
• 2Na Cl2 yields 2NaCl
• 6.70 mol Na with 3.20 mol
• Practice
• Must determine which is LR first!

17
Today (Day 105)

• (0-43) Video
• (0-43) Problem Set group work

18
Today (Day 106)

• (0-20) Lab Day 2
• (20-43) Problem Set group work
• (0-43) Smores Lab
• Warmup/Review (15-25)
• CaC2 2H2O yields C2H2 Ca(OH)2
• 1.50 grams of CaC2 how many moles of C2H2 will
  be formed?

19
Calculating Theoretical and Percent Yield

• Theoretical yield
• Calculated from reaction (stoichiometry)
• Represents maximum amount formed from reactants
• Actual yield
• Determined from experiment
• Given in a problem, or done in the lab
• Percent Yield
• Ratio of actual to theoretical
• Actual/theoretical x 100
• Should not be 100 - what are some reasons why
• Usually
• Examples
• Lab Moles and Mass in Reaction
• CaCO3 yields CaO CO2
• If theo yield is 13.9 grams, and actual yield is
  13.1 grams, what is percent yield?
• 2Al 3CuSO4 yields Al2(SO4)3 3Cu
• If 1.87 grams of Al reacts, how much copper is
  produced?
• Calc percent yield if 4.65 of copper is actually
  produced.

20
Today (Day 107)

• Warmup/Review (0-10)
• Cooking Recipe practice with Limiting Reactants
• Lab Day 3
• Chapter 8 Review

21
Today (Day 108)

• Chapter 8 Test

22
Today (Day 65)

• Warmup/Review (0-15)
• Theo yield and Percent Yield
• Sb2S3 3Fe yields 2Sb 3FeS
• When 15.0 g of Sb2S3 reacts, 9.84 g Sb is
  produced. What is the percent yield of this
  reaction?
• Discuss HW (15-30)
• Review Questions, concepts (30-43)
• Syllabus Check (0-15)
• Smore Stoichiometry (15-43)

23
Lab Chemical Reactions

• Objectives
• Carry out several chemical reactions
• Write balanced chemical equations
• Observe Law of Definite Composition and
  Conservation of Mass in experiment
• Convert Copper metal into several forms of Copper
  compounds
• Techniques
• Measuring volume
• Working with strong acids and bases
• Decanting, using litmus paper
• Include Title, Observations and Equations, and
  Quantitative Analysis in notebook no formal
  write-up

24
Entrance Slips (for Monday)

• Upon entering class on Monday, please write one
  paragraph on the following
• How I saw, used, or learned something about
  Chemistry this weekend.
• Happy 4th of July!
• See you at Evanstons fireworks!