Chemistry Name: Problems and Questions Stoichiometry Hour: Answer the following questions using complete sentences when necessary. On numerical problems, show all work, circle your answers, and follow all rules of significant figures for full credit. 1. Demonstrate conservation of mass in each of the reactions below. a. The reactions of zinc and oxygen gas. b. The decomposition of potassium chlorate into potassium chloride and another product. c. The reaction of ammonia gas and nitrogen monoxide produces nitrogen gas and water. 2. Identify all the possible mole ratios in the reaction of magnesium oxide and iron (III) sulfate. 3. Solid aluminum reacts with copper (II) sulfate. a. How many moles of copper (II) sulfate will be needed to create 3.40 moles of aluminum sulfate if excess aluminum is available? b. How many moles of copper metal will be created from 2.30 moles of aluminum metal if copper (II) sulfate is in excess? 4. Carbon disulfide is an important industrial solvent. It is prepared by the reaction of coke (carbon in the form of charcoal and graphite) with sulfur dioxide: Carbon and sulfur dioxide yields carbon disulfide and carbon monoxide. a. How many moles of carbon are needed to react with excess sulfur dioxide to produce 34.5 moles of carbon disulfide? b. How many moles of carbon disulfide will be produced if 23.5 moles of sulfur dioxide react with excess carbon? 5. Aqueous solutions of aluminum hydroxide and hydrogen react. (Ignore the activity series) a. Write the balanced chemical reaction. b. How many moles of each reactant are needed to form 600. g of water? c. Calculate the number of grams of each reactant needed to produce 10.0 moles of aluminum. 6. Aqueous solutions of magnesium hydroxide and hydrogen phosphate (phosphoric acid) react. a. Calculate the mass needed of hydrogen phosphate to create 34.5 g of water. b. How many grams of magnesium phosphate will be created if 76.9 g of magnesium hydroxide is reacted with excess hydrogen phosphate? 7. Solid calcium carbonate and aqueous hydrogen phosphate (phosphoric acid) will yield aqueous calcium phosphate, gaseous carbon dioxide, and liquid water a. If 25.5 g of calcium carbonate reacts with excess hydrogen phosphate, how many grams of carbon dioxide will be produced? b. Calculate the number of grams of water that will be produced when 35.7 g of calcium carbonate is reacted with excess hydrogen phosphate? c. What mass of hydrogen phosphate will react with excess calcium carbonate to produce 45.9 g of calcium phosphate? 8. Solid lithium nitride reacts with water to form ammonia gas (NH 3) and aqueous lithium hydroxide at S.T.P. a. What mass of water is needed to react with 98.7 g of lithium nitride? b. When the above reaction takes place and 98.7 g of lithium nitride react, how many molecules of ammonia will be produced? c. Calculate the number of grams of lithium nitride that must be added to an excess of water to produce 45.0 L of ammonia. 9. Iron (III) oxide solid and gaseous carbon monoxide yield iron solid and carbon dioxide gas. a. How many grams of iron (III) oxide will be needed to produce 45.5 L of carbon dioxide gas (at S.T.P.)? b. How many molecules of carbon monoxide will be created if 45.5 L of carbon dioxide gas is produced (at S.T.P.)? c. If 4.56x10 23 molecules of iron (III) oxide react with excess carbon monoxide, how many grams of iron solid will be produced?
