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1 [A how-to-guide on determining relative concentrations of reactants and products in chemical reactions] This packet belongs to: 1

2 Unit Description: In this project, you will learn how about basic solutions, which are mixtures made by mixing and dissolving one thing (solute) into another (solvent). You will also use your knowledge of chemical reactions and stoichiometry to predict how much product you will be making from a set of materials. In other words, you will be given a set of chemicals and will be asked to mix them together in order to create a chemical reaction. You will then use stoichiometry, which is the math behind the chemical reaction, to figure out how much material you will produce from a chemical reaction. Topics we will be studying: Conservation of matter/how to balance chemical reactions Dimensional analysis (review) Moles Concentration of solutions Solubility of solids, liquids and gases Stoichiometry Essential Questions: What happens when chemicals react? Is matter really conserved in chemical reactions? What factors affect how soluble solids, liquids and gases are? How can we use stoichiometry to calculate the amount of chemicals we start off with or end up with? What real-life applications can we use stoichiometry for? Products: Lab Report Test 2

3 Lesson 1: Chemical Quantities Introduction to Moles We live in a quantitative world meaning, we deal with numbers on a daily basis. For example, you get graded based on numbers, you buy objects using dollar amounts and you talk to your friends about the number of times you ve heard a song on the radio. You re constantly answering questions like how many? or how much? Scientists try to answer the same types of questions i.e., how many grams, atoms or molecules of hydrogen and nitrogen are needed to make fertilizer? Or how much baking soda and vinegar is needed to make 50 grams of sodium acetate? (You ll be doing a lab similar to that at the end of this unit). In these next couple of lessons, you will learn how to use various units to measure matter. You ve already learned how to describe the mass and the volume of objects using grams and liters and have used counting to describe the quantity of materials. Some units are used for indicating a specific number of items. For example, a pair of shoes is 2 shoes or a dozen apples is equal to 12 apples. These units are appropriate for counting objects as big as apples. However, what if you wanted to measure the amount of sand grains in a sand sculpture or the amount of atoms or molecules in a substance? The units that we use on a daily basis (like a pair or a dozen) are not appropriate for tiny, tiny particles that we can hardly see. Therefore, scientists came up with a new counting unit called the MOLE 1. 1 MOLE (mol) = particles, molecules, atoms, objects, things, etc. ( ) *Amadeo Avogadro di Quaregna ( ) was an Italian physics professor who helped clarify the difference between atoms and molecules. Converting From Moles to Particles EX: How many gummy bears are 2 mols of gummy bears? 1 Adapted from Prentice Hall: Chemistry p

4 EX: How many M&Ms are 5 mols of M&Ms? EX: How many molecules is 2.12 moles of C 3 H 8 (propane)? Converting From Particles to Moles EX: There are approximately 2.43 x molecules of water in the Pacific Ocean. How many moles of water is this? EX: The average American drinks 6,000 sodas a year. How many moles of soda is this? EX: How many moles of magnesium is 3.01 x atoms of magnesium? 4

5 Converting Between Moles and Grams In stores, apples are measured in three different ways. At a fruit stand, they are often sold by the count (3 for $2.40). In a supermarket, you usually buy apples by weight ($1.29/pound) or mass ($2.79/kg). At an orchard, you can buy apples by volume ($12.00/bushel). Each of these different ways to measure apples can be equated to a dozen apples: By count: 1 dozen apples = 12 apples For average-sized apples the following approximations can be used: By mass: 1 dozen apples = 2.0 kg apples By volume: 1 dozen apples = 0.2 bushels apples Knowing how the count, mass and volume of apples relate to a dozen apples allowed you to convert among these units. Using those conversion factors above and dimensional analysis, you could calculate the mass of a bushel of apples or the mass of 90-average sized apples. Likewise, in chemistry, you can convert between quantities or amounts of things and mass. Also, in a lab, it is too difficult to count out 6.02 x particles of a substance every time you want to measure out a mole of something. Instead, you can quickly figure out a mole of a substance by finding its molar mass (or how much 1 mole of a substance weighs). To do this, you will use the Periodic Table 2. 1 MOLE (mol) = Molar Mass = 2 Adapted from Prentice Hall: Chemistry p.288 5

6 Finding the Molar Mass of Elements & Compounds 1.) C 2.) Cu 3.) CO 2 4.) Cu 2 CO 3 (OH) 2 Converting Moles to Grams 1.) How many grams are 2 moles of oxygen (O 2 )? 2.) How many grams are 3.5 moles of water? 3.) How many grams is 2.4 moles of vinegar (CH 3 COOH)? 4.) How many grams is 0.6 moles of salt (NaCl)? 6

7 Converting Grams to Moles 1.) How many moles are in 28 grams of CO 2? 2.) Find the number of moles of argon in 452 g of argon. 3.) Find the grams in 1.26 x 10-4 mol of HC 2 H 3 O 2. 7

8 Practice with Converting Between Moles and Grams In this short activity, you will practice converting grams to moles, and grams to moles to particles. You will 1.) weigh each substance in grams 2.) find the molar mass 3.) convert grams to moles 4.) and if needed, convert moles to particles. Please show your work! Substance Mass (in grams) Molar Mass; 1 mole =? grams How many moles of substance do you have? CHALLENGE: how many particles do you have? Sugar C 12 H 22 O 11 Vinegar CH 3 COOH Water H 2 O Baking Soda NaHCO 3 8

