Do Now for 3 22 10 1 If you have

“Do Now” for 3/22/10 1. If you have a dozen of something, how many do you have? 12 2. How many is in a pair? 3. Can you think of any 2 other terms used to describe a specific # of something? Ream = 500 Gross = 144 Baker’s dozen = 13 Take out your HW!

1 Mole = 6. 02 x 10 23

Quick Announcements • You will have several smaller HW assignments this week – don’t forget about them and end up falling behind! • 2 pts extra credit (or not penalized forgetting your book) added daily to your “Do Now” pts. for bringing your calculators to class every day this week!

Cornell Notes: Ch. 10 – The Mole • Atoms are really, small, so how can scientists possibly make any measurements on them? – To have a visible quantity of a substance, there must therefore be a very large # of atoms, molecules, or particles. – Moles are the standard unit of measurement for measuring atoms, molecules, or particles. 1 mole = 602 200 000 000 000 1 mole = 6. 02 x 1023 • Moles. Yes - using scientific notation! are. Is there an easier way to write like a scientist’s dozen this gigantic #? – a conveniently sized bundle for working with the kind of stuff chemists work with: atoms & molecules

Weighing out a single atom is nearly impossible. Weighing out 6. 02 x 1023 atoms, though, is do-able. • 6. 02 x 1023 atoms of carbon weigh 12. 01 grams carbon 12. 01 grams • 6. 02 x 1023 atoms of copper weigh 63. 55 grams copper • 6. 02 x 1023 atoms of helium weigh 4. 003 grams. helium Where have you seen those #’s before? The atomic mass on the periodic table can tell you 2 different masses: 1. Mass of a single particle units are ‘a. m. u. ’ 2. Mass of a mole of that element units are in grams Pay attention to what units you are given!!

Let’s Practice! • How much does 1 mole of the following elements weigh? – Oxygen 15. 9999 g – Silver 107. 868 g – Mercury 200. 59 g • How many moles do you have of each element if you have the following masses? – 32 g of Oxygen 2 moles – 324 g of Silver 3 moles • What would be the mass of 4 Mercury atoms? 802. 36 amu

So Just How Big is a Mole? 1 mole = 602 200 000 000 000 One mole of marbles would cover the entire Earth (oceans included) for a depth of three miles. One mole of $100 bills stacked one on top of another would reach from the Sun to Pluto and back 7. 5 million times. It would take light 9500 years to travel from the bottom to the top of a stack of 1 mole of $1 bills. One mole of hockey pucks would equal the mass of the moon.

• If 1 mole of pennies was divided up equally between all the people on Earth, you would have enough money to spend a million dollars every hour, 24 hours a day, for your entire life. • When you died, you would have spent less than half of your riches. 6. 02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon. 6. 02 X 1023 Grains of Sand: Would be more than all of the sand on Miami Beach.

1 Mole of Particles

Cornell Notes: Ch. 10 – The Mole Counting Atoms: • Chemistry is a quantitative science - we need a "counting unit. " There are 6. 022 x 1023 particles in a mole of any substance. ? quadrillions trillions billions thousands millions 1 mole = 60221367360000000 or 6. 022 x 1023

Avogadro’s Number q A MOLE of any substance contains as many elementary units (atoms and molecules) as the number of atoms in 12 g of the isotope of carbon-12. q This number is called AVOGADRO’s number NA = 6. 02 x 1023 particles/mol q The mass of one mole of a substance is called MOLAR MASS symbolized by MM q Units of MM are g/mol q Examples H 2 hydrogen 2. 02 g/mol He helium 4. 0 g/mol N 2 nitrogen 28. 0 g/mol O 2 oxygen 32. 0 g/mol CO 2 carbon dioxide 44. 0 g/mol

Molecular Weight and Molar Mass Molecular weight is the sum of atomic weights Molecular weight of all atoms in the molecule. example: Na. Cl has a molecular weight of 58. 5 a. m. u. this is composed of a single molecule of Na. Cl Remember: a. m. u. means atomic mass units Molar mass = molecular weight in grams (MM). Molar mass example: Na. Cl has a molar mass of 58. 5 grams this is composed of a 6. 02 x 1023 molecules of Na. Cl

The Molar Mass and Number of Particles in One-Mole Quantities Substance Molar Mass Number of Particles in One Mole Carbon (C) 12. 0 g 6. 02 x 1023 C atoms Sodium (Na) 23. 0 g 6. 02 x 1023 Na atoms Iron (Fe) 55. 9 g 6. 02 x 1023 Fe atoms Na. F (preventative for dental cavities) 42. 0 g 6. 02 x 1023 Na. F formula units Ca. CO 3 (antacid) 100. 1 g 6. 02 x 1023 Ca. CO 3 formula units C 6 H 12 O 6 (glucose) 180. 0 g 6. 02 x 1023 glucose molecules C 8 H 10 N 4 O 2 (caffeine) 194. 0 g 6. 02 x 1023 caffeine molecules

Chemical Equations N 2 (g) 3 H 2 (g) + 2 NH 3 (g) + “Microscopic recipe” “Macroscopic recipe” 1 molecule N 2 + 1 mol N 2 + 3 molecules H 2 3 mol H 2 Experimental Conditions Reactants 2 molecules NH 3 2 mol NH 3 Products Before reaction 1 mol N 2 + 3 mol H 2 2 mol NH 3 2 molecules N 2 3 molecules H 2 0 molecules NH 3 1 molecules N 2 0 molecules H 2 2 molecules NH 3 After reaction

Exploding Flour FLOUR 6” PVC Pipe EXPLOSION: Fuel (flour) Ignition (candle) Oxygen (combustion) As confinement increases, EXPLOSION is greater.

Combustion of a Hydrocarbon GENERAL FORMULA: CH + O 2 CO 2 + H 2 O Many homes get heat from propane (C 3 H 8) heaters. Write a balanced chemical equation for the complete combustion of propane gas. C 3 H 8(g) + O 2(g) CO 2(g) + H 2 O(g) C 3 H 8(g) + 5 O 2(g) 3 CO 2(g) + 4 H 2 O(g) + energy

Combustion of Hydrocarbon (cont. ) Ideal Stoichiometry C 3 H 8(g) + 5 O 2(g) 3 CO 2(g) + 4 H 2 O(g) + energy D Too ‘rich’ (not enough oxygen – too much fuel) C 3 H 8(g) + 3 O 2(g) D CO (g) + 4 H 2 O(g) + energy C 3 H 8(g) + 2 O 2(g) 3 C (g) + 4 H 2 O(g) SOOT + energy

Air-Fuel Ratio in an Internal Combustion Engine Stoichiometric ratio Relative emissions of pollutants Fuel-rich mixtures Fuel-lean mixtures NO RH CO 12 13 14 15 Mass ratio of air to fuel Hill, Petrucci, General Chemistry An Integrated Approach 2 nd Edition, page 1087 16 17

Catalytic converter Before it reaches the catalytic converter, the exhaust contains such pollutants as NO, CO, and hydrocarbons. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. Tail pipe After it has passed through the catalytic converter, the exhaust contains water vapors, N 2, O 2, and CO 2.