10. Oxygen gas and aqueous sodium hydroxide are produced by reacting water and solid sodium peroxide (Na 2O 2). a. Calculate the mass of sodium peroxide in grams needed to form 3.20 g of oxygen. b. How many grams of sodium hydroxide are produced when 3.20 g of oxygen is formed? c. When 0.480 g of sodium peroxide is dropped into excess water, how many liters of oxygen gas will be formed (at S.T.P.)? 11. Define what a limiting reactant is. How would you identify a limiting reagent in a chemical reaction? 12. Given the reactant amounts specified in each chemical equation, determine the limiting reactant in each case: a. HCl + NaOH NaCl + H 2O 2.00 mol 2.50 mol b. Zn + 2HCl ZnCl 2 + H 2 2.50 mol 6.00 mol c. 2Fe(OH) 3 + 3H 2SO 4 Fe 2(SO 4) 3 + 6H 2O 4.00 mol 6.50 mol 13. For each reaction in #12, determine the number of moles of excess reactant that remains. 14. Write and balance the combustion reaction of acetylene, C 2H 2. a. What will be the limiting reagent if 4.80 mol of acetylene reacts with 14.8 mol of oxygen gas? b. Using the balanced chemical reaction, and the limiting reagent's amount from letter (b), how many grams of water will be produced? 15. Aqueous solutions of sodium hydroxide and hydrogen sulfate react. a. If 20.0 grams of sodium hydroxide react with 30.0 grams of hydrogen sulfate to produce sodium sulfate, which reactant is the limiting reagent? Prove your answer with circled numerical answers. b. Using the limiting reagent's mass from (a), how many grams of water will be formed? 16. Copper metal is reacted with an aqueous solution of silver nitrate (copper will react as Cu +2 ). a. If 5.00 grams of copper metal reacts with a solution containing 20.0 grams of silver nitrate, prove then state which reactant is the limiting reagent. b. How many grams of silver metal will be formed given the amounts in (a)? 17. Calcium carbonate undergoes decomposition through the following reaction: CaCO 3(s) CaO (s) + CO 2(g) a. If 25.4 g of CaCO 3 react to produce 13.2 g of CaO, what is the percent yield of CaO? 18. When 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide, then 57.8 g of iron is produced along with an amount of carbon dioxide. What is the percent yield of the reaction? 19. When 50.0 g of silicon dioxide is heated with an excess of carbon, 32.2 g of silicon carbide is produced along with an amount of carbon monoxide. What is the percent yield of the reaction? 20. If 32.5 g silver acetate reacts with excess sodium phosphate to produce sodium acetate and 15.5 g of silver phosphate, what is the percent yield of the reaction? 21. If 5.00 g of potassium chlorate decomposes into potassium chloride and 1.50 g of oxygen gas, what is the percent yield of the reaction? 22. If 20.0 g of sodium hydroxide reacts with 30.0 g of sulfuric acid and 5.00 g of water is produced, what is the percent yield of the reaction? 23. A solution of potassium hydroxide has a mass of 50.0 g and contains 70.0 % water is neutralized by 20.0 g of sulfuric acid. What is the limiting reagent? Justify your answer.
Cooking with Stoichiometry You and a partner need to select one of the following recipes of cookies or bars to make at home. You then need to make all the conversions from the metric system (grams, ml, etc.) to the imperial system (cups, teaspoon, etc.) of measurement. Once you have made the conversions and shown all your work, the calculations need to be approved by Mr. Ziller or Mr. Malpert. When the conversions are approved you need to make the cookies or bars at home and bring enough for everyone in the class to sample. HINTS: Make sure your conversions are able to make a minimum of 36 cookies. A recipe can only be used ONCE per class period. Vanilla extract can be used in any recipe that calls for vanilla. Butter should always be softened, unless otherwise stated. Butter for baking should be UNSALTED Helpful Conversions: Tbs = Tablespoon tsp = teaspoon oz = ounces Ingredient U.S. Metric Ingredient U.S. Metric Ingredient U.S. Metric All-purpose Ground Pecans, 1 cup 99.37 g 1 tsp 1.972 g 1 cup 120.7 g flour cloves chopped Baking Lemonade 1 tsp 3.746 g 0.25 oz 7.087 g Raisins 1 cup 151.4 g powder flavoring Lemon Baking soda 1 tsp 4.288g 1 tsp 