Stoichiometry is Cooking
Stoichiometry is Cooking
5E Lesson Plan, Author: Sara Rosario, Yakima WATERS Project, CWU, Fall 2010
Stoichiometry is the quantitative relationship between the reactants and productions in a chemical reaction. Stoichiometry involves indentifying proportional relationship between reactants and products, to alter stoichiometric coefficients to balance chemical equation and to use stoichiometric coefficients to obtain quantitative information. In this lesson students will learn Stoichiometry, by first examining the proportions of ingredients in cookie recipes then by balancing chemical equations, calculating limiting reagents, and theoretical yields. This lesson is appropriate for 11th and 12th graders and should take an hour to an hour and 20 minutes to complete.
Standards
Science standards for Matter: properties and change
9-11 PS2E - Molecular compounds are composed of two or more elements bonded together in a fixed proportion by sharing electrons between atoms, forming covalent bonds. Such compounds consist of well-defined molecules. Formulas of covalent compounds represent the types and number of atoms of each element in each molecule
9-11 PS2G - Chemical reactions change the arrangement of atoms in the molecules of substances. Chemical reactions release or acquire energy from their surroundings and result in the formation of new substances.
Math standards
A1.8.A - Analyze a problem situation and represent it mathematically.
A1.8.C - Evaluate a solution for reasonableness, verify its accuracy, and interpret it in the context of the original problem.
A1.3B. - Represent a function with a symbolic expression, as a graph, in a table, and using words, and make connections among these representations.
A1.8.G - Synthesize information to draw conclusions and evaluate the arguments and conclusions of others.
Outcomes
Upon completion students should be able to identify proportional relationships between reactants and products (Ex: if there are 2 moles of oxygen in the reactant then student should be able to determine that there should be 2 moles of oxygen in the products) and see how changes in the stoichiometric ratios affect the outcome of a reaction in this case their cookies. At the end of this lesson students should also be able to balance chemical equations, obtain quantitative information such as moles and mass from chemical equations, and find limiting reagents and theoretical yields.
Materials and Equipment
For 36 students you will need 10 lbs flour, 5lbs granulated sugar, 5 lbs brown sugar, 5 lbs semi-sweet chocolate chips, 2 dozen eggs and a large package of rolled oats. For the rest of the dry ingredients you will need a pound of each, for the wet ingredients you will need at least 12 ounces of each.
Food stuff: Flour, sugar, butter, eggs, rolled oats, chocolate chips, coco powder, shredded coconut, walnuts, almonds, dried cranberries, peanut butter, honey, hot water, vanilla extract, baking soda.
Utensils: large mixing bowls, small microwave safe bowls, wooden spoons, measuring cup and measuring spoons, aluminum foil, hot plates, small sauce pans or small pots and electronic balances. You will need access to an oven or to two or three tosterovens and microwave ovens.
Cookie recipes are in resources section. Please note that all the recipes converted to grams measurement to make the math easier.
Prior Knowledge
Students must also know the law of conservation of mass. Students should be able to perform simple arithmetic and be able to multiply and divide fractions prior to this lesion. Students should have had significant exposure to chemical equations. It may also be helpful for students to be able to perform determinants and combine algebraic equations.
Safety
In this lesson student will be asked to make cookies, be sure to ask students about food allergies. And alter recipes as needed. Also be sure to supervise students with ovens.
Engage (10 min)
In the resources section you will find the Grilled Cheese Sandwich Stoichiometry Formative assessment. This is fun assessment that can be used as either a formative assessment or an introductory activity to get students started thinking about stoichiometry.
Explore (15 min)
Pairs of students will be giving a recipe and ingredients and utensils (you may find it help full to have bags of premeasured ingredients with the ingredient name and quantity written on the bag, wooden spoons and measuring utensils with the mixing bowl). You can either tell students that they must alter their recipe to make a ½ dozen cookies or you may decrease the quantity of one ingredient and have the students adjust the recipes to match. I personally prefer the latter as it more closely resembles common stoichiometry problems. You can also have all the students prepare variations of the same recipe. For example group I no variations, groups II use 5 g (1 teaspoon) baking powder instead of two, group III use 10 g (2 teaspoons) baking soda instead of baking powder, group IV use one egg, group V use no eggs and group VI use 180 ml (3/4 cup) butter instead of 60 ml (1/4 cup). Have the students work out their recipe stoichiometry on a separate sheet of paper. This is a good place to introduce students to limiting reagents and theoretical yields by having students determine the limiting reagent and calculate theoretical yield. Be sure they know they must use all of the ingredients mentioned in the recipe. Once they have completed their alteration check their work and have them make their cookies. When their cookies are ready to bake you may needed to transport the cookies to the oven or assist student with the toaster ovens. When the cookies are done baking and cooling students will be asked asses the success of their recipe see rubric below. While cookies are baking do the explain portion of this lesson.
Explain (10 min)
Have students explain how they altered their cookie recipes, what was their line or reasoning, how did they determine the amounts of each ingredient to be used and how they think the changes will affect the final product. If students devised different methods to alter the recipes have them share their method with the class. Ask students to compare the amounts of each ingredient in their recipes before and after baking, one way to do this is to have students calculate the mass of each ingredient in one cookie. Ask student to account for all ingredients in the cookies; were there any gains or losses in the amounts of each ingredient? It is especially important that students understand the relationship between the ingredients in the finished cookies. The proportion of each ingredient should be the same in the recipe and finished cookie. Please refer to the proportional recipes in the resources section as these recipes give the ratio of mass of each ingredient in one cookie.