Combustion of Methane Gas Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 245

Combustion of Methane Gas One methane molecule CH 4 1 carbon + 4 hydrogen Two oxygen molecules + One carbon dioxide molecule Two water molecules 2 O 2 CO 2 2 H 2 O 4 oxygen Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 245 = 1 carbon + 2 oxygen + 4 hydrogen

Combustion of Glucose Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 130

Combustion of Iron • Formation of Rust 4 Fe + O 2 2 Fe 2 O 3 • Thermite Reaction • underwater welding • Temp. = ~3500 o. C Fe 2 O 3 + 2 Al 2 Fe + Al 2 O 3 + 199 kcal

Combustion of Copper • Copper burns with a green color • Copper forms a patina (oxide) – green in color • Cu. O 2 – black in color Statue of Liberty is covered with copper that has oxidized to form copper (II) oxide, Cu. O 2. • Cu. O

Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Na Cl 2 Cl Cl 2 Na. Cl Na General form: A + B AB element or compound

Synthesis Reaction Direct combination reaction (Synthesis) 2 Mg + Mg 2+ Mg O 2 2 Mg. O O 2 O Mg 2+ Mg General form: A + B AB element or compound

Decomposition Reaction Decomposition reaction 2 H 2 O 2 H 2 + O 2 H O H + H O H General form: AB compound A + B two or more elements or compounds

Formation of a solid Ag. Cl Ag. NO 3(aq) + KCl(aq) KNO 3 (aq) + Ag. Cl(s)

Single and Double Replacement Reactions Single-replacement reaction Mg + Cu. SO 4 Mg. SO 4 + Cu General form: A + BC AC + B Double-replacement reaction Ca. CO 3 + 2 HCl Ca. Cl 2 + H 2 CO 3 General form: AB + CD AD + CB

Activity Series Element Reactivity Foiled again – Aluminum loses to Copper Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H 2 Cu Hg Ag Pt Au Halogen Reactivity F 2 Cl 2 Br 2 I 2

Potassium reacts with Water POW!

Single and Double Replacement Reactions Single-replacement reaction Mg + Cu. SO 4 Mg. SO 4 + Cu General form: A + BC AC + B Double-replacement reaction Ca. CO 3 + 2 HCl Ca. Cl 2 + H 2 CO 3 General form: AB + CD AD + CB

Single and Double Replacement Reactions Single-replacement reaction Mg + Cu. SO 4 Mg. SO 4 + Cu General form: A + BC AC + B Double-replacement reaction Ca. CO 3 + 2 HCl Ca. Cl 2 + H 2 CO 3 General form: AB + CD AD + CB

Double Replacement Reaction

How Big is a Mole? One mole of marbles would cover the entire Earth (oceans included) for a depth of two miles. One mole of $1 bills stacked one on top of another would reach from the Sun to Pluto and back 7. 5 million times. It would take light 9500 years to travel from the bottom to the top of a stack of 1 mole of $1 bills.

Amedeo Avogadro ? quadrillions trillions billions thousands millions 1 mole = 60221367360000000 or 6. 022 x 1023

Welcome to Mole Island 1 mol = molar mass 1 mole = 22. 4 L @ STP 1 mol = 6. 02 x 1023 particles

Stoichiometry Island Diagram Known Unknown Substance A Substance B M Mass Mountain Mass Mole Island Liter Lagoon V Volume Mole Volume Particles P Particle Place Stoichiometry Island Diagram

Stoichiometry Island Diagram Known Mass Substance A 1 Substance B ) (g ss m ole = Mass a rm m ola r a ol m as s( Volume Unknown g) Use coefficients from balanced chemical equation 1 mole = 22. 4 L @ STP Mole e ol m = m 1 1 mole = 22. 4 L @ STP Mole Volume (gases) les Particles 1 c rti pa ) 23 0 les x 1 lecu 2 o 02 6. or m = s m ole (ato m Stoichiometry Island Diagram 1 m ole (a to m = 6. 02 so 2 x 1 0 23 ole pa cu r les ticle s ) rm Particles

Stoichiometry Island Diagram Known Unknown Substance A Substance B M Mass Mountain Mass Liter Lagoon V Volume Mole Volume Particles P Particle Place Stoichiometry Island Diagram

Visualizing a Chemical Reaction 2 2 Na + Cl 2 Na. Cl 10 ___ mole Na 5 ___ mole Cl 2 10 ? ___ mole Na. Cl

Visualizing a Chemical Reaction 2 2 Na + Cl 2 Na. Cl 10 ___ mole Na 5 ___ mole Cl 2 10 ___ mole Na. Cl

Formation of Ammonia N 2 (g) 3 H 2 (g) + 2 NH 3 (g) + 2 atoms N + 6 atoms H 2 atoms N and 6 atoms H 1 molecule N 2 + 3 molecules H 2 2 molecules NH 3 10 molecule N 2 + 30 molecules H 2 20 molecules NH 3 6. 02 x 1023 molecules N 2 + 1 mol N 2 + 3 mol H 2 2 mol NH 3 28 g N 2 1 x + 3 x 2 g H 2 2 x 17 g NH 3 3 x 6. 02 x 1023 molecules H 2 34 g reactants Assume STP 22. 4 L N 2 + 22. 4 L 67. 2 L H 2 22. 4 L 2 x 6. 02 x 1023 molecules NH 3 34 g products 22. 4 L 44. 8 L NH 3

Proportional Relationships 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. I have 5 eggs. How many cookies can I make? 5 eggs 5 doz. 2 eggs Ratio of eggs to cookies 150 cookies = 12. 5 dozen cookies Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Proportional Relationships • Stoichiometry – mass relationships between substances in a chemical reaction – based on the mole ratio • Mole Ratio – indicated by coefficients in a balanced equation 2 Mg + O 2 2 Mg. O Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Stoichiometry Steps 1. Write a balanced equation. 2. Identify known & unknown. 3. Line up conversion factors. – – – Mole ratio Molar mass Mole ratio - Molarity Molar volume - moles moles grams moles liters soln moles liters gas Core step in all stoichiometry problems!! 4. Check answer. Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Molar Volume at STP 1 mol of a gas=22. 4 L at STP Standard Temperature & 0°C and 1 atm Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem Pressure

Molar Volume at STP LITERS OF GAS AT STP Molar Volume (22. 4 L/mol) MASS IN GRAMS Molar Mass (g/mol) 6. 02 1023 MOLES particles/mol NUMBER OF PARTICLES Molarity (mol/L) LITERS OF SOLUTION Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Stoichiometry Problems How many moles of KCl. O 3 must decompose in order to produce 9 moles of oxygen gas? 2 KCl. O 3 2 KCl + 3 O 2 ? mol 9 mol O 2 9 mol 2 mol KCl. O 3 3 mol O 2 = 6 mol KCl. O 3 Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