4.929 ml Salt 1 tsp 5.028 g extract Semisweet Brown 1 cup 201.1 g M&M s 12 oz 340.2 g chocolate 12 oz 340.2 g sugar chips Butter 1 cup 229.5 g Macadamia nuts, chopped 1 oz 28.34 g Semisweet chocolate chips 1 cup 179.8 g Cinnamon 1 tsp 2.514 g Milk 1 Tbs 14.79 ml Shortening 1 cup 229.5 g Sugar, Powdered 1 cup 130.1 g Molasses 1 cup 236.6 ml granulated 1 cup 191.6 g sugar sugar Cornstarch 1 cup 151.4 g Nutella 1 cup 296.0 g Vanilla 1 tsp 4.929 ml Cocoa Walnuts, 1 Tbs 6.95 g Oats, rolled 1 cup 80.44 g 1 cup 115.9 g powder chopped Cream of tartar 1 tsp 3.155 g Ginger 1 tsp 2.514 g Peanuts, chopped Peanut butter 1 cup 160.9 g Water 1 Tbs 14.79 ml 1 cup 179.8 g Additional Conversions: 3 tsp = 1 Tbs 16 Tbs = 1 cup Analysis Questions: White chocolate chips 1 cup 179.8 g 1. Describe the significance of stoichiometry to cooking. Think of other real life cooking examples where using the correct amount of ingredients is vital to a successful product. 2. Why don t we call it stoichiometry when we bake? 3. Hypothetically, what would happen if the instructor had made a miscalculation in the amount of ONE ingredient in your recipe? Think about how this would affect your recipe for each ingredient. 4. Theorize how you could increase the number of cookies made without changing the size of the cookies or quantity of ingredients? 5. Develop a hypothesis that would explain what the pharmaceutical world would be like without stoichiometry. Extra Credit: (15 pts) SHOW ALL YOUR WORK!!! Convert your recipe so all the starting ingredients are listed in moles. You will need additional resources.
Oatmeal-Raisin Cookies Prep: 25 minutes Bake: 8 minutes/batch Oven: 375 F Makes: about 48 cookies 172.1g softened butter 201.1g packed brown sugar 95.8g granulated sugar 3.746g baking powder 1.072g baking soda 1.257g salt 149.1g all-purpose flour 160.9g rolled oats 151.4g raisins 1. Preheat oven to 375 F. In a mixing bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add brown sugar, granulated sugar, baking powder, baking soda, and salt. Beat until combined, scraping sides of bowl. Beat in eggs and vanilla. Beat in as much of the flour as you can. Stir in remaining flour. Stir in rolled oats. Stir in raisins. 2. Drop dough by rounded teaspoons 2 inches apart onto an ungreased cookie sheet. Bake for 8 to 10 minutes or until edges are light brown. Cool on cookie sheet 1 minute. Transfer to a wire rack and let cool. Chocolate Chip Cookies Prep: 40 minutes Bake: 8 minutes/batch Oven: 375 F Makes: about 60 cookies 172.1g softened butter 57.38g shortening 201.1g packed brown sugar 95.8g granulated sugar 3.216g baking soda 2.514g salt 248.4g all-purpose flour 340.2g package semisweet chocolate chips 1. Preheat oven to 375 F. In a large mixing bowl beat butter and shortening with an electric mixer on medium to high speed for 30 seconds. Add the brown sugar, granulated sugar, baking soda, and salt. Beat until mixture is combined, scraping sides of bowl. Beat in eggs and vanilla until combined. Beat in as much flour as you can with the mixer. Stir in remaining flour. Stir in chocolate pieces. 2. Drop dough by rounded teaspoons 2 inches apart onto an ungreased cookie sheet. Bake for 8 to 9 minutes or until edges are light brown. Transfer to wire rack and allow to cool. Peanut Butter-Oatmeal Rounds Prep: 30 minutes Bake: 10 minutes/batch Oven: 375 F Makes: about 48 cookies 172.1g softened butter 89.9g peanut butter 191.6g granulated sugar 100.6g packed brown sugar 3.746g baking powder 2.144g baking soda 124.2g all-purpose flour 160.9g rolled oats 160.9g chopped cocktail peanuts 1. Preheat oven to 375 F. In a large mixing bowl beat butter and peanut butter with an electric mixer on medium to high speed about 30 seconds or until combined. Add granulated sugar, brown sugar, baking powder, and baking soda. Beat until combined, scraping sides of bowl occasionally. Beat in eggs and vanilla until combined. Beat in as much flour as you can with the mixer. Stir in any remaining flour. Stir in rolled oats and peanuts. 2. Drop dough by rounded teaspoons 2 inches apart onto an ungreased cookie sheet. Bake about 10 minutes or until edges are light brown. Transfer to a wire rack and allow to cool.