9 Lesson 1: Homework Practice with Converting Between Moles, Particles and Grams Mole-Particle Conversions 1. How many moles of magnesium is 3.01 x atoms of magnesium? 2. How many molecules are there in 4.00 moles of glucose, C 6 H 12 O 6? 3. How many moles are 1.20 x atoms of phosphorous? 9

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11 Practice with Molar Mass Do the following practice problems below. Find the molar mass (what 1 mole of substance equals in grams) of each of the following substances: 1.) Nitrogen atoms, N 2.) Sodium chloride (table salt), NaCl 3.) Chalcopyrite (a copper-containing mineral), CuFeS 2 4.) Magnesium phosphate, Mg 3 (PO 4 ) 2 5.) Alunite (an aluminum mineral), KAl 3 (SO 4 ) 2 (OH) 6 (HINT: Verify that this formula includes 14 oxygen atoms) 11

12 Practice with Converting Between Moles and Grams 12

13 Lesson 2: Warmup 1) Define mole. 2) How many moles are present in 34 grams of Cu(OH) 2? 3) How many moles are present in 2.45 x molecules of CH 4? 4) How many grams are there in 3.4 x molecules of NH 3? 5) How are the terms molar mass and atomic mass different from one another? 13

14 Lesson 2: Chemical Quantities - Converting Between Moles and Liters; Mixed Mole Problems Yesterday, you learned how to convert between moles, particles and mass. Today, you will learn how to convert between moles and volume (liters). This conversion however ONLY WORKS FOR GASES! Here s why: Avogadro s hypothesis: Reason for this is. 1 MOLE (mol) = liters = particles What this means is. ***NOTE: This conversion only applies to gases at standard temperature and pressure (STP) which is Why? 14

15 Moles to Volume Conversion 1.) Determine the volume, in liters, of 0.60 mol of SO 2 gas at STP. 2.) What is the volume of 3.20 x 10-3 moles of CO 2 at STP. 3.) At STP, what volume does moles of C 2 H 6 occupy or take up? Volume to Moles Conversion 1.) How many moles does 44.8 L of Hydrogen gas at STP represent? 2.) A sample of oxygen gas occupies 6.2 L at STP. How many moles does that represent? 3.) How many moles of neon would occupy 450 ml at STP? (1000 ml = 1 L) 15

16 Practice Converting Between Moles and Liters for Gases In this activity, you will figure out how many moles and particles of gases you can fit in each of these containers. Container Volume (in L) How many moles of gas can fit in this? How many particles of gas can fit in this? 16

17 Mixed Mole Problems (The Mole Road Map) Now that you ve learned how to convert moles to particles, mass and volume of gases at STP, you can now convert between all these different quantities. To do so, you must use the mole as the in between step. See the mole road map below as a summary of these relationships: 17

18 Mixed Mole Problems Given unit Moles Desired unit 1. How many oxygen molecules are in 3.36 L of oxygen gas at STP? 2. Find the mass in grams of 2.00 x molecules of F 2? 3. Determine the volume in liters occupied by 14 g of nitrogen gas (N 2 ) at STP. 4. Find the mass, in grams, of 1.00 x molecules of N How many particles are there in 1.43 g of a molecular compound with a gram molecular mass of 233 g? 18

19 Lesson 2: Homework Converting Between Moles and Liters; Mixed Mole Problems Complete the following problems below: 19

20 Mole-Volume Conversions 1. Determine the volume, in liters, occupied by moles of a gas at STP. 2. How many moles of argon atoms are present in 11.2 L of argon gas at STP? 3. What is the volume of 0.05 mol of neon gas at STP? 4. What is the volume of 1.2 moles of water vapor at STP? 20

21 Mixed Mole Problems (Use the Mole Road Map!) 4. Aspartame is an artificial sweetener that is 160 times sweeter than sucrose (table sugar) when dissolved in water. It is marketed by G.D. Searle as Nutra Sweet. The molecular formula of aspartame is C 14 H 18 N 2 O 5. a) Calculate the gram-formula-mass (molar mass) of aspartame. b) How many moles of molecules are in 10 g of aspartame? c) What is the mass in grams of 1.56 moles of aspartame? d) How many molecules are in 5 mg of aspartame? Convert to grams first! 21

22 Lesson 3: Warmup Using your knowledge of mole calculations and unit conversions, determine how many moles and molecules there are in 1 gallon of gasoline. Assume that the molecular formula for gasoline (a liquid) is C 6 H 14 and that the density of gasoline is approximately 0.85 grams/ml. Other conversion factors you might need: 1 gallon = 3.79 liters. HINT: You will have to use the density of gasoline to convert to grams notice though, what units the density is. After putting gasoline in your car engine, it becomes carbon dioxide gas and water molecules. How many moles and liters of carbon dioxide do you get from 1 gallon of gasoline at STP? Conversion factors you need: 1 mole of gasoline = 6 moles of carbon dioxide. HINT: Take part of your answer from the first question (the one in moles) and convert it to liters of gas. 22

23 Lesson 3: Chemical Quantities - Solutions & Concentrations Part 1: What is a Solution? Definition: A solution is a. There are 2 parts: 1.) SOLVENT: 2.) SOLUTE For the following examples, identify which substance is the solvent and which is/are the solute(s). 1.) A gaseous solution (air) SOLVENT: SOLUTE(S): 2.) Gas-liquid solution (soda) made of water, carbonation (carbon dioxide), sweeteners, other flavors SOLVENT: SOLUTE(S): 23