How many moles of KCl. O 3 must decompose in order to produce 9 moles of oxygen gas? 2 KCl. O 3 2 KCl + 3 O 2 ? mol 9 mol O 2 9 mol 2 mol KCl. O 3 3 mol O 2 x mol KCl. O 3 = 9 mol O 2 2 mol KCl. O 3 3 mol O 2 = 6 mol KCl. O 3 6 mol = 6 mol KCl. O 3 Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Stoichiometry Problems How many grams of KCl. O 3 are required to produce 9. 00 L of O 2 at STP? 2 KCl. O 3 2 KCl + 3 O 2 ? g 9. 00 L O 2 1 mol O 2 2 mol 122. 55 KCl. O 3 g KCl. O 3 22. 4 L O 2 3 mol O 2 1 mol KCl. O 3 Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem = 32. 8 g KCl. O 3

Stoichiometry Problems How many grams of KCl. O 3 are required to produce 9. 00 L of O 2 at STP? 2 KCl. O 3 2 KCl + 3 O 2 ? g 9. 00 L x g KCl. O 3 = 9. 00 L O 2 1 mol O 2 22. 4 L O 2 32. 8 g 2 mol KCl. O 3 122. 55 g KCl. O 3 = 32. 8 g KCl. O 3 3 mol O 2 1 mol KCl. O 3 Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

How many grams of KCl. O 3 are required to produce 9. 00 L of O 2 at STP? 2 KCl. O 3 2 KCl + 3 O 2 ? g 9. 00 L O 2 1 mol O 2 2 mol 122. 55 KCl. O 3 g KCl. O 3 22. 4 L O 2 3 mol O 2 x g KCl. O 3 = 9. 00 L O 2 1 mol O 2 22. 4 L O 2 1 mol KCl. O 3 = 32. 8 g KCl. O 3 32. 8 g 2 mol KCl. O 3 122. 55 g KCl. O 3 = 32. 8 g KCl. O 3 3 mol O 2 1 mol KCl. O 3 Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

How many grams of silver will be formed from 12. 0 g copper? Cu + 2 Ag. NO 3 2 Ag + Cu(NO 3)2 12. 0 g Cu ? g 1 mol Cu 2 mol Ag 107. 87 g Ag 63. 55 g Cu 1 mol Ag x g Ag = 12. 0 g Cu Cu = 40. 7 g Ag 2 mol Ag 107. 87 g Ag 1 mol Cu 1 mol Ag 63. 55 g Cu 1 mol Cu Ag Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem 40. 7 g = 40. 7 g Ag

Mole Calculations A graduated cylinder holds 25. 4 cm 3 of mercury. If the density of mercury at 25 o. C is 13. 534 g / cm 3, how many moles of mercury are in the cylinder? How many atoms of mercury are there? HINT: Volume of solids/liquids and moles are not directly connected. You must first use the density to convert the volume to a mass, and then derive the quantity of mercury, in moles, from the mass. Finally, the number of atoms is obtained from the number of moles. x Volume, cm 3 g cm 3 use density x Mass, g Kotz & Treichel, Chemistry & Chemical Reactivity, 3 rd Edition , 1996, page 93 mol g use molar mass x Moles atoms mol use Avogadro’s number Atoms

A x Volume, cm 3 g cm 3 use density B x Mass, g C mol g x use molar mass Moles atoms mol use Avogadro’s number Atoms A Therefore, the mass of mercury is found to be equivalent to 344 g of mercury. 25. 4 cm 3 Hg. 13. 534 g Hg = 1 cm 3 Hg 344 g Hg B Knowing the mass, you can now find the quantity in moles. 344 g Hg. 1 mol Hg. = 200. 6 g Hg 1. 71 mol Hg C Finally, because you know the relation between atoms and moles (Avogodro’s number), you can now holds 25. 4 cm 3 of mercury. If the density of mercury A graduated cylinder find the number of atoms in the sample. at 25 o. C is 13. 534 g / cm 3, how many moles of mercury are in the cylinder? How many mol Hgof mercury 1023 there? Hg. 1. 71 atoms. 6. 02 x are atoms = 1. 03 x 1024 atoms Hg 1 mol Hg Kotz & Treichel, Chemistry & Chemical Reactivity, 3 rd Edition , 1996, page 93

2 Na + Cl 2 2 Na. Cl x. L 1 gram 100 g 2 grams xg 2 grams WRONG Violates Law of Conservation of Matter 2 atoms = 100 g Na 1 molecule x L Cl 2 23 g Na Na Cl 2 2 moles 1 mole 1 mol Cl 2 222. 4 L Cl 2 molecules* = 49 L Cl. L 48. 69 2 2 mol Na 1 mol Cl 2 2 moles Right side of room…calculate how many grams of Na. Cl will be produced from 100 g of Na. x g Na. Cl = 100 g Na Na 1 mol Na 23 g Na 2 mol Na. Cl 58. 5 g Na. Cl = 254 g Na. Cl 2 mol Na 1 mol Na. Cl Left side of room…calculate how many grams of Na. Cl will be produced from 48. 69 L of Cl 2. x g Na. Cl = 48. 69 L Cl 2 Na. Cl *Better name would be “formula unit” 1 mol Cl 2 22. 4 L Cl 2 2 mol Na. Cl 58. 5 g Na. Cl = 254 g Na. Cl 1 mol Cl 2 1 mol Na. Cl

Stoichiometry 2 KCl. O 3 2 KCl 500 g xg x L O 2 = 500 g KCl. O 3 x. L (196 g) 3 mol O 2 22. 4 L O 2 1 mol KCl. O 3 137 = 137 LLO 2 122. 5 g KCl. O 3 2 mol KCl. O 3 1 mol O 2 x g O 2 = 137 L O 2 1 mol O 2 32 g O 2 = 196 g O 2 22. 4 L O 2 1 mol O 2 x g KCl = 500 g KCl. O 3 + 3 O 2 KCl 2 mol KCl 74. 5 g KCl 1 mol KCl. O 3 (304 KCl = 304 gg) 122. 5 g KCl. O 3 2 mol KCl. O 3 1 mol KCl