Snickerdoodles Prep: 25 minutes Bake: 10 minutes/batch Oven: 375 F Makes: about 36 cookies 114.8g softened butter 191.6g sugar 1.072g baking soda 0.7888g cream of tartar 1 egg 2.465mL vanilla 149.1g all-purpose flour 23.95g sugar 2.514g ground cinnamon 1. In a medium mixing bowl beat butter with an electric mixer for 30 seconds. Add the 1 cup of sugar, baking soda, and cream of tartar. Beat until combined, scraping sides of bowl occasionally. Beat in egg and vanilla until combined. Beat in as much flour as you can with the mixer. Stir in any remaining flour. Cover and chill dough about 2 hour or until easy to handle. 2. Preheat oven to 375 F. Combine the 2 tablespoons sugar and the cinnamon. Shape dough into 1-inch balls. Roll balls in sugar mixture to coat. Place 2 inches apart on an ungreased cookie sheet. Bake 10 to 11 minutes or until edges are golden. Transfer to wire rack and allow to cool. Sandies Prep: 25 minutes Bake: 15 minutes/batch Oven: 325 F Makes: about 48 cookies 229.5g softened butter 65.05g powdered sugar 14.79g water 198.7g all-purpose flour 181.1g cups finely chopped pecans 130.1g powdered sugar 1. Preheat oven to 325 F. Beat butter with an electric mixer on medium to high speed for 30 seconds. Add the ½ cup powdered sugar. Beat until combined, scraping sides of bowl. Beat in water and vanilla until combined. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour. Stir in pecans. 2. Shape dough into 1-inch balls. Place 1 inch apart on an ungreased cookie sheet. Bake about 15 minutes or until bottoms are light brown. Transfer to a wire rack and let cool. Place the 1 cup powdered sugar in a plastic bag; gently shake cooled cookies in bag to coat. Old-Fashioned Sugar Cookies Prep: 30 minutes Bake: 9 minutes/batch Oven: 375 F Makes: about 48 cookies 229.5g softened butter 287.4g sugar 3.155g cream of tartar 4.288g baking soda 1.257g salt 273.3g cups all-purpose flour 47.9g sugar 1. In a large mixing bowl beat the butter with an electric mixer on medium to high speed for 30 seconds. Add the 1 ½ cups sugar; beat until combined. Beat in the eggs, cream of tartar, baking soda, vanilla, and salt until combined. Beat in as much of the flour as you can with the mixer. Stir in the remaining flour. Cover and chill for 2 to 3 hours. 2. Preheat oven to 375 F. Shape dough into 1-inch balls. Roll balls in the ¼ cup sugar to coat. Place balls 2 inches apart on an ungreased cookie sheet. 3. Bake for 9 to 12 minutes or until light brown. Transfer to wire rack and allow to cool.
Peanut Butter Cookies Prep: 25 minutes Bake: 7 minutes/batch Oven: 375 F Makes: about 36 cookies 114.8g softened butter 89.9g peanut butter 95.8g granulated sugar 100.6g packed brown sugar 2.144g baking soda 1.873g baking powder 1 egg 2.465mL vanilla 124.2g all-purpose flour 1. Beat butter and peanut butter with an electric mixer on medium to high speed for 30 seconds. Add the granulated sugar, brown sugar, baking soda, and baking powder. Beat until combined, scraping the sides of bowl. Beat in the egg and vanilla until combined. Beat in as much flour as you can with the mixer. Stir in remaining flour. If necessary, cover and chill dough until easy to handle. 2. Preheat oven to 375 F. Shape dough into 1-inch balls. Roll balls in additional granulated sugar to coat. Place balls 2 inched apart on an ungreased cookie sheet. Flatten by making crisscross marks with the tines of a fork. Bake for 7 to 9 minutes or until bottoms are light brown. Transfer to wire rack and allow to cool. Peanut Butter Blossoms Prep: 25 minutes Bake: 10 minutes/batch Oven: 350 F Makes: about 54 cookies 114.8g shortening 89.9g peanut butter 95.8g granulated sugar 100.6g packed brown sugar 3.746g baking powder 0.536g baking soda 1 egg 29.58mL milk 173.9g cup all-purpose flour 47.9g granulated sugar Milk chocolate kisses or stars (~54) 1. Preheat oven to 350 F. In a large mixing bowl beat shortening and peanut butter with an electric mixer on medium to high speed for 30 seconds. Add the ½ cup granulated sugar, brown sugar, baking powder, and baking soda. Beat until combined, scraping sides of bowl occasionally. Beat in egg, milk, and vanilla until combined. Beat as much of the flour as you can with the mixer. Stir in any remaining flour. 