Extend/Elaborate (20 min)
Next explain to the student that what they did was stoichiometry (it may be helpful to write out the cookie recipes like a chemical equation). Define Stoichiometry and the rules of stoichiometry. Explain what stoichiometric coefficients are and be sure to relate the coefficients to the amount (moles or mass) of ingredients in recipes or chemical reactions. It is extremely important that students understand that stoichiometric coefficients represent numbers of molecules not quantities such as grams or liters. For example;
3H2 + N2 → 2NH3
The reaction above can be read as 3 molecules of H2 plus 1 molecule N2 yields 2 molecules of NH3. Or you can read the reaction as 3 dozen H2 plus 1 dozen N2 yields 2 dozen NH3. Stiochoimetric coefficients represent proportion of each atom involved in the chemical reaction. Have the students work with you to balance two or three simple chemical equations. As a class work thru some limiting reagent and theoretical yield problems, when this is done give the students the stoichiometry is cooking worksheets attached and have them do it. On this worksheet students must they must balance chemical equations; find theoretical yields and limiting reagents of chemical reactions and recipes.
Evaluate (10 min)
Students will be asked to evaluate their finished cookies using the student cookie rubric provided below. Ask students to think about how alterations in amount of ingredients may have affected the cookies and how they might improve the recipes for the future. Students will also be asked to turn in their worksheets, this worksheet can be graded using the rubric. If you have only 50 minute to complete this lesson student may work their worksheet at home and turn it in later.
Property / DescriptionMoisture
Texture
Consistency
Dimensions
(height and diameter)
Taste
Performance Rubric
(5pts) / Good
(4pts) / In Development (3pts) / Needs Rethinking (2pts) / Not Scorable
(1pt)
Conceptual Understanding
(1, 20%) / Student should get questions 5, 9 and 10 correct. On question 4 students should be able to provide a logically explanation of the steps they took to solve the problem. / Student may answer one question (Qs 5, 9 and 10) incorrectly. On question 4 students should be able to provide a muddy explanation of the steps they took to solve the problem. / Student may answer two questions (Qs 5, 9 and 10) incorrectly. On question 4 student should be able to provide a muddy explanation of the steps they took to solve the problem.. / Student may answer questions 5,9 and 10 incorrectly. On question 4 student may not be able to provide a sensible explanation of the steps they took to solve the problem. / Student may answer all three questions incorrectly. On question 4 student did not provide any explanation of the steps they took to solve the problem.
Skill 1, Balancing Chemical Equations (1, 20%) / Student is able to apply stoichiometry to balance chemical. This means the student answers question 2, 4 and 5 correctly on the student work sheet. On question 4 the student should be able to provide a logical explanation as to why they chose the coefficients values they chose. / The student may answers one of question 2, 4 and 5 incorrectly. On question 4 the student should be able to provide a logical explanation as to why they chose the coefficients values they chose. / The student may answers two of question 2, 4 and 5 incorrectly. On question 4 the student should be able to provide a muddy explanation as the coefficients they chose. / Student may answer all three questions incorrectly. On question 4. Student may not be able to provide a sensible explanation of the coefficient they chose. / Student may answer all three questions incorrectly. On question 4. Student did not provide any explanation of the steps they took to solve the problem.
Skill 2, Calculating Mass and moles from stoichiometric coefficients (2, 20%) / The student is able to correctly answer question 3 correctly. And is able to provide a logical explanation of the steps they took to solve the problem. / The student is not able to correctly answer question 3 correctly. And is able to provide a muddy explanation of the steps they took to solve the problem. / The student is not able to correctly answer question 3 correctly. And is unable to provide any explanation of the steps they took to solve the problem.
Skill 3, Calculating limiting reagent and theoretical Yield (3, 40%) / The student should be able to answer question 1,4,5,6,7 and 8 correctly . / The student should be able to answer question 1,4,6,7 and 8 correctly. / The student should be able to answer question 1,4,7 and 8 correctly. / The student should be able to answer question 1 and 4 correctly. / The student cannot answer question 1,4,5,6,7 and 8 correctly.
Teacher Background Info
Stoichiometry is the quantitative relationship between the reactant and products of a chemical reaction. Stoichiometry is used to balance chemical equations and there are a few assumptions that must be made about the chemical reactions to do this. Assumption one: all reagents are consumed in the reaction. Assumption two: no side reactions occur and assumption three: no atoms are lost in the reaction.
Resources
Recipes
ANZAC Biscuits:
128 g Flour
85 g Rolled oats
220 g Brown sugar
71 g shredded coconut
46 g Almonds
46 g Cranberries
57 g Butter
43 g Honey
30 g Water
Mix together flour, brown sugar, rolled oats, shredded coconut, almonds and cranberries in a large mixing bowl until combined and set aside. In a pot place butter, honey and water, place on hot plate and heat until everything is melted. After melting stir and pour the melted mixture into the mixture of dry ingredients. Mix until all ingredients are combined. Roll dough into 15g (about one inch in diameter) balls, place the dough balls onto a baking sheet at least 1 ½ inches apart. Bake for 10 minutes at 350⁰C. Makes 4 Dozen Cookies.
Oatmeal Chocolate Cookies:
256 g Flour
43 g Rolled Oats
227 g Butter 2 Eggs
46 g Walnuts
150 g Sugar
165 g Brown Sugar
228 g Chocolate Chips
12 g Baking Soda
15 g Vanilla
Mix butter, sugar, brown sugar in a large mixing bowl, until the mixture appears fluffy and creamy. Add eggs and vanilla and stir until combined. Now add now add flour, oats and baking powder, stir to combine. Add walnuts and chocolate chip and stir to combine. Roll dough into 19.8 g (about one inch in diameter) balls place the dough balls onto a baking sheet about 1 ½ inches apart. Bake for 12 minutes at 350⁰C. Makes 5 dozen cookies.