Stoichiometry 2 Ti. O 2 + 4 Cl 2 + 3 C 115 g xg x mol CO 2 + 2 CO + 2 Ti. Cl 4 4. 55 mol x molecules How many moles of chlorine will react with 4. 55 moles of carbon? x mol Cl 2 = 4. 55 mol C C 4 mol Cl 2 3 mol C = 6. 07 mol C Cl 2 How many grams of titanium (IV) oxide will react with 4. 55 moles of carbon? x g Ti. O 2 = 4. 55 mol C C 2 mol Ti. O 2 80 g Ti. O 2 1 mol Ti. O 2 3 mol C = 243 g Ti. O 2 How many molecules of Ti. Cl 4 will react with 115 g Ti. O 2? x molecules Ti. Cl 4 = 115 g Ti. O 2 1 mol Ti. O 2 2 mol Ti. Cl 4 6. 02 x 1023 molecules Ti. Cl 4 1 mol Ti. Cl 4 80 g Ti. O 2 2 mol Ti. O 2 = 8. 66 x 1023 molecules Ti. Cl 4 Ti. O 2 Ti. Cl 4

Which has more atoms: 30 g aluminum metal or 18 m. L distilled water? How many atoms of aluminum are in 30 g of aluminum? 1 mol Al x atoms Al = 30 g Al 27 g Al 6. 02 x 1023 atoms Al = 6. 69 x 1023 atoms Al 1 mol Al Al 6. 02 x 1023 atoms Al x atoms Al = 30 g Al = 6. 69 x 1023 atoms Al 27 g Al Al How many atoms are in 18 m. L of water? W R O N G H 2 3 atoms 6. 02 x 1023 atoms H 2 O 1 mol H 2 O 6. 02 x 10 O molecules H 2 O 1 L H 2 O x atoms = 18 m. L H 2 O 1 molecule H 2 O 1 mol H 2 O 1000 m. L H 2 O 22. 4 L H 2 O LITERS is ONLY used for GASES @ STP How many atoms are in 18 m. L of water? 1 g H 2 O 1 mol H 2 O 6. 02 x 1023 molecules H 2 O x atoms = 18 m. L H 2 O 18 g H 2 O 1 mo. L H 2 O Recall, density of water = 1. 45 x 1021 atoms 3 atoms 1 molecule H 2 O = 1. 81 x 1024 atoms

Limiting Reactants + 48 tires 8 car bodies CB plus 16 tires excess + 4 T 8 cars CT 4

Limiting Reactants Methane, CH 4 + 24 hydrogen molecules 8 carbon atoms C plus 16 plus 8 hydrogen molecules atoms excess + 2 H 2 8 methane molecules CH 4

Container 1 Zumdahl, De. Coste, World of Chemistry 2002, page 269

Before and After Reaction 1 N 2 + 3 H 2 Before the reaction 2 NH 3 After the reaction All the hydrogen and nitrogen atoms combine. Zumdahl, De. Coste, World of Chemistry 2002, page 269

Container 2 Zumdahl, De. Coste, World of Chemistry 2002, page 270

Before and After Reaction 2 N 2 + 3 H 2 excess 2 NH 3 limiting Before the reaction After the reaction LIMITING REACTANT DETERMINES AMOUNT OF PRODUCT Zumdahl, De. Coste, World of Chemistry 2002, page 270

Real-World Stoichiometry: Limiting Reactants Fe + S Fe. S Ideal Stoichiometry Limiting Reactants S = Fe = Le. May Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 366 excess

Grilled Cheese Sandwich Bread + 2 B + 100 bread Cheese C 30 slices ‘Cheese Melt’ B 2 C 30 sandwiches ? Multiple Guess: 130 sandwiches 100 sandwiches 90 sandwiches 60 sandwiches 30 sandwiches Not enough information given

Limiting Reactants • Available Ingredients – 4 slices of bread – 1 jar of peanut butter – 1/2 jar of jelly • Limiting Reactant – bread • Excess Reactants – peanut butter and jelly Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Limiting Reactants • Limiting Reactant – used up in a reaction – determines the amount of product • Excess Reactant – added to ensure that the other reactant is completely used up – cheaper & easier to recycle Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

The Limiting Reactant A balanced equation for making a Big Mac® might be: 3 B + 2 M + EE B 3 M 2 EE With… …and… …one can make… 30 M excess B and excess EE 15 B 3 M 2 EE 30 B excess M and excess EE 10 B 3 M 2 EE 30 M 30 B and excess EE 10 B 3 M 2 EE

The Limiting Reactant A balanced equation for making a tricycle might be: 3 W + 2 P + S + H + F W 3 P 2 SHF With… …and… …one can make… 50 P excess of all other reactants 25 W 3 P 2 SHF 50 S excess of all other reactants 50 W 3 P 2 SHF 50 P 50 S and excess of all other reactants 25 W 3 P 2 SHF

Limiting Reactants aluminum + chlorine gas Al(s) + Cl 2(g) Al. Cl 3 2 Al(s) + 3 Cl 2(g) 2 Al. Cl 3 100 g A. 200 g aluminum chloride 100 g B. 125 g ? g C. 667 g D. 494 g

Limiting Reactants aluminum 2 Al(s) 100 g + + chlorine gas 3 Cl 2(g) 100 g aluminum chloride 2 Al. Cl 3 xg How much product would be made if we begin with 100 g of aluminum? x g Al. Cl 3 = 100 g Al Al 1 mol Al 27 g Al 2 mol Al. Cl 3 133. 5 g Al. Cl 3 2 mol Al 1 mol Al. Cl 3 = 494 g Al. Cl 3 How much product would be made if we begin with 100 g of chlorine gas? x g Al. Cl 3 = 100 g Cl 2 Al. Cl 3 1 mol Cl 2 71 g Cl 2 2 mol Al. Cl 3 133. 5 g Al. Cl 3 3 mol Cl 2 1 mol Al. Cl 3 = 125 g Al. Cl 3

Limiting Reactants – Method 1 1. Write a balanced equation. 2. For each reactant, calculate the amount of product formed. 3. Smaller answer indicates: – limiting reactant – amount of product Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

Limiting Reactants – Method 2 • Begin by writing a correctly balanced chemical equation • Write down all quantitative values under equation (include units) • Convert ALL reactants to units of moles • Divide by the coefficient in front of each reactant • The smallest value is the limiting reactant!

Generic Stoichiometry Z (aq) + 2 Y (aq) 5 M (s) + T 2 (g) Given the following information: Z = 20 g/mol Y = 10 g/mol M = 6 g/mol T = 5 g/mol If you combine 100 g of solution Z with 1. 8 x 1024 molecules of solution Y: How many moles of M will precipitate out of the solution? What volume of T 2 gas will be produced at STP?