2. Shape dough into 1-inch balls. Roll balls in the ¼ cup granulated sugar. Place 2 inches apart on an ungreased cookie sheet. Bake for 10 to 12 minutes or until edges are firm and bottoms are light brown. Immediately press a chocolate kiss into each cookie s center. Transfer to a wire rack and allow to cool. Chocolate Chocolate Chip Cookies Prep: 15 minutes Bake: 10 minutes Oven: 350 F Makes: about 48 cookies 229.5g softened butter 74.13g cocoa powder 3.216g baking soda 1.257g salt 287.4g cup sugar 9.858mL vanilla 198.7g all-purpose flour 359.6g semisweet chocolate chips 1. Preheat oven to 350 F. In a large bowl beat butter, sugar, eggs, and vanilla until light and fluffy. In a separate bowl, combine the flour, cocoa, baking soda, and salt. Stir into the butter mixture until well blended. Mix in the chocolate chips. Drop by rounded teaspoon onto ungreased cookie sheets. 2. Bake for 8 to 10 minutes until cookie just becomes set. Cool on tray for 1 minute and then transfer to wire rack and allow to cool.
Ginger Cookies Prep: 15 minutes Bake: 10 minutes Oven: 350 F Makes: about 48 cookies 447.2g cups all-purpose flour 7.542g and 2.514g ginger 8.576g baking soda 3.771g ground cinnamon 1.972g ground cloves 2.514g salt 344.3g softened butter 383.2g sugar 29.58mL water 118.3mL molasses 47.9g white sugar 1. Preheat oven to 350 F. In a medium bowl, sift together the flour, ginger, baking soda, cinnamon, cloves, and salt. Set aside for later. 2. In a large bowl, cream together the butter and 2 cups sugar until light and fluffy. Beat in the egg, then stir in the water and molasses. Gradually stir in sifted ingredients into the molasses mixture. Shape dough into 1-inch balls and roll them in the remaining ¼ cup sugar. Place cookies 2 inches apart on ungreased cookie sheet, and flatten slightly. 3. Bake for 8 to 10 minutes. Allow cookies to cool on baking sheet for 5 minutes. Remove cookies and allow to cool completely on a wire rack. Russian Tea Cakes Prep: 20 minutes Bake: 12 minutes Oven: 350 F Makes: about 36 cookies 229.5g butter 198.7g all-purpose flour 115.9g chopped walnuts 48.79g confectioners sugar 43.37g confectioners sugar for decoration 1. Preheat oven to 350 F. In a medium bowl, cream butter and vanilla until smooth. Combine the 6 table spoons confectioners sugar and flour. Stir into the butter mixture until just blended. Mix in the chopped walnuts. Roll dough into 1-inch balls, and place them 2 inches apart on an ungreased cookie sheet. 2. Bake 12 minutes. Remove and allow to cool completely. When cool, roll cookie in remaining confectioners sugar until well coated. White Chocolate Macadamia Nut Prep: 15 minutes Bake: 10 minutes Oven: 350 F Makes: about 36 cookies 114.8g softened butter 150.8g packed brown sugar 114.8g shortening 1 egg 7.393mL vanilla 198.7g all-purpose flour 4.288g baking soda 2.514g salt 179.8g white chocolate chips 198.4g macadamia nuts, chopped 1. Preheat oven to 350 F. Beat butter and shortening until soft and creamy. Gradually add the sugars and beat well. Add egg and vanilla and beat well. Combine flour, baking soda, and salt. Gradually add to butter mixture beating well after each addition. Stir in white chocolate chips and macadamia nuts. 2. Drop dough by rounded teaspoons onto a lightly greased cookie sheet. Bake for 10 to 12 minutes or until edges turn light brown. Remove and place on wire rack and allow to cool.