24 3.) Solid-liquid solution (lemonade) SOLVENT: SOLUTE(S): 4.) Solid-solid solution (brass) common brass is made of 63% copper, 37% zinc SOLVENT: SOLUTE(S): 24

25 Measuring Concentrations of Solutions Yesterday, we learned that a solution is composed of a solvent (does the dissolving) and solute(s) (substances that are dissolved). We know that different solutions have different amounts of solutes and solvents in them. So how do we measure how much solute is in a solvent (called the concentration) of a solution? To measure the concentration of a solution, you simply compare the amount of solute to the amount of solvent. There are many ways of measuring concentration: 1.) grams of solute/liters of solution 2.) how many parts of solute per million parts of solution 3.) percentage (%) of solute to solution 4.) molarity (moles of solute/liters of solution) ***In this class, we will only use the two ways that are in bold print. Concentration Calculations Method #1: Grams/Liters 1.) Find the grams of solute 2.) Find the liters of solution 3.) Divide the grams of solute by the liters of solution FORMULA FOR CONCENTRATION (g/l): EX #1: 0.5 grams of sodium chloride is dissolved in water to make 0.05 liters of solution. Find the concentration of the solution in g/l. EX #2: 15 grams of Kool-Aid powder is dissolved in water to make 2.5 liters of Kool-Aid. Find the concentration of this solution in g/l. 25

26 Concentration Calculations Method #2: Moles/Liters Molarity = Moles/Liters, units are M or mol/l 1.) Find the moles of solute 2.) Find the liters of solution 3.) Divide the moles of solute by the liters of solution 4.) Put M on the end for units FORMULA FOR CONCENTRATION (M): EX #1: 0.5 moles of sodium chloride is dissolved to make 0.05 liters of solution. What is the concentration of this solution/the molarity (M)? EX #2: How many moles of calcium chloride would you need to make 450 ml of a 0.25 M solution? EX #3: What is the concentration in mol/liters (M) of a solution in which 0.45 grams of sodium nitrate (NaNO 3 ) are dissolved in 265 ml of solution? EX #4: How many grams of beryllium chloride (BeCl 2 ) would you need to add to 125 ml of water to make a M solution? 26

27 Practice with Concentration of Solutions Which concentration of juice tastes the best? You are now going to try 4 different concentrations of juice to figure out which one tastes the best! Trial # 1 Grams of juice powder (solute) Liters of solution Concentration (g/l) Molarity (concentration in mols/l or M) Which concentration was the best-tasting? 27

28 Lesson 3: Homework Solutions and Concentrations Calculate the concentrations (in g/l) for the following solutions: 1.) What is the concentration of a solution made when you dilute 35 grams of sodium carbonate to a volume of 3,400 ml? 2.) 0.5 grams of sodium chloride is dissolved to make 0.05 ml of solution. 3.) 734 grams of lithium sulfate are dissolved to make 2500 ml of solution. 4.) 6.7 x 10-2 grams of Pb(C 2 H 3 O 2 ) 4 are dissolved to make 3.5 ml of solution. Calculate the molarity (mol/l) of each of the following solutions: 5.) Suppose we had 1.00 mole of sucrose (it's about grams) and proceeded to mix it into some water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure that when everything was well-mixed, there was exactly 1.00 liter of solution. What would be the molarity of this solution? 6.) Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution. What's the molarity? 28

29 7.) What is the molarity when 0.75 mol is dissolved in 2.50 L of solution? 8.) grams of sucrose (C 12 H 22 O 11 ) is dissolved in 1.50 L of solution. What is the molarity? (HINT: first change grams to moles!) 9.) 49.8 grams of Potassium Iodide (KI) is dissolved in enough water to make 1.00 L of solution. What is the molarity? 10.) Calcuate the molarity when 75.0 grams of MgCl 2 is dissolved in ml of solution. 29

30 Lesson 4: Warmup Answer the following questions: 1.) What is the molarity (M) of sulfuric acid in a solution made by adding 3.4 grams of sulfuric acid (H 2 SO 4 ) to 3,500 ml of water? 2.) Explain how to make at least one liter of a 1.25 M ammonium hydroxide (NH 4 OH) solution i.e. how many moles and how many grams of NH 4 OH do we need for 1 liter of solution? 3.) How many grams of ammonia (NH 3 ) are present in 5.0 L of a M solution? 30

31 Lesson 4: Chemical Reactions Conservation of Matter Review- How many molecules and elements do I have? Formulas How many molecules (units) are there? Elements/# of atoms per element 1. ) Fe 2 (SO 4 ) 3 2.) 3 CH 4 3.) 3 H 2 (SO 4 ) The following chemical reaction is photosynthesis, or the process by which plants make food (sugars). Fill out the table below based on this chemical reaction. Reactants How many molecules (units) are there? Elements/# of atoms per element Products 31

32 Discover Activity with coins 1.) Sort stacks into pennies, nickels, dimes and quarters. Fill out the table below. coins Pennies Nickels Dimes Quarters TOTAL $ amount 2.) Now mix them together and make 3 random stacks of these coins. Fill out the table below. coins Pennies Nickels Dimes Quarters TOTAL $ amount 3.) Mix the coins together again and now stack them into 4 random stacks. coins Pennies Nickels Dimes Quarters TOTAL $ amount Described what happened in this activity. Did the number of pennies, nickels, dimes and quarters change? Did the total amount of money change? Why or why not? Conservation of Mass What did you notice happening in this picture and with this chemical reaction? The principle of conservation of mass states that in a chemical reaction. Balancing Chemical Equations Because of the principle of conservation of mass, there must be.. **THEREFORE, a chemical equation MUST be. 32