LIMITING EXCESS Z (aq) + 100 g 2 Y (aq) 5 M (s) x mol 7. 5 mol M 1. 8 x 1024 molecules / 6. 02 x 1023 molecules/mol / 20 g /mol + T 2(g) 33. 6 L T 2 2 5 = 3 mol Y x mol M x 22. 4 L/mol 15 = 2 x 2 : 5 HAVE 5 mol Z 3 mol Y NEED 1 1. 5 mol Z 5 mol 2 10 mol Y 1. 5 mol Easy x = 7. 5 mol 1. 5 mol T 2 2 : 1 SMALLER Number is LIMITING Reactant EXCESS x mol M = 1. 8 x 1024 molecules Y x L T 2 = 3 mol Y 1 mol T 2 2 mol Y 1 mol Y 6. 02 x 1023 molecules Y 22. 4 L T 2 = 33. 6 L T 2 1 mol T 2 5 mol M 2 mol Y = 7. 5 mol M

Z (aq) + 2 Y (aq) 1. 8 x 1024 molecules 5 M (s) x mol 3 mol Y x mol M = 3 mol Y Y M 5 mol M 2 mol Y = 7. 5 mol M + T 2(g)

Stoichiometry in the Real World

Air Bag Design • Exact quantity of nitrogen gas must be produced in an instant. • Use a catalyst to speed up the reaction 2 Na. N 3(s) 2 Na(s) + 3 N 2(g) 6 Na(s) + Fe 2 O 3(s) 3 Na 2 O(s) + 2 Fe (s)

2 Na. N 3(s) 2 Na(s) + 3 N 2(g) 6 Na(s) + Fe 2 O 3(s) 3 Na 2 O(s) + 2 Fe(s) Airbag Design Assume that 65. 1 L of N 2 gas are needed to inflate an air bag to the proper size. How many grams of Na. N 3 must be included in the gas generant to generate this amount of N 2? (Hint: The density of N 2 gas at this temperature is about 0. 916 g/L). 65. 1 L N 2 x 0. 916 g/L N 2 x g Na. N 3 = 59. 6 g N 2 1 mol N 2 2 mol Na. N 3 65 g Na. N 3 28 g N 2 3 mol N 2 1 mol Na. N 3 X = 92. 2 g Na. N 3 How much Fe 2 O 3 must be added to the gas generant for this amount of Na. N 3? x g Fe 2 O 3 = 92. 2 g Na. N 3 1 mol Na. N 3 2 mol Na 1 mol Fe 2 O 3 159. 6 g Fe 2 O 3 65 g Na. N 3 2 mol Na. N 3 6 mol Na 1 mol Fe 2 O 3 X = 37. 7 g Fe 2 O 3

Water from a Camels store the fat tristearin (C 57 H 110 O 6) in the hump. As well as being a source of energy, the fat is a source of water, because when it is used the reaction 2 C 57 H 110 O 6(s) + 163 O 2(g) 114 CO 2(g) + 110 H 2 O(l) takes place. What mass of water can be made from 1. 0 kg of fat? x g H 2 O = 1 kg ‘fat” 1000 g “fat” 1 mol “fat” 110 mol H 2 O 18 g H 2 O 1 kg “fat” 890 g “fat” 2 mol “fat” 1 mol H 2 O X = 1112 g H 2 O or 1. 112 liters water

Rocket Fuel The compound diborane (B 2 H 6) was at one time considered for use as a rocket fuel. How many grams of liquid oxygen would a rocket have to carry to burn 10 kg of diborane completely? (The products are B 2 O 3 and H 2 O). B 2 H 6 + O 2 Chemical equation Balanced chemical equation B 2 H 6 + O 2 B 2 O 3 + H 2 O 3 3 10 kg x g O 2 = 10 kg B 2 H 6 B 2 O 3 + H 2 O xg 1000 g B 2 H 6 1 mol B 2 H 6 1 kg B 2 H 6 28 g B 2 H 6 3 mol O 2 32 g O 2 1 mol B 2 H 6 1 mol O 2 X = 34, 286 g O 2

Water in Space Click Here In the space shuttle, the CO 2 that the crew exhales is removed from the air by a reaction within canisters of lithium hydroxide. On average, each astronaut exhales about 20. 0 mol of CO 2 daily. What volume of water will be produced when this amount of CO 2 reacts with an excess of Li. OH? (Hint: The density of water is about 1. 00 g/m. L. ) CO 2(g) + 2 Li. OH(s) Li 2 CO 3(aq) + H 2 O(l) 20. 0 mol xg excess x m. L H 2 O = 20. 0 mol CO 2 Water is NOT at STP! 1 mol H 2 O 22. 4 g. LH 2 O 1 m. L H 2 O 18 H 2 O 1 mol CO 2 1 mol H 2 O 1 g H 2 O X = 360 m. L H 2 O

Lithium Hydroxide Scrubber Modified by Apollo 13 Mission Astronaut John L. Swigert holds the jury-rigged lithium hydroxide scrubber used to remove excess carbon dioxide from the damaged Apollo 13 spacecraft.

Real Life Problem Solving Determine the amount of Li. OH required for a seven-day mission in space for three astronauts and one ‘happy’ chimpanzee. Assume each passenger expels 20 mol of CO 2 per day. Note: The lithium hydroxide scrubbers are only 85% efficient. (4 passengers) x (10 days) x (20 mol/day) = 800 mol CO 2 Plan for a delay CO 2(g) + 2 Li. OH(s) Li 2 CO 3(aq) + H 2 O(l) 800 mol Xg

CO 2(g) + 2 Li. OH(s) Li 2 CO 3(aq) + H 2 O(l) 38, 240 g xg 800 mol x 23. 9 g/mol 800 mol 1: 2 1600 mol X g Li. OH = 800 mol CO 2 Needed (actual yield) 2 mol Li. OH 23. 9 g Li. OH = 38, 240 g Li. OH 1 mol CO 2 1 mol Li. OH Note: The lithium hydroxide scrubbers are only 85% efficient. % Yield = Actual Yield Theoretical Yield 0. 85 = Amount of Li. OH to be taken into space 38, 240 g Li. OH x = 44, 988 g Li. OH

Careers in Chemistry: Farming is big business in the United States with profits for the lucky and possible bankruptcy for the less fortunate. Farmers should not be ignorant of chemistry. For instance, to be profitable, a farmer must know when to plant, harvest, and sell his/her crops to maximize profit. In order to get the greatest yield farmers often add fertilizers to the soil to replenish vital nutrients removed by the previous season’s crop. Corn is one product that removes a tremendous amount of phosphorous from the soil. For this reason, farmers will rotate crops and/or add fertilizer to the ground before planting crops for the following year. On average, an acre of corn will remove 6 kilograms of phosphorous from the ground. Assume you inherit a farm and must now have to purchase fertilizer for the farm. The farm is 340 acres and had corn planted the previous year. You must add fertilizer to the soil before you plant this years’ crop. You go to the local fertilizer store and find Super. Phosphate. TM brand fertilizer. You read the fertilizer bag and can recognize from your high school chemistry class a molecular formula Ca 3 P 2 H 14 S 2 O 21 (you don’t understand anything else written on the bag because it is imported fertilizer from Japan). You must decide how much fertilizer to buy for application to your corn fields. If each bag costs $54. 73; how many bags of fertilizer must you purchase and how much will it cost you to add the necessary fertilizer to your fields? Given: 1 bag of fertilizer weighs 10, 000 g [454 g = 1 pound]