M&M Cookies Prep: 40 minutes Bake: 8 minutes/batch Oven: 375 F Makes: about 60 cookies 172.1g softened butter 57.38g shortening 201.1g packed brown sugar 95.8g granulated sugar 3.216g baking soda 2.514g salt 248.4g all-purpose flour 340.2g package M&M s 1. Preheat oven to 375 F. In a large mixing bowl beat butter and shortening with an electric mixer on medium to high speed for 30 seconds. Add the brown sugar, granulated sugar, baking soda, and salt. Beat until mixture is combined, scraping sides of bowl. Beat in eggs and vanilla until combined. Beat in as much flour as you can with the mixer. Stir in remaining flour. Stir in M&M s. 2. Drop dough by rounded teaspoons 2 inches apart onto an ungreased cookie sheet. Bake for 8 to 9 minutes or until edges are light brown. Transfer to wire rack and allow to cool. Nutella Cookies Prep: 10 minutes Bake: 10 minutes Oven: 375 F Makes: about 36 cookies 114.8g softened butter 100.1g brown sugar 95.8g sugar 296.0g Nutella 198.7g all-purpose flour 4.288g baking soda 1.257g salt 6.95g cocoa powder 1. Preheat oven to 375 F. Line cookie sheets with parchment paper and set aside. In a small bowl combine flour, salt, cocoa powder, and baking soda; set aside. In a large mixing bowl, cream together the butter, brown sugar, and sugar. Add the egg, vanilla, and Nutella and mix until well combined. Add the dry ingredients and mix until dough well combined. 2. Drop dough by tablespoon on prepared cookie sheets 2 inches apart. Bake for 8 to 10 minutes. Allow to cool completely. Cookies will puff while baking, but will flatten out as they cool. Lemon Cookies Prep: 20 minutes Bake: 20 minutes Oven: 300 F Makes: about 36 cookies 99.37g all-purpose flour 75.7g corn starch 2.514g salt 65.05g confectioners sugar 172.1g softened butter 4.929mL lemon extract 130.1g confectioners sugar 7.087g package of unsweetened lemonade flavor drink mix (Koolaid, Crystal Light, etc.) 1. In a small to medium bowl sift the flour, cornstarch, and salt. In a larger bowl, beat ½ cup confectioners sugar with butter using an electric mixer until the mixture is creamy and free of lumps. Beat in the lemon extract, then mix in the flour to make a smooth dough. Chill dough for 1 hour. 2. Preheat oven to 300 F. Scoop about 1 ½ teaspoon of dough and roll into balls. Place cookie onto ungreased cookie sheet. Bake in the preheated oven for about 20 minutes, or until cookies are set. 3. While first batch of cookies are baking, mix 1 cup confectioners sugar with the lemonade drink mix in a plastic zipper bag. Close the zipper and shake the bag to blend sugar and drink mix. 4. After baking, remove cookies and allow to cool 2 minutes on cookie sheets. Drop 5 to 6 of the cookies into the bag of lemon sugar at a time, and shake to coat with the mixture. Shake off excess and place on wire rack and allow to cool. When cool, shake cookies one more time in the lemon sugar, lightly shaking off any excess.