33 STEPS TO BALANCING CHEMICAL EQUATIONS 1.) Write the equation 2.) Count the atoms 3.) Use the coefficients (numbers in front) to balance the atoms 4.) Look back and check Practice 1.) 2.) 33

34 3.) 4.) Methane gas (CH 4 ) reacts with chlorine gas (Cl 2 ) to form chloroform (CHCl 3 ) and hydrochloric acid (HCl). Balance this equation. 5.) Balance the following equation: Fe + H 2 (SO 4 ) > Fe 2 (SO 4 ) 3 + H 2 34

35 Lesson 4: Homework Conservation of Matter For each problem, balance the chemical equation if needed. If the equation is already balanced, you can just write equation already balanced. ***Hint: Substitute (NO 3 ) with X 35

36 If you want to check your answers or need help on # 7 check out this video: 6.) Al + O > Al 2 O 3 7.) C 2 H 4 + O > CO 2 + H 2 O 8.) C 2 H 4 + O > CO 2 + H 2 O 9.) C 2 H 6 + O > CO 2 + H 2 O 10.) Fe 2 O 3 + H 2 SO > Fe 2 (SO 4 ) 3 + H 2 O ***HINT: SUBSTITUTE SO 4 for X and do the problem. Then plug SO 4 back in for X. 36

37 Lesson 5: Warmup Balance the following chemical equations: 1) N 2 + H 2 NH 3 2) KClO 3 KCl + O 2 3) NaCl + F 2 NaF + Cl 2 4) H 2 + O 2 H 2 O 5) Pb(OH) 2 + HCl H 2 O + PbCl 2 6) AlBr 3 + K 2 SO 4 KBr + Al 2 (SO 4 ) 3 7) CH 4 + O 2 CO 2 + H 2 O 8) C 3 H 8 + O 2 CO 2 + H 2 O 9) FeCl 3 + NaOH Fe(OH) 3 + NaCl 10) C 8 H 18 + O 2 CO 2 + H 2 O (CHALLENGE!!) 37

38 Lesson 5: Stoichiometry Part 1 Silk is one of the most beautiful and luxurious of all fabrics. It is spun from the cocoons of silkworms. Silk manufacturers know from experience that to produce enough silk to make just one elegant Japanese kimono they will need over 3000 cocoons. In a similar fashion, when you bake cookies, you probably use a recipe. A cookie recipe tells you the precise amount of ingredients to mix to make a certain number of cookies. If you need a larger amount of cookies, you can double or triple the amounts of ingredients. In chemistry, scientists need to know how much reactant is needed to make a certain amount of product. The answer lies in the chemical equation which is like the recipe for baking cookies. From a balanced chemical equation, you can determine the quantities of reactants and products in a reaction. 3 We will use stoichiometry, which is the study of the relationship between materials in a chemical equation, to help us figure out the amounts of materials we need or the amount we will receive in a chemical reaction. For example, below is a chemical reaction or recipe that I use to make sandwiches 4 breads + 2 cheese + 2 tomato + 6 pickles ---> 2 sandwiches Answer the following questions: 1.) If I want to make 11 sandwiches, how many pickles do I need? Conversion unit: Solve: 2.) If I want to make 3 sandwiches, how many pieces of bread do I need? Conversion unit: 3 Adapted from Prentice Hall: Chemistry p

39 Solve: 3.) If I have 30 tomatoes, how many sandwiches can I make? Conversion unit: Solve: 4.) If I have 9 pieces of bread, how many sandwiches can I make? Conversion unit: Solve: 39

40 Example #1: Now, try with a real chemical reaction. EX: Hydrogen reacts with oxygen to give us water. H 2 (g) + O 2 (g) > H 2 O(l) molecule/moles molecule/moles molecule/moles 1.) First, ALWAYS make sure the equation is balanced. If it isn t, please balance it. (Otherwise, the rest of your answers will be incorrect. 2.) In this reaction, if I have 1 molecule of O 2, how many molecules of H 2 do I have? How many molecules of water (H 2 O) do I have? 3.) In this reaction, if I have 4 moles of H 2, how many moles of O 2 do I have? How many moles of water (H 2 O) do I have? Show your work: 4.) If I want to make 6.5 moles of H 2 O, how many moles of H 2 do I need? How many moles of O 2 do I need? 40

41 5.) Oftentimes in a lab setting, you will have to convert from moles to grams because the only way to measure out moles is to weigh them with a balance. Using the chemical equation or recipe, I want you to convert the moles into grams (find the molar mass). 1 mol of H 2 = 1 mol of O 2 = 1 mol of H 2 O = 6.) If I want to form 200 grams of H 2 O, how many moles of H 2 do I need? How many grams of H 2 is that? 7.) If I want to form 200 grams of H 2 O, how many moles of O 2 do I need? How many grams of O 2 is that? 41

42 Example #2 The chemical reaction for producing pure copper (refining copper) is below. CuO = copper oxide 2 CuO (s) + C(s) -----> 2 Cu(s) + CO 2 (g) molecules/moles molecules/moles molecules/moles molecules/moles 1.) Is this reaction balanced? How do you know? 2.) Write down the amount of moles you see for each reactant and product under the equation. 3.) A refiner needs to convert g of CuO to pure Cu. What mass of C is needed for this reaction? ***Remember, you need to convert to moles in order to use the chemical equation or the recipe! 42