Careers in Chemistry: Farming How much fertilizer will you need? Conversion Factor: 1 acre corn = 6 kg phosphorous x g P = 340 acres 6 kg P 1 acre 1000 g P 1 kg P = 2. 04 x 106 g P If a bag of fertilizer has the formula Ca 3 P 2 H 14 S 2 O 21, The molar mass of it is 596 g/mol. 3 Ca @ 40 g/mol 2 P@ 31 g/mol 14 H@ 1 g/mol 2 S@ 32 g/mol 21 O @ 16 g/mol Ca 3 P 2 H 14 S 2 O 21 = 120 g = 62 g = 14 g = 64 g = 335 g = 596 g %P = 10. 4 % Phosphorous In a bag of fertilizer you have 10. 4 % (by mass) phosphorous. A bag of fertilizer weighs 10, 000 g (about 22 pounds). 10. 4 % of 10, 000 g = 1040 g phosphorous / bag of fertilizer 2. 04 x 106 g P = 1962 bags of fertilizer 1040 g/bag Total Cost (1962 bags of fertilizer)($54. 73 / bag) = $107, 380 part 62 g x 100 % whole 596 g

Careers in Chemistry: Dentistry We learned that fluoride is an essential element to be taken to reduce teeth cavities. Too much fluoride can produce yellow spots on the teeth and too little will have no effect. After years of study it was determined that a quantity of 1 part per million (ppm) fluoride in the water supply is enough to significantly reduce cavities and not stain teeth yellow. Measure the mass of the mineral fluorite (chemically, Ca. F 2). Use this sample to determine how much water must be added to yield a 1 ppm fluoride solution. Sounds difficult? Lets apply what we’ve learned this unit to solve this problem. 1 part per million = 1 atom of fluorine per 999, 999 water molecules What information do we know: 1 mol Ca. F 2 = 78. 08 g Ca. F 2 = 6. 02 x 1023 molecules of Ca. F 2 1 molecules of Ca. F 2 = 2 atoms of F 1 mol H 2 O = 18 g H 2 O Density of water is 1 g/m. L 1000 m. L = 1 L and 3. 78 L = 1 gallon mass of sample of Ca. F 2 = 92. 135 g

Careers in Chemistry: Dentistry Calcium Fluoride x atoms F = 92. 135 g Ca. F 2 x gallons H 2 O = 1. 42 x 1024 F atoms Need 1 mol Ca. F 2 6. 02 x 1023 molecules Ca. F 2 2 atoms F 78 g Ca. F 2 1 molecules Ca. F 2 999, 999 H 2 O molecules 1 F atom 11, 238 gallons of water 1 mol H 2 O 18 g H 2 O 6. 02 x 1023 H 2 O molecules 1 mol H 2 O needed to dissolve 91. 235 g Ca. F 2 = 1. 42 x 1024 atoms F 1 m. L H 2 O 1 gallon H 2 O 1 g H 2 O 1000 m. L H 2 O 3. 78 L H 2 O to yield a 1 ppm F 1 - solution. =

Energy with Stoichiometry Given: 1 mol O 2 yields 350 k. J 350 k. J methane ? oxygen + carbon dioxide + water + energy Limiting Excess + CH 4 2 O 2 100 g CO 2 + 700 k. J ? k. J 100 g / 32 g/mol / 16 g/mol x k. J = 3. 125 mol O 2 6. 25 mol CH 1 3. 125 mol O 6. 25 1. 56 4 2 H 2 O + 2 smaller number is limiting reactant 2 700 k. J = 1094 k. J 2 mol O 2

Visualizing Limiting Reactant 2 2 H 2 + O 2 H 2 O 7 0 8 3 4 2 6 5 1 ___ mole H 2 2. 5 1. 5 4. 5 3. 5 1 5 3 2 4 ___ mole O 2 Limiting Reactant Excess 1 5 8 0 4 6 2 3 7 ___ mole H 2 O Limiting reactant determines amount of product.

Excess Reactant 2 Na + 50 g / 23 g/mol “Have” 2. 17 mol Cl 2 / 71 g/mol 0. 70 mol LIMITING 2 Na. Cl 81. 9 x g g Na. Cl 50 g “Need” 1. 40 mol EXCESS 1: 2 coefficients x 58. 5 g/mol 1. 40 mol

Excess Reactant (continued) excess 2 Na limiting + Cl 2 50 g 2 Na. Cl 81. 9 x g g Na. Cl All the chlorine is used up… 81. 9 g Na. Cl -50. 0 g Cl 2 31. 9 g Na is consumed in reaction. How much Na is unreacted? 50. 0 g - 31. 9 g = 18. 1 g Na total used “excess”

Conservation of Mass is Obeyed 2 Na + 50 g 2 Na Cl 2 81. 9 x g g Na. Cl 50 g + 50 g Cl 2 50 g 2 Na. Cl + Na 81. 9 x g g Na. Cl 18. 1 g 31. 9 g + 18. 1 g 100 81. 9 g product 100 81. 9 g reactant

Solid aluminum react with chlorine gas to yield solid aluminum chloride. 2 Al(s) excess 125 g + 3 Cl 2(g) excess 125 g 2 Al. Cl 3(s) xg If 125 g aluminum react with excess chlorine, how many grams of aluminum chloride are made? x g Al. Cl 3 = 125 g Al Al 1 mol Al 2 mol Al. Cl 3 133. 5 g Al. Cl 3 = 618 g Al. Cl 3 2 mol Al 1 mol Al. Cl 3 27 g Al Al. Cl 3 If 125 g chlorine react with excess aluminum, how many grams of aluminum chloride are made? x g Al. Cl 3 = 125 g Cl 2 1 mol Cl 2 2 mol Al. Cl 3 133. 5 g Al. Cl 3 = 157 g Al. Cl 3 3 mol Cl 2 1 mol Al. Cl 3 71 g Cl 2 Al. Cl 3 If 125 g aluminum react with 125 g chlorine, how many grams of aluminum chloride are made? 157 g Al. Cl 3 We’re out of Cl 2

Solid aluminum react with chlorine gas to yield solid aluminum chloride. If 125 g aluminum react with excess chlorine, how many grams of aluminum chloride are made? 2 Al(s) + 125 g 3 Cl 2(g) 2 Al. Cl 3(s) 618 x g g Al. Cl 3 excess / 27 g/mol 4. 6 mol Al x 133. 5 g/mol 2: 2 Step 1 x g Al. Cl 3 = 125 g Al Al Al. Cl 3 4. 6 mol Al. Cl 3 Step 2 Step 3 1 mol Al 2 mol Al. Cl 3 133. 5 g Al. Cl 3 = 618 g Al. Cl 3 2 mol Al 1 mol Al. Cl 3 27 g Al

