1 STOICHIOMETRY TUTORIAL

2 Instructions: This is a work along tutorial. Each time you click the mouse or touch the space bar on your computer, one step of the problem solving occurs. Pressing the PAGE UP key will backup the steps. Get a pencil and paper, a periodic table and a calculator, and let’s get to work.

3 (1-2-3) General Approach For Problem Solving: 1. Clearly identify the Goal or Goals and the UNITS involved. (What are you trying to do?) 2. Determine what is given and the UNITS. 3. Use conversion factors (which are really ratios) and their UNITS to CONVERT what is given into what is desired.

4 Table of Contents: Click on each tab to view problem types. Sample problem 1 Sample problem 2 Converting grams to moles Mole to Mole Conversions View Complete Slide Show Gram-Mole and Gram-Gram Problems Solution Stoichiometry Problems Limiting/Excess/ Reactant and Theoretical Yield Problems :

5 Sample problem for general problem solving. Sam has entered into a 10 mile marathon. Use ALL of the following conversions (ratios) to determine how many inches there are in the race ft = 1 mile; 12 inches = 1 ft 1. What is the goal and what units are needed? Goal = ______ inches 2. What is given and its units? 10 miles 3. Convert using factors (ratios). 10 miles = inches Units match Given Goal Convert Menu

6 Sample problem #2 on problem solving. A car is traveling at a speed of 45 miles per hr (45 miles/hr). Determine its speed in kilometers per second using the following conversion factors (ratios). 1 mile = 5280 ft; 1 ft = 12 in; 1 inch = 2.54 cm; k = 1 x 10 3 ; c = 1 x ; 1 hr =60 min; 1 min = 60 s = km s Units Match! Goal c cancels c m remains Given This is the same as putting k over k

7 Converting grams to moles. Determine how many moles there are in 5.17 grams of Fe(C 5 H 5 ) 2. Goal = moles Fe(C 5 H 5 ) 2 Given 5.17 g Fe(C 5 H 5 ) 2 Use the molar mass to convert grams to moles. Fe(C 5 H 5 ) 2 2 x 5 x = x 5 x = x = units match

8 Stoichiometry (more working with ratios) Ratios are found within a chemical equation. 2HCl + Ba(OH) 2  2H 2 O + BaCl moles of HCl react with 1 mole of Ba(OH) 2 to form 2 moles of H 2 O and 1 mole of BaCl 2 coefficients give MOLAR RATIOS

9 When N 2 O 5 is heated, it decomposes: 2N 2 O 5 (g)  4NO 2 (g) + O 2 (g) a. How many moles of NO 2 can be produced from 4.3 moles of N 2 O 5 ? = moles NO mol N2O5N2O5 8.6 b. How many moles of O 2 can be produced from 4.3 moles of N 2 O 5 ? = mole O mol N2O5N2O N 2 O 5 (g)  4NO 2 (g) + O 2 (g) 4.3 mol? mol 2N 2 O 5 (g)  4NO 2 (g) + O 2 (g) 4.3 mol ? mol Mole – Mole Conversions Units match

10 When N 2 O 5 is heated, it decomposes: 2N 2 O 5 (g)  4NO 2 (g) + O 2 (g) a. How many moles of N 2 O 5 were used if 210g of NO 2 were produced? = moles N 2 O g NO b. How many grams of N 2 O 5 are needed to produce 75.0 grams of O 2 ? = grams N 2 O g O2O2 506 gram ↔ mole and gram ↔ gram conversions 2N 2 O 5 (g)  4NO 2 (g) + O 2 (g) 210g? moles 2N 2 O 5 (g)  4NO 2 (g) + O 2 (g) 75.0 g ? grams Units match

11 Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? First write a balanced equation. Al(s) + HCl(aq)  AlCl 3 (aq) + H 2 (g) Gram to Gram Conversions

12 Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq)  AlCl 3 (aq) + H 2 (g) Now let’s get organized. Write the information below the substances g ? grams Gram to Gram Conversions

13 Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq)  AlCl 3 (aq) + H 2 (g) g ? grams Let’s work the problem. = g AlCl g Al We must always convert to moles.Now use the molar ratio.Now use the molar mass to convert to grams Units match gram to gram conversions

14 Molarity Molarity is a term used to express concentration. The units of molarity are moles per liter (It is abbreviated as a capital M) When working problems, it is a good idea to change M into its units.