43 Lesson 5: Homework- Practice with Stoichioimetry Part 1 MOLAR RELATIONSHIPS Complete the problems below. Base your answers to the following questions on this equation. CuO(s) + 2 HCl(aq) -----> CuCl 2 (aq) + H 2 O(l) 1.) Is this equation balanced? How do you know? If it is not balanced, please do so. 2.) Find the molar mass of each reactant and product in the equation: a.) 1 mole of CuO = g b.) 1 mole of HCl = g c.) 1 mole of CuCl 2 = g d.) 1 mole of H 2 O = g 3.) Find the mass (in grams) of each of the following substances: a.) 2.0 mol HCl = g b.) 5.0 mol HCl = g 43

44 c.) 0.50 mol of CuO = g 4.) Find the number of moles of substance that are represented by: a.) g of CuCl 2 = moles b.) g of CuCl 2 = moles c.) 73.0 g of HCl = moles 5.) a.) How many moles of CuO are needed to react with 4 mol of HCl? (HINT: Use the chemical equation!) b.) How many moles of HCl are needed to react with 4 mol of CuO? (HINT: Use the chemical equation!) 6.) a.) If I have 200 grams of CuO, how many moles and grams of H 2 O will I produce according to this chemical equation? b.) If I ended up making 300 grams of CuCl 2, how many moles and grams of HCl did I have to start off with according to the chemical equation? 44

45 Lesson 6: Warmup Practice with Real-Life Stoichiometry I found this really cool recipe at to make Cake Batter White Chocolate Fudge. I want to make enough squares to feed the class. Here is the recipe that I found below. It makes 18 bars and I need to increase the amounts to make more. Help me figure out how much of each ingredient I need to be able to make the exact amount of bars for the students in our class. Recipe for Cake Batter White Chocolate Fudge: INGREDIENTS 1 cup of Betty Crocker Supermoist white or yellow cake mix (or any brand white or yellow cake mix) 1 cup of powdered sugar 0.25 cups of salted butter, cut into 2 pieces cups of milk 0.33 cups of white chocolate chips 0.25 cups of rainbow sprinkles Makes 18 bars STEPS Spray 8 8 baking pan with nonstick spray. Set aside. Mix together cake mix and powdered sugar in a large bowl. Add milk and butter (do not stir them in) and microwave for 2 minutes. Once done, immediately begin mixing everything together. The batter will be very thick. Fold in white chocolate and sprinkles. Stir gently. You do not want the sprinkles to leak their color. Spoon into prepared baking pan, making sure it is level and smooth at the top. Chill in the refrigerator for at least 2 hours. Cut into squares and enjoy. *Store fudge in the refrigerator. 45

46 What amounts of ingredients do we need? 1.) First, write out an equation for this recipe below: 2.) Count how many students we have in class today. 3.) Use stoichiometry (and dimensional analysis/conversions) to figure out the new ingredients for the amount of students in our class. cup(s) of Betty Crocker Supermoist white or yellow cake mix (or any brand white or yellow cake mix) cups(s) of powdered sugar cups(s) of salted butter cups(s) of milk cups(s) of white chocolate chips cups(s) of rainbow sprinkles 46

47 Lesson 6: Practice with Stoichioimetry Part 2 For each problem, follow these steps: 1.) Balance the chemical equation 2.) convert to moles to use the recipe 3.) convert back to the units that you need 1.) Given the unbalanced decomposition reaction of baking soda: NaHCO 3 (s) + heat ===> Na 2 CO 3 (s) + CO 2 (g) + H 2 O (g) NaHCO 3 = baking soda/sodium bicarbonate Na 2 CO 3 = sodium carbonate a.) First, balance the chemical equation. Write the new, balanced equation down here: b.) How many grams of sodium carbonate (Na 2 CO 3 ) are produced by the decomposition of 42.0 grams of baking soda (NaHCO 3 )? (HINT: first convert to moles to use the recipe!) c.) What volumes of carbon dioxide and water are produced at STP? (HINT: first convert to moles to use the recipe!) 47

48 2.) The catalytic decomposition of hydrogen peroxide (H 2 O 2 ) is: a.) Balance the reaction. Write your new equation below: H 2 O 2 (aq) ===> H 2 O (l) + O 2 (g) b.) How many moles of water and oxygen are produced by the decomposition of 68.0 grams of hydrogen peroxide? c.) How many molecules (particles) of water are produced? d.) How many grams of oxygen are formed? 48

49 3.) If grams of potassium metal reacts with water, then how many grams of potassium hydroxide are formed? What volume of hydrogen gas, in liters, is formed at STP? Be sure to balance the reaction first. K (s) + H 2 O (l) KOH (aq) + H 2(g) a.) Balance the equation and write the new one below: b.) How many grams of potassium hydroxide (KOH) are formed if we use grams of potassium (K) metal reacts with water? c.) What volume of hydrogen gas, in liters, is formed at STP? 49

50 Lesson 6: Homework Practice with Stoichiometry Part 2 Solve the following problems. 1.) The burning of solid sulfur in air produces sulfur dioxide gas. S + O 2 SO 2 a.) Balance the reaction if needed. Write the new, balanced equation below. b.) How many moles and molecules (particles) of sulfur dioxide does the burning of 3 moles of sulfur form? c.) Calculate the volume of sulfur dioxide produced at STP. 50