Solid aluminum react with chlorine gas to yield solid aluminum chloride. If 125 g chlorine react with excess aluminum, how many grams of aluminum chloride are made? 2 Al(s) excess + 3 Cl 2(g) 2 Al. Cl 3(s) 157 x g g Al. Cl 3 125 g / 71 g/mol 1. 76 mol Cl 2 x 133. 5 g/mol 3: 2 1. 17 mol Al. Cl 3 3 2 = 1. 76 mol Al x mol Al 3 x = 3. 52 x = 1. 17 mol Step 1 x g Al. Cl 3 = 125 g Cl 2 Al. Cl 3 Step 2 Step 3 1 mol Cl 2 2 mol Al. Cl 3 133. 5 g Al. Cl 3 = 157 g Al. Cl 3 3 mol Cl 2 1 mol Al. Cl 3 71 g Cl 2

Limiting Reactant Problems 1. According to the balanced chemical equation, how many atoms of silver will be produced from combining 100 g of copper with 200 g of silver nitrate? Easy Cu(s) + 2 Ag. NO 3(aq) Cu(NO 3)2(aq) + 2 Ag(s) 2. At STP, what volume of “laughing gas” (dinitrogen monoxide) will be produced from 50 g of nitrogen gas and 75 g of oxygen gas? Easy 3. Carbon monoxide can be combined with hydrogen to produce methanol, CH 3 OH. Methanol is used as an industrial solvent, as a reactant in some synthesis reactions, and as a clean-burning fuel for some racing cars. If you had 152 kg of carbon monoxide and 24. 5 kg of hydrogen gas, how many kilograms of methanol could be produced? Easy 4. How many grams of water will be produced from 50 g of hydrogen and 100 g of oxygen? Easy Answers: 1. 7. 1 x 1023 atoms Ag 2. 40 dm 3 N 2 O 3. 174. 3 kg CH 3 OH 4. 112. 5 g H 2 O

Limiting Reactant Problems 1. According to the balanced chemical equation, how many atoms of silver will be produced from combining 100 g of copper with 200 g of silver nitrate? Back Cu(s) + 2 Ag. NO 3(aq) Excess 100 g Limiting 200 g 1. 57 x atoms / 170 g/mol / 63. 5 g/mol 1. 57 mol Cu 1 Cu(NO 3)2(aq) + 2 Ag(s) 1. 18 mol Ag. NO 3 2 0. 59 smaller number is limiting reactant x atoms Ag = 1. 18 mol Ag. NO 3 2 mol Ag 6. 02 x 1023 atoms Ag 2 mol Ag. NO 3 1 mol Ag = 7. 1 x 1023 atoms Ag

Limiting Reactant Problems 2. At STP, what volume of “laughing gas” (dinitrogen monoxide) will be produced from 50 g of nitrogen gas and 75 g of oxygen gas? Back 2 N 2(g) + O 2(g) 2 N 2 O(g) Limiting 50 g Excess 75 g x. L / 32 g/mol / 28 g/mol 1. 79 mol N 2 2 2. 34 mol O 2 1 0. 89 2. 34 smaller number is limiting reactant x L N 2 O = 1. 79 mol N 2 2 mol N 2 O 22. 4 L N 2 O 2 mol N 2 1 mol N 2 O = 40 L N 2 O

Limiting Reactant Problems 3. Carbon monoxide can be combined with hydrogen to produce methanol, CH 3 OH. Methanol is used as an industrial solvent, as a reactant in some synthesis reactions, and as a clean-burning fuel for some racing cars. If you had 152 kg of carbon monoxide and 24. 5 kg of hydrogen gas, how many kilograms of methanol could be produced? Back CO (g) + 2 H 2(g) Limiting 152. 5 g CH 3 OH (g) Excess 24. 5 g xg 174. 3 kg / 2 g/mol / 28 g/mol 5. 45 mol CO 1 12. 25 mol H 2 2 5. 45 Work the entire problem with the mass in grams. At the end, change answer to units of kilograms. 6. 125 smaller number is limiting reactant x g CH 3 OH = 5. 45 mol CO 1 mol CH 3 OH 1 mol CO 32 g CH 3 OH 1 mol CH 3 OH = 174. 3 g CH 3 OH

Limiting Reactant Problems 4. How many grams of water will be produced from 50 g of hydrogen and 100 g of oxygen? Back 2 H 2(g) + Excess 50 g O 2(g) 2 H 2 O(g) Limiting 100 g xg / 32 g/mol / 2 g/mol 25 mol H 2 2 3. 125 mol O 2 1 12. 5 3. 125 smaller number is limiting reactant x g H 2 O = 3. 125 mol O 2 2 mol H 2 O 18 g H 2 O 1 mol O 2 1 mol H 2 O = 112. 5 g H 2 O

Limiting Reactant Problems - continued 2 5. An unbalanced chemical equation is given as __N 2 H 4(l) + __N 2 O 4(l) If you begin with 400 g of N 2 H 4 and 900 g of N 2 O 4… 3 4 __N 2(g) + __ H 2 O(g). Easy A. Find the number of liters of water produced (at STP), assuming the reaction goes to completion. Easy B. Find the number of liters of nitrogen produced at STP, assuming the reaction goes to completion. Easy C. Find the mass of excess reactant left over at the conclusion of the reaction. 4 6. An unbalanced chemical equation is given as __Na(s) + __O 2(g) If you have 100 g of sodium and 60 g of oxygen… 2 __Na 2 O (s) Easy A. Find the number of moles of sodium oxide produced. Easy B. Find the mass of excess reactant left over at the conclusion of the reaction. Answers: 5 A. 560 L H 2 O (@STP - gas) or 0. 45 L H 2 O 5 B. 420 L N 2 5 C. 325 g N 2 O 4 excess 6 A. 2. 17 mol Na 2 O 6 B. 25. 2 g O 2 excess

Limiting Reactant Problems 5. An unbalanced chemical equation is given as __N 2 H 4(l) + __N 2 O 4(l) 2 If you begin with 400 g of N 2 H 4 and 900 g of N 2 O 4… __N 2(g) + __ H 2 O(g). 3 4 A. Find the number of liters of water produced at STP, assuming the reaction goes to completion. Back 2 N 2 H 4(l) + N 2 O 4(l) 400 g 6. 25 x. L 900 g / 92 g/mol / 32 g/mol 12. 5 mol N 2 H 4 2 3 N 2(g) + 4 H 2 O(g) 9. 78 mol N 2 O 4 1 9. 78 smaller number is limiting reactant Water is a SOLIDwater Density of at STP … this is 1. 0 g/m. L isn’t possible! 4 mol H 2 O 22. 4 L H 2 O 4 mol H 2 O 18 g H 2 O 1 m. L H 2 O = 560 L H 2 O 1 L H 2 O x L H 2 O = 12. 5 mol N 2 H 4 = 0. 45 L H 2 O x L H 2 O = 12. 5 mol N 2 H 4 2 mol N 2 H 4 1 mol H 2 O 1. 0 g H 2 O 1000 m. L H 2 O