15 A solution is prepared by dissolving 3.73 grams of AlCl 3 in water to form mL solution. A 10.0 mL portion of the solution is then used to prepare mL of solution. Determine the molarity of the final solution. What type of problem(s) is this? Molarity followed by dilution. Solutions

16 A solution is prepared by dissolving 3.73 grams of AlCl 3 in water to form mL solution. A 10.0 mL portion of the solution is then used to prepare mL of solution. Determine the molarity of the final solution. 1 st : = mol L 3.73 g x L nd : M 1 V 1 = M 2 V 2 (0.140 M)(10.0 mL) = (? M)(100.0 mL) M = M 2 molar mass of AlCl 3 dilution formula final concentration Solutions

mL of 6.0 M H 2 SO 4 (battery acid) were spilled and solid NaHCO 3 (baking soda) is to be used to neutralize the acid. How many grams of NaHCO 3 must be used? H 2 SO 4 (aq) + 2NaHCO 3  2H 2 O(l) + Na 2 SO 4 (aq) + 2CO 2 (g) Solution Stoichiometry

mL 6.0 M ? g Look! A conversion factor! 50.0 mL of 6.0 M H 2 SO 4 (battery acid) were spilled and solid NaHCO 3 (baking soda) is to be used to neutralize the acid. How many grams of NaHCO 3 must be used? H 2 SO 4 (aq) + 2NaHCO 3  2H 2 O(l) + Na 2 SO 4 (aq) + 2CO 2 (g) Solution Stoichiometry = Our Goal

mL 6.0 M ? g 50.0 mL of 6.0 M H 2 SO 4 (battery acid) were spilled and solid NaHCO 3 (baking soda) is to be used to neutralize the acid. How many grams of NaHCO 3 must be used? H 2 SO 4 (aq) + 2NaHCO 3  2H 2 O(l) + Na 2 SO 4 (aq) + 2CO 2 (g) Solution Stoichiometry = Our Goal = g NaHCO 3 H 2 SO mL 1 mol H 2 SO 4 NaHCO 3 2 mol NaHCO g mol NaHCO

20 Solution Stoichiometry: Determine how many mL of M NaOH solution are needed to neutralize 35.0 mL of M H 2 SO 4 solution. First write a balanced Equation. ____NaOH + ____H 2 SO 4  ____H 2 O + ____Na 2 SO

21 Solution Stoichiometry: Determine how many mL of M NaOH solution is needed to neutralize 35.0 mL of M H 2 SO 4 solution. Now, let’s get organized. Place numerical Information and accompanying UNITS below each compound. ____NaOH + ____H 2 SO 4  ____H 2 O + ____Na 2 SO M ? mL 35.0 mL Since 1 L = 1000 mL, we can use this to save on the number of conversions Our Goal

22 Determine how many mL of M NaOH solution is needed to neutralize 35.0 mL of M H 2 SO 4 solution. Now let’s get to work converting. ____NaOH + ____H 2 SO 4  ____H 2 O + ____Na 2 SO M ? mL 35.0 mL = mL NaOH H 2 SO mL H 2 SO mol 1000 mL H 2 SO 4 NaOH 2 mol 1 mol H 2 SO mL NaOH mol NaOH 85.8 Units Match Solution Stoichiometry: shortcut

23 What volume of 0.40 M HCl solution is needed to completely neutralize 47.1 mL of 0.75 M Ba(OH) 2 ? 1st write out a balanced chemical equation Solution Stoichiometry

24 What volume of 0.40 M HCl solution is needed to completely neutralize 47.1 mL of 0.75 M Ba(OH) 2 ? 2HCl(aq) + Ba(OH) 2 (aq)  2H 2 O(l) + BaCl M 47.1 mL 0.75 M ? mL = mL HCl Ba(OH) mL 1 mol Ba(OH) 2 HCl 2 mol 0.40 mol HCl HCl 1000 mL 176 Units match Solution Stoichiometry

25 Solution Stochiometry Problem: A chemist performed a titration to standardize a barium hydroxide solution. If it took mL of M hydrochloric acid to neutralize mL of the barium hydroxide solution, what was the concentration of the barium hydroxide solution in moles per liter (M)? First write a balanced chemical reaction. ____HCl(aq) + ____Ba(OH) 2 (aq)  ____H 2 O(l) + ____BaCl 2 (aq) mL mol L mL ? mol L