51 2.) The Haber reaction produces ammonia, an important nitrogenous compound needed to make plant fertilizers. The unbalanced reaction is: N 2 (g) + H 2 (g) ===> NH 3 (g) + heat. a.) First, balance the chemical reaction. Write the new equation below: b.) If grams of ammonia (NH 3 ) are produced, then how many grams of nitrogen gas (N 2 ) are needed? c.) If grams of ammonia (NH 3 ) are produced, how many molecules of hydrogen gas (H 2 ) are needed? 51

52 3.) The unbalanced single displacement reaction between sodium metal and water is quite violent: Na (s) + H 2 O (l) ===> NaOH (aq) + H 2 (g) + heat + light a.) Balance the equation first. Write it down here: b.) If 44.8 liters of hydrogen gas are formed at STP, then how many grams of sodium are needed? c.) If 44.8 liters of hydrogen gas are formed at STP, then how many grams of water are needed? 52

53 Name: Date: Period: OVERVIEW Stoichiometry is the relation between the quantities of that take part in a reaction. In other words, we can use stoichiomety to figure out how much of a product we will produce knowing the amount of reactants we start with. You will be conducting a lab in which you mix sodium hydrogen carbonate, NaHCO 3, (baking soda) and acetic acid, CH 3 COOH, (vinegar) together and then you will observe the results. You will also predict the amount of carbon dioxide, water and sodium acetate (NaCH 3 COO) produced. You will then measure, in grams, how much sodium acetate (which is a whitish-clear powder used in concrete and food seasonings) you actually produced from the lab and will calculate the percent yield to see if the amount you got actually matches up with what you calculated. Please make sure you take good notes and observations because you will be writing a formal lab report on this lab. The following is the chemical reaction that will take place: NaHCO 3 (aq) + CH 3 COOH (aq) ----> CO 2 (g) + H 2 O (l) + NaCH 3 COO (aq) Baking soda + vinegar ----> carbon dioxide + water + sodium acetate INTRODUCTION In this lab, you will mix 0.05 moles of baking soda with an excess (a bunch) of vinegar. By doing this, you will (hopefully!) produce the amount of sodium acetate that you have predicted from your stoichiometric calculations. Baking Soda sodium hydrogen carbonate (NaHCO 3 ) Vinegar acetic acid (CH 3 COOH) For our reaction, you will use 0.05 moles of baking soda, which we will call by its chemical name, sodium hydrogen carbonate (NaHCO 3 ) for the rest of this lab. If we use much more than 0.05 moles of baking soda, the reaction will be too large and we will risk having some of the reaction products pour over the side of the flask when we mix it with the vinegar (which we call acetic acid CH 3 COOH). PRE-LAB QUESTIONS Use the information given in the Overview and Introduction sections to answer the following questions: 1.) What are the reactants of this reaction? 2.) What are the products of this reaction? 3.) Is the chemical equation balanced or not? Show your work. If it is not balanced, please balance it! 53

54 4.) What do you think the purpose of completing this lab is? Why do you think doing this lab might be useful for you as a student? Write your answers in complete sentences. 5.) You re told in the Introduction that you will be using 0.05 moles of baking soda. What is this measurement in grams? a.) First, find the molar mass of baking soda (sodium hydrogen carbonate NaHCO 3 ). Show your work below: b.) Next, convert 0.05 moles of sodium hydrogen carbonate to grams. Show your work below: FOR THIS LAB, WE WILL USE GRAMS OF SODIUM HYDROGEN CARBONATE (NaHCO 3 ) 6.) CONCENTRATION In the lab, we will be mixing the amount of sodium hydrogen carbonate (baking soda) that you calculated in #5 with 30 ml of water and 150 ml of vinegar. What will the concentration of this solution be? Show your work below: Grams of solute: g Moles of solute: moles (show how you got this answer below) Liters of solvent: L Concentration: M (show your work for how you got this answer) 54

55 7.) STOICHIOMETRY a.) Now, using stoichiometry, the equation on the previous page and the fact that we are starting off with 0.05 moles of sodium hydrogen carbonate (NaHCO 3 ), find how many moles and liters of CO 2 you expect to get. Show your calculations below: b.) How many moles and grams of H 2 O do you expect to get? Show your work below: c.) How many moles and grams of sodium acetate do you expect to get? Show your work below. Record this answer in your Data and Observations Section. 8.) PERCENT YIELD At the end of experiments, scientists calculate a percent yield based on the amount of product they actually make. A percent yield is a calculation that compares the theoretical yield (the predicted amount you re supposed to get) versus the actual yield (the amount you actually get). The formula for percent yield is: Getting a percent yield close to 100% (like 95% for example) is good because it means that you made almost as much as what you are supposed to make based on the equation. A percent yield around 50% for example is not so good and means that potentially something went wrong in the lab and you weren t able to produce as much product as you were supposed to. 55

56 Try these examples below: EX #1: If I produce 3.0 grams of sodium acetate, what is my percent yield? What would the actual amount of product be: Based on your answer in #6c, what is your theoretical yield of sodium acetate? Put it into the formula and find the percent yield. Show your work below: EX #2: If I produce 4.0 grams of sodium acetate, what is my percent yield? What would the actual amount of product be: Based on your answer in #6c, what is your theoretical yield of sodium acetate? Put it into the formula and find the percent yield. Show your work below: 9.) What might happen in a lab that would cause the percent yield to be lower than 100%? Discuss specific examples of how this might happen. 56