Lab 27: Stoichiometry and Chemical Reactions: Which Balanced Chemical Equation Best Represents the Thermal Decomposition of Sodium Bicarbonate? Introduction The law of conservation of mass states that mass is conserved during a chemical reaction. The law of definite proportions states that a compound is always made up of the exact same proportion of elements by mass. John Dalton was able to explain these two fundamental laws of chemistry with his atomic theory, which states that a chemical reaction is simply the rearrangement of atoms with no atoms being destroyed and no new atoms being produced during the process. Chemists use a balanced chemical equation to represent what happens on the submicroscopic level during a chemical reaction. The stoichiometric coefficient is the number written in front of atoms, ions, or molecules in a chemical equation. These numbers are used to balance the number of each type of atom found on both the reactant and product sides of the equation. Stoichiometric coefficients are also useful because they identify the mole ratio between reactants and products. The mole ratio is important because it allows chemists to determine how many moles of a product will be produced from a specific number of moles of a reactant or how many moles of reactant are needed to produce a specific amount of product. Molar mass serves as a bridge between the number of moles of a substance and the mass of a substance. The molar mass is the mass of a given substance divided by one mole of the substance. The molar mass of a given substance can be calculated by summing the atomic mass for each atom found in a molecule of that substance. For example, the atomic mass of hydrogen is 1.01 g/mol, and the atomic mass of oxygen is 15.99 g/mol, so the molar mass of H2O is 18.01 g/mol (1.01 g/mol + 1.01 g/mol + 15.99 g/mol). Once the molar mass of a substance is known, the mass of a sample can be used to determine the number of moles of a substance or the moles of substance can be used to determine the mass of a sample. For example, a 40-gram sample of H2O consists of 2.20 mol of H2O (40.4 g H2O 18.01 g/mol = 2.20 mol of H2O) and a 3.0 mol sample of H2O has a mass of 54.0 g (3.00 mol of H2O x 18.01 g/mol =54.03 g of H2O). In this investigation, you will have an opportunity to use atomic theory, molar mass, and stoichiometry to determine how atoms are rearranged during a chemical reaction. Your Task There are at least four different balanced chemical equations that could explain how atoms are rearranged during the thermal decomposition of sodium bicarbonate (NaHCO3). The first potential explanation is that the sodium bicarbonate decomposes into sodium hydroxide (NaOH) and carbon dioxide (CO 2 ) when it is heated. The balanced chemical equation for this reaction is NaHCO 3(s) NaOH (s) + CO 2(g) The second potential explanation is that sodium bicarbonate decomposes into sodium carbonate (Na 2 CO 3 ), carbon dioxide (CO 2 ), and water (H 2 O) when it is heated. The balanced chemical equation for this potential reaction is 2NaHCO 3(s) Na 2 CO 3(s) + CO 2(g) + H 2 O (g) The third potential explanation is that the sodium bicarbonate decomposes into sodium oxide (Na 2 O), carbon dioxide (CO 2 ), and water (H 2 O) when it is heated. The balanced chemical equation for this potential reaction is 2NaHCO 3(s) Na 2 O (s) + 2CO 2(g) + H 2 O (g) The fourth potential explanation is that the sodium bicarbonate decomposes into sodium hydride (NaH), carbon monoxide (CO), and oxygen (O 2 ) when it is heated. The balanced chemical equation for this potential reaction is NaHCO 3(S) NaH (s) + CO (g) + O 2(g) Your goal is to determine which of these four balanced chemical equations best represents how atoms are rearranged during the thermal decomposition of sodium bicarbonate. The guiding question of this investigation is, Which balanced chemical equation best represents the thermal decomposition of sodium bicarbonate?
Materials You may use any of the following materials during your investigation: Consumables Solid NaHCO 3 Equipment Bunsen burner Lighter Ring stand with metal ring Crucible with lid Crucible tongs Clay triangle Wire gauze square Electronic balance Periodic table Safety Precautions Follow all normal lab safety rules. Your teacher will explain relevant and important information about working with the chemicals associated with this investigation. In addition, take the following safety precautions: Wear indirectly vented chemical-splash goggles Use caution when working with Bunsen burners. They can burn skin, and combustibles and flammables must be kept away from the open flame. If you have long hair, tie it back behind you head. Inspect crucible for cracks. Exchange cracked or broken crucibles for a new one. Wipe crucible and lid clean before using them. Be careful with a crucible after removing it from a flame it will be extremely hot. Handle all glassware with care. Wash your hands with soap and water before leaving the laboratory. Investigation Proposal Required? Yes No Getting Started As part of your investigation, you will need to use a Bunsen burner and a crucible (see Figure L27.1) to increase the temperature of sodium bicarbonate enough for it to decompose. The thermal decomposition of sodium bicarbonate will occur rapidly at 200 C, but the product of the decomposition reaction will begin to decompose at temperatures over 850 C. To answer the guiding question, you will need to design and conduct an investigation. To answer the guiding question, you will also need to determine what type of data you will need to collect during your investigation, how you will collect the data, and how you will analyze the data. To determine what type of data you need to collect, think about the following questions: o How much NaHCO3 will you need to use? o What will you need to measure? To determine how you will collect the data, think about the following questions: o How long will you need to heat the NaHCO3? o How will you empirically determine when the decomposition of the NaHCO3 is complete? o How will you reduce error? To determine how you will analyze the data, think about the following questions: o What type of calculations will you need to make? o How will your group take into account the precision of the balance in your analysis? FIGURE L27.1 How to heat sodium bicarbonate using a crucible and a Bunsen burner