26 Solution Stochiometry Problem: A chemist performed a titration to standardize a barium hydroxide solution. If it took mL of M hydrochloric acid to neutralize mL of the barium hydroxide solution, what was the concentration of the barium hydroxide solution in moles per liter (M)? ____HCl(aq) + ____Ba(OH) 2 (aq)  ____H 2 O(l) + ____BaCl 2 (aq) mL mol L mL ? mol L = mol Ba(OH) 2 L Ba(OH) x L Ba(OH) 2 Units Already Match on Bottom! Units match on top!

mL of Ca(OH) 2 solution was titrated with 19.2 mL of M HNO 3. Determine the molarity of the Ca(OH) 2 solution. We must first write a balanced equation. Solution Stochiometry Problem:

mL of Ca(OH) 2 solution was titrated with 19.2 mL of M HNO 3. Determine the molarity of the Ca(OH) 2 solution. Ca(OH) 2 (aq) + HNO 3 (aq)  H 2 O(l) + Ca(NO 3 ) 2 (aq) mL19.2 mL M = mol (Ca(OH) 2) L (Ca(OH) 2 ) 19.2 mL HNO x L ? M units match! Solution Stochiometry Problem:

29 Limiting/Excess/ Reactant and Theoretical Yield Problems : Potassium superoxide, KO 2, is used in rebreathing gas masks to generate oxygen. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) a. How many moles of O 2 can be produced from 0.15 mol KO 2 and 0.10 mol H 2 O? b. Determine the limiting reactant. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) First copy down the the BALANCED equation! Now place numerical the information below the compounds.

30 Limiting/Excess/ Reactant and Theoretical Yield Problems : Potassium superoxide, KO 2, is used in rebreathing gas masks to generate oxygen. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) a. How many moles of O 2 can be produced from 0.15 mol KO 2 and 0.10 mol H 2 O? b. Determine the limiting reactant. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) 0.15 mol 0.10 mol ? moles Two starting amounts? Where do we start? Hide one

31 Limiting/Excess/ Reactant and Theoretical Yield Problems : Potassium superoxide, KO 2, is used in rebreathing gas masks to generate oxygen. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) a. How many moles of O 2 can be produced from 0.15 mol KO 2 and 0.10 mol H 2 O? b. Determine the limiting reactant. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) 0.15 mol 0.10 mol ? moles Hide Based on: KO 2 = mol O mol KO

32 Potassium superoxide, KO 2, is used in rebreathing gas masks to generate oxygen. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) a. How many moles of O 2 can be produced from 0.15 mol KO 2 and 0.10 mol H 2 O? b. Determine the limiting reactant. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) 0.15 mol 0.10 mol ? moles Based on: KO 2 = mol O mol KO Hide Based on: H 2 O = mol O mol H2OH2O Limiting/Excess/ Reactant and Theoretical Yield Problems :

33 Limiting/Excess/ Reactant and Theoretical Yield Problems : Potassium superoxide, KO 2, is used in rebreathing gas masks to generate oxygen. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) a. How many moles of O 2 can be produced from 0.15 mol KO 2 and 0.10 mol H 2 O? Determine the limiting reactant. 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) 0.15 mol 0.10 mol ? moles Based on: KO 2 = mol O mol KO Based on: H 2 O = mol O mol H 2 O What is the theoretical yield? Hint: Which is the smallest amount? The is based upon the limiting reactant? It was limited by the amount of KO 2. H 2 O = excess (XS) reactant!

34 Theoretical yield vs. Actual yield Suppose the theoretical yield for an experiment was calculated to be 19.5 grams, and the experiment was performed, but only 12.3 grams of product were recovered. Determine the % yield. Theoretical yield = 19.5 g based on limiting reactant Actual yield = 12.3 g experimentally recovered

35 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) If a reaction vessel contains g of KO 2 and 47.0 g of H 2 O, how many grams of O 2 can be produced? 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) g47.0 g ? g Hide one Based on: KO 2 = g O g KO Limiting/Excess Reactant Problem with % Yield

36 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) If a reaction vessel contains g of KO 2 and 47.0 g of H 2 O, how many grams of O 2 can be produced? 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) g47.0 g ? g Based on: KO 2 = g O g KO Based on: H 2 O = g O 2 Question if only 35.2 g of O 2 were recovered, what was the percent yield? Hide 47.0 g H 2 O Limiting/Excess Reactant Problem with % Yield