Limiting Reactant Problems 5. An unbalanced chemical equation is given as __N 2 H 4(l) + __N 2 O 4(l) 2 If you begin with 400 g of N 2 H 4 and 900 g of N 2 O 4… __N 2(g) + __ H 2 O(l). 3 4 A. Find the number of liters of water produced, assuming the reaction goes to completion. Back 2 N 2 H 4(l) + N 2 O 4(l) 400 g x. L 900 g / 92 g/mol / 32 g/mol 12. 5 mol N 2 H 4 2 3 N 2(g) + 4 H 2 O(g) 9. 78 mol N 2 O 4 1 6. 25 Density of water is 1. 0 g/m. L 9. 78 smaller number is limiting reactant x L H 2 O = 12. 5 mol N 2 H 4 4 mol H 2 O 18 g H 2 O 1 m. L H 2 O 1 L H 2 O 2 mol N 2 H 4 1 mol H 2 O 1. 0 g H 2 O 1000 m. L H 2 O = 0. 45 L H 2 O

Limiting Reactant Problems 5. An unbalanced chemical equation is given as __N 2 H 4(l) + __N 2 O 4(l) 2 If you begin with 400 g of N 2 H 4 and 900 g of N 2 O 4… __N 2(g) + __ H 2 O(g). 3 4 B. Find the number of liters of nitrogen produced at STP, assuming the reaction goes to completion. Back 2 N 2 H 4(l) + N 2 O 4(l) 400 g 6. 25 x. L 900 g / 92 g/mol / 32 g/mol 12. 5 mol N 2 H 4 2 3 N 2(g) + 4 H 2 O(g) 9. 78 mol N 2 O 4 1 9. 78 smaller number is limiting reactant x L N 2 = 12. 5 mol N 2 H 4 3 mol N 2 22. 4 L N 2 2 mol N 2 H 4 1 mol N 2 = 420 L N 2

Limiting Reactant Problems 5. An unbalanced chemical equation is given as __N 2 H 4(l) + __N 2 O 4(l) 2 If you begin with 400 g of N 2 H 4 and 900 g of N 2 O 4… __N 2(g) + __ H 2 O(g). 3 4 C. Find the mass of excess reactant left over at the conclusion of the reaction. Back 2 N 2 H 4(l) + N 2 O 4(l) 400 g 575 g xg / 32 g/mol 12. 5 mol N 2 H 4 N 2(g) + H 2 O(g) x 92 g/mol 900 g N 2 O 4 have needed 325 g N 2 O 4 excess 6. 25 mol N 2 O 4 x g N 2 O 4 = 12. 5 mol N 2 H 4 1 mol N 2 O 4 92 g N 2 O 4 2 mol N 2 H 4 1 mol N 2 O 4 = 575 g N 2 O 4

Limiting Reactant Problems 6. An unbalanced chemical equation is given as __Na(s) + __O 2(g) 4 If you have 100 g of sodium and 60 g of oxygen… Back __Na 2 O (s) 2 A. Find the number of moles of sodium oxide produced. 4 Na(s) + 100 g O 2 (g) 2 Na 2 O (s) x mol 60 g / 32 g/mol / 23 g/mol 4. 35 mol Na 4 1. 875 mol O 2 1 1. 087 1. 875 smaller number is limiting reactant x mol Na 2 O = 4. 35 mol Na 2 O 4 mol Na = 2. 17 mol Na 2 O

Limiting Reactant Problems 6. An unbalanced chemical equation is given as __Na(s) + __O 2(g) 4 If you have 100 g of sodium and 60 g of oxygen… __Na 2 O (s) 2 B. Find the mass of excess reactant left over at the conclusion of the reaction. Back 4 Na(s) + 100 g O 2 (g) 2 Na 2 O (s) 34. 8 g xg / 23 g/mol x 32 g/mol - 60 g O 2 25. 2 g O 2 4. 35 mol Na have needed excess 1. 087 mol O 2 x g O 2 = 4. 35 mol Na 1 mol O 2 32 g O 2 4 mol Na 1 mol O 2 = 34. 8 g O 2

Percent Yield measured in lab % yield = actual yield theoretical yield calculated on paper x 100

When 45. 8 g of K 2 CO 3 react with excess HCl, 46. 3 g of KCl are formed. Calculate theoretical and % yields of KCl. actual yield 46. 3 g K 2 CO 3 + 2 HCl 45. 8 g excess 2 KCl + H 2 O +3 CO 2 CO ? g theoretical yield Theoretical yield x g KCl = 45. 8 g K 2 CO 3 % Yield = 1 mol K 2 CO 3 2 mol KCl 74. 5 g KCl = 49. 4 g KCl 1 mol K 2 CO 3 1 mol KCl 138 g K 2 CO 3 Actual Yield Theoretical Yield % Yield = 46. 3 g KCl x 100 % Yield = 93. 7% efficient

Percent Yield Need 500 g of Y …% yield = 80% actual yield 500 g 0. 80 % 80 == yield xg theoretical yield x 100 % actual yield W 2 + 2 X x atoms Y 0. 80 x = 500 g 0. 80 x = 625 g xg x L @STP theoretical yield x atoms W = 625 g Y x L X = 625 g Y 1 mol W 2 6. 02 x 1023 molecules W 2 89 g Y 1 mol W 2 1 mol Y 2 mol X 22. 4 L X 89 g Y 1 mol X 2 atoms W 1 molecule W 2 315 L X x 10 = 315 L X 8. 45 1024 atoms W W 8. 45 x atoms 24

Cartoon courtesy of Nearing. Zero. net

Print Copy of Lab Baking Soda Lab Na. HCO 3 + HCl sodium bicarbonate + H 2 CO 3 hydrochloric acid sodium chloride baking soda table salt D (l) H 2 O (g) + heat CO 2 (g) actual yield ? g Na. HCO 3 + HCl 5 g excess D actual yield theoretical yield gas Na. Cl + H 2 O + CO 2 xg theoretical yield % yield = gas x 100 %

Resources - Stoichiometry Objectives - stoichiometry Objectives - mole / chemical formula Lab – nuts and bolts Lab - baking soda lab Episode 11 – The Mole S’mores activity Worksheet - careers in chemistry: farming key Worksheet - careers in chemistry: dentistry key Worksheet - easy stoichiometry Worksheet - energy Worksheet - generic Worksheet – moles and mass relationships Worksheet - percent yield Worksheet - stoichiometry problems 1 Worksheet - limiting reactants Worksheet - vocabulary Worksheet - lecture outline Textbook - questions Worksheet – visualizing limiting reactant Outline (general)