57 MATERIALS grams of baking soda (how much did you calculate you would need in #5 of the pre-lab questions?_ 150 ml of vinegar 1 cup A 500 ml flask Stirring rod 30 ml of water Hot plate Graduated cylinder METHODS In this section, you will now carry out the reaction that was discussed at the beginning of this lab. 1.) Observe 3 physical properties of vinegar and baking soda before mixing. Write down your observations in the Data & Observation section of this lab. 2.) In a cup, measure out the weight of sodium hydrogen carbonate that you calculated you would need in the introduction section of this lab. Don t forget to tare (zero) the weight of the cup. Make sure the amount that you use is as close as possible to the amount that you calculated. Write the exact amount of sodium hydrogen carbonate that you used here: Amount of sodium hydrogen carbonate that you actually used: gram. Record this mass in the Data and Observation Section. 3.) Add 30 ml of water to the cup containing the sodium hydrogen carbonate. Stir the solution until most or all of it is dissolved (if a little won t dissolve, that s okay). 4.) Weigh a 500 ml flask. You will need the weight of an empty flask at the end of the lab. Weight of empty 500 ml flask: grams. Record this mass in the Data and Observation Section. 5.) Add the sodium hydrogen carbonate solution to the empty 500 ml flask. 6.) In a graduated cylinder, measure out 150 ml of acetic acid (aka vinegar) and slowly add it to the sodium hydrogen carbonate solution. You will observe the formation of bubbles when the acetic acid is added to the sodium hydrogen carbonate solution. Wait until the bubbling subsides before adding more acetic acid. When all the acetic acid has been added, stir for two minutes before moving on to step 7. Record your observations of what happens when you mix the acetic acid and sodium hydrogen carbonate together in the Data and Observation Section. 57

58 7.) When the solution is calm again (there may be a few bubbles rising from the bottom of the flask this is normal), move the flask to a hot plate and heat it to boiling. Be careful that the flask does not boil over because this will cause errors in your calculations. Put the flask in the hood. 8.) When all of the liquid in the solution has boiled away, remove the flask from the hot plate. The powder that you observe inside is the product of the reaction, sodium acetate. Once the flask has had a few minutes to cool down to room temperature, measure and record its weight. Weight of the flask, after the water has evaporated:. Record this mass in the Data and Observation Section. Also, record what the leftover sodium acetate powder looks like in the same section. 9.) When done, rinse out the flask and any other glassware you used. All waste can go down the sink. 58

59 DATA AND OBSERVATIONS DATA TABLE Actual amount of sodium hydrogen carbonate (baking soda/nahco 3 ) used: Expected (calculated) amount of sodium acetate to be produced: Mass of empty 500-mL flask: Mass of 500-mL flask after water has evaporated: Actual mass of sodium acetate produced: Percent Yield of Sodium Acetate produced: OBSERVATION TABLE Three physical properties of sodium hydrogen carbonate (baking soda/nahco 3 ): Three physical properties of acetic acid (vinegar/ch 3 COOH): Observations of chemical reaction after mixing the baking soda and vinegar together: Observations of sodium acetate powder after water has evaporated: 59

60 CONCLUSION Answer the following questions: 1.) In this experiment, did a chemical reaction take place? How do you know? What evidence tells you whether a chemical reaction happened or not? 2.) Why do scientists use stoichioimetry? How did it help us in this lab? What did we figure out or calculate using stoichioimetry? 3.) Using the mass of the sodium acetate that you actually got and the mass of the sodium acetate that you predicted you would get, calculate the percent yield for this experiment. Show your calculations below. (If you ve forgotten how to do this, refer back to the pre-lab section #8). Actual mass of the sodium acetate that you produced: grams (show calculation below) Expected (theoretical) mass of the sodium acetate: grams Percent yield: % (show calculations below) 4.) Was your percent yield for sodium acetate 100%? Why or why not? 5.) Do you think it is common for scientists to get a 100% yield for chemical reactions and experiments? Why or why not? 60

61 6.) You measured how many grams you actually got for sodium acetate at the end of the chemical reaction. Using your knowledge of moles and particles and stoichiometry, figure out how many molecules (particles) of sodium acetate you actually ended up with. Show your calculations below. (HINT: start with the grams, go to moles and then particles). Actual mass of sodium acetate at the end of the lab: grams What is this in moles? moles. Show work below. (HINT: first find the molar mass) What is this in particles? molecules. Show work below. 61