37 If a reaction vessel contains g of KO 2 and 47.0 g of H 2 O, how many grams of O 2 can be produced? 4KO 2 (s) + 2H 2 O(l)  4KOH(s) + 3O 2 (g) g47.0 g ? g Based on: KO 2 = g O g KO Based on: H 2 O = g O g H 2 O Determine how many grams of Water were left over. The Difference between the above amounts is directly RELATED to the XS H 2 O = g of O 2 that could have been formed from the XS water. = g XS H 2 O g O

38 Calculate the molarity of a solution prepared by dissolving 25.6 grams of Al(NO 3 ) 3 in 455 mL of solution. After you have worked the problem, click here to see setup answer Try this problem (then check your answer):

39 Chemistry: Stoichiometry Unifying Theme: Constancy, Change, and Measurement WhyWhatHow Enduring Understandings Essential QuestionsMajor Indicators, PrioritizedAssessment Examples  The mole is basic unit of measurement in chemistry contains 6.02 x particles.  The mole is the bridge between microscopic and macroscopic world and is used in unit analysis.  Stoichiometry is used to predict quantities in chemical reactions.  Products are limited by the amount of reactants such as natural resources and the limitation can be predicted.  Mass of 1 mole substance can be determined based on the atomic mass in the Periodic Table.  How is the mole used in chemical calculations?  How is quantity of materials predicted in a chemical reaction?  How do available materials limit the amount of products?  How is molar mass calculated Essential  HS use the coefficients of a balanced equation to predict amounts of reactants and products.  HS4.4.5 demonstrate that adjusting quantities of reactants will affect the amounts of products formed.  HS4.4.A.A identify and define Avogadro’s number and the mole concept operationally and conceptually.  HS4.4.A.B utilize dimensional analysis to perform mole to mole, mass to mass, particle to mole, and mole to particle calculations.  HS4.4.A.D use formula mass to calculate percent composition of a compound.  HS.4.4A.F solve problems involving quantitative relationships in equations including stoichiometric concepts of mole to mole, particle to particle, mass to mass, mole to volume and volume to mole.  HS4.4.A.G manipulate the limiting reagent concept qualitatively to conclude that the starting materials of the chemical industry such as petroleum, are limited resources and decisions must be made about their wise consumption.  HS1.6.4 manipulate quantities and/or numerical values in algebraic equations.  HS1.7.4 recognize mathematics as an integral part of the scientific process.  HS calculate the molecular weight of a compound given in the Periodic Table. Pre-assessment -Brainstorm the collective terms such as dozen, pairs, gross, etc, and conversions between the terms and their numerical values. Formative Assessment -Develop a creative concept map to illustrate the relationships among mole, mass, volume and number of particles. Summative Assessment -Competition: Students are given a specific amount of iron filing and copper sulfate. They are required to return exact one gram of elemental copper after the reaction is completed. -Write an article for your school paper about the air pollution in your community. Be sure to include the stoichiometric analysis.

40 Chemistry: Stoichiometry How Suggested Instructional Sequence Differentiation Examples  Introduction of mole concept. - What is mole? - Determine the number of rice grains in a given container.  Guided practice in calculation of atomic mass, molar mass, and formula mass.  Utilize dimensional analysis to convert among mole, gram, volume and number of particles. - Lab Galvanized Iron: determine number of atoms of Zn coated on a piece of galvanized iron. - Guided practice: mole conversions using mole concept map.  Percent of composition; - Lab percent of water in popcorn - Lab determining an Empirical formula – such as copper sulfate hydrates.  Introduction of Stoichiometry - Demonstration: electrolysis of water to illustrate the mole ratio. - Lab Use stoichiometric relationship to analyze the amount of silver replaced from silver nitric solution with the copper.  Introduction of limiting reagent - Using manipulation to demonstrate limiting reagents (cake recipe) - A research project about the limitation of a natural resource, such as petroleum, copper.  Challenge -Design a lab to synthesize a quantitative product when given a variety of reactants -Design a lab to determine the empirical formula for a given hydrate compound.  Adjust Predict the volume of carbon dioxide that would be produced by adding specified amounts of vinegar to various teaspoons of baking soda. Carry out the activity and compare the experimental results with your prediction. Account for any differences in volume.  ESOL Create a PowerPoint presentation to explain stoichiometry