Connections to Crosscutting Concepts As you work through your investigation, be sure to think about the importance of identifying patterns, which proportional relationships are critical to the understanding of this investigation, how scientific knowledge changes over time in light of new evidence, and the difference between data and evidence. Initial Argument Once your group has finished collecting and analyzing your data, you will need to develop an initial argument. Your argument must include a claim, which is your answer to the guiding question. Your argument must also include evidence in support of your claim. The evidence is your analysis of the data and your interpretation of what the analysis means. Finally, you must include a justification of the evidence in your argument. You will therefore need to use a scientific concept or principle to explain why the evidence that you decided to use is relevant and important. You will create your initial argument on a whiteboard. Your whiteboard must include all the information shown in Figure L27.2. FIGURE L27.2 Argument presentation on a whiteboard Argumentation Session The argumentation session allows all of the groups to share their arguments. One member of each group stays at the lab station to share that group s argument, while the other members of the group go to the other lab stations one at a time to listen to and critique the arguments developed by their classmates. The goal of the argumentation session is not to convince others that your argument is the best one; rather, the goal is to identify errors or instances of faulty reasoning in the initial arguments so these mistakes can be fixed. You will therefore need to evaluate the content of the claim, the quality of the evidence used to support the claim, and the strength of the justification of the evidence included in each argument that you see. To critique an argument, you might need more information that what is included on the whiteboard. You might, therefore, need to ask the presenter one or more of the following questions, such as: How did your group collect the data? Why did you use that method? What did your group do to make sure the data you collected are reliable? What did you do to decrease measurement error? What did your group do to analyze the data, and why did you decide to do it that way? Did you check your calculations? Is that the only way to interpret the results of your group s analysis? How do you know that your interpretation of the analysis is appropriate? Why did your group decide to present your evidence in that manner? What other claims did your group discuss before deciding on that one? Why did you abandon those alternative ideas? How confident are you that your group s claim is valid? What could you do to increase your confidence? Once the argumentation session is complete, you will have a chance to meet with your group and revise your original argument. Your group might need to gather more data or design a way to test one or more alternative claims as part of this process. Remember, your goal at this stage of the investigation is to develop the most valid or acceptable answer to the research/guiding question!
Report Once you have completed your research, you will need to prepare an investigation report that consists of three sections that provide answers to the following questions: 1. What question were you trying to answer and why? 2. What did you do during your investigation and why did you conduct your investigation in this way? 3. What is your argument? Your report should answer these questions in four pages or less. The report must be typed and any diagrams, figures, or tables should be embedded into the document. Be sure to write in a persuasive style; you are trying to convince others that your claim is acceptable and valid!
Investigation Timeline Option D Stage 1: Identify the task and the guiding question. Hold a tool talk Day 1 Small groups of students then 50 Minutes Stage 2: Design a method and collect data Groups then Stage 3: Analyze data and develop a tentative argument Day 2 Each group then shares its argument during an Stage 4: Argumentation session If needed, groups can Collect additional data or reanalyze the collected data 50 Minutes The teacher then leads an The teacher then leads an Stage 5: Explicit and reflective discussion Homework Individual students then Stage 6: Write and investigation report Day 3 The report then goes through a Stage 7: Double-blind group peer review 30 Minutes Homework Each student then Stage 8: Revises and submits his or her report
Investigation Proposal A The guiding question IF Hypothesis 1 Hypothesis 2 IF AND Procedure The Test What data will you collect? How will you analyze the data? What safety precautions will you follow? Predicted Result if hypothesis 1 is valid THEN Predicted result if hypothesis 2 is valid THEN AND The Actual Results I approve of this investigation. Instructor s Signature Date