62 An essential part of conducting experiments in chemistry is reporting your results and findings in a formal lab report. You will be writing a lab report to convey everything you did and learned from the chemical reaction of baking soda and vinegar. Use the following outline below. A google template has been shared with you to fill out!!! ALL lab reports must be completed INDIVIDUALLY!!! You and your group members may share DATA, but all answers, paragraphs and observations must be written in your OWN WORDS!!!!! Title Page You must have a title page that includes o o o o The title of the experiment (please do NOT call it stoichiometry lab report, be more specific about what chemical reaction/experiment we conducted). Please refer to the title section below. Your name and the names of any lab partners. Your instructor's name. The date the report is due. Introduction Things to include in your introduction: What chemical reaction did we perform in this lab? What materials did we react together? What were the reactants and products? Summarize how we did the baking soda and vinegar lab. (In a couple of sentences, explain what steps we took in this lab- remember this is a SHORT summary. You will write a much more detailed explanation in the procedure). What was the purpose of doing this lab? What is the purpose of stoichiometry? What did we calculate using stoichiometry in this lab? Type up and explain the calculation use used to find the amount of baking soda in grams to use for this lab (prelab question #5). Type up and explain the calculation we used to find the concentration of the solution we made from mixing baking soda, water and vinegar together (pre-lab question #6) Type up and explain the calculation we used to find the expected amount of sodium acetate we would get from this experiment (pre-lab question #7c). Materials List everything needed to complete your experiment. Be as specific as possible. Ex: 20 grams of baking soda (not just baking soda) Methods Describe the steps you completed during your investigation. This is your procedure. Be sufficiently detailed that anyone could read this section and duplicate your experiment. Write your method in paragraph form. You may use the instructions I gave you, but do NOT copy it word for word. You also need to write your methods section in first person use words like We. Data & Observations Type up the data table and the observation table. Conclusion Type up the answers to the conclusion questions and any calculations. 62

63 Reference Sheets Here are some notes that you might want to refer to throughout the unit: Converting between Moles, Particles, Grams and Volume of Gases at STP: STP = standard temperature and pressure (0 C = 273 K and 1 atm) **To find the molar mass, look up the atomic mass, in grams of each element on the periodic table Diagram taken from: 63

64 Calculating Concentrations Concentration Method #1: Grams/Liters 1.) Find the grams of solute 2.) Find the liters of solution 3.) Divide the grams of solute by the liters of solution Formula: Concentration (g/l) = grams of solute/liters of solution Concentration Method #2: Moles/Liter or M 1.) Find the moles of solute 2.) Find the liters of solution 3.) Divide the moles of solute by the liters of solution 4.) Put M on the end for units Formula: Concentration (mol/l) = moles of solute/liters of solution Balancing Equations 1.) Write the equation H 2 + O > H 2 O 2.) Count the atoms H 2 + O > H 2 O 2 H, 2 O 2 H, 1 O (oxygen is NOT balanced) 2(2H) 2 O 2(2 H, 1 O) 4 H 2 O 4 H, 2 O (so now everything is balanced) 3.) Use the coefficients (numbers in front) to balance the atoms 2 H O > 2 H 2 O 4.) Look back and check if everything is balanced 64

65 Stoichiometry How to go from moles of one reactant/product to the moles of another reactant/product 1.) First, make sure your chemical reaction is balanced. NaHCO 3 (s) + heat ===> Na 2 CO 3 (s) + CO 2 (g) + H 2 O (g) (NOT balanced) 2 NaHCO 3 (s) + heat ===> Na 2 CO 3 (s) + CO 2 (g) + H 2 O (g) (now it s BALANCED) 2.) Look to the chemical reaction to tell you the ingredients or how many moles of each substance you need. Look at the coefficients (number in front of each substance). According to the balanced equation above, you need 2 moles of NaHCO 3 to get 1 mole of Na 2 CO 3, 1 mole of CO 2 and 1 mole of H 2 O. 3.) Then turn these ingredients into conversion factors. 2 mol NaHCO 3 = 1 mol Na 2 CO 3 = 1 mol CO 2 = 1 mol H 2 O 4.) If you are going from any other unit (grams, liters, # of particles), you MUST USE MOLES first to go from one reactant/product to another reactant/product. USE the MOLE ROAD MAP also. EX: How many grams of sodium carbonate (Na 2 CO 3 ) are produced by the decomposition of 42.0 grams of baking soda (NaHCO 3 )? (HINT: first convert to moles to use the recipe!) 65

66 Answers Lesson 1: Practice with Converting Between Moles, Particles and Grams Mole-Particle Conversion 1.) 0.05 mol 3.) 19.9 mol I. A.) x molecules of water C.) 6.02 x molecules II. A.) 2 mol of water Practice with Molar Mass 1.) grams 3.) grams 5.) grams III A.) grams IV. A.) 3.96 moles C.) grams C.) 0.5 mol Lesson 2: Converting Between Moles and Liters; Mixed Mole Problems V. A.) 44.8 L C.) 336 L VI. A.) 2 mol C.) 1 mol Mole-Volume Conversions 1.) L 3.) 1.12 L Mixed-Mole Problems 4 a.) g c.) g Lesson 3: Solutions and Concentrations 1.) 10.3 g/l 3.) g/l 5.) I M 7.) 0.3 M 9.) 0.3 M 66

67 Lesson 4: Conversion of Matter 1a.) 2 C + O 2 ---> 2 CO 3.) 2 O 3 ---> 3 O 2 5.) Cu + 2 AgNO > Cu(NO 3 ) Ag 7.) C 2 H O 2 ---> 2 CO H 2 O 9.) 2 C 2 H O > 4 CO H 2 O Lesson 5: Practice with Stoichiometry Part 1 1.) balanced 2. a.) g c.) g 3. a.) 7.00 mol c.) 2.00 mol 4. a.) 2 mol 5. a.) 2 mol 6 a.) 2.51 mols of H 2 O = 45.3 grams of H 2 O Lesson 6: Practice with Stoichiometry Part 2 1.)a.) balanced! B.) 3 mol; x molecules c.) 67.2 L 3.) balanced equation is 2 Na + 2 H 2 O ----> 2 NaOH + H 2 b.) 0.25 mol c.) 3.01 x molecules 67

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