Stoichiometry and Limiting Reagent
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Created on October 30, 2021
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Transcript
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Stoichiometry and Limiting Reagent
Poster-Lab 4
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Introduction
Introduction Stoichiometry is a section of chemistry that involves the relationship among reactants and/or products in a chemical reaction to “determine desired quantitative data”. (Nijmeh J. 2020) In order to use stoichiometry it is necessary to understand the relation between reactants and products. For example, we use stoichiometry in the balancing of reactions. There must be the same number of atoms in the two sides of a chemical equation, since the Law of Conservation of Mass states that “matter is neither created nor destroyed in a chemical reaction”. When there is not enough of one reactant in a chemical equation, the reaction stops abruptly. To prevent this, we must find the limiting reagent, which is the reactant that will stop the reaction and we also have to find if there is any reactant excess, “one way of finding the limiting reagent is by calculating the amount of product that can be formed by each reactant”.
Objective/ hypothesis
Objective Students will apply the concepts of stoichiometry and limiting reagents to adjust the quantity of ingredients in a recipe. Research question How can we apply the concepts of stoichiometry and limiting reagent in the process of making cookies? Hypothesis If we adjust the quantity of ingredients in a recipe of cookies, then we will get a different number of cookies. Independent variable: Quantity of ingredients Dependent variable: Number of cookies Controlled variables: Size of the cookies, time in the oven, heat, the amount of dough used for a cookie
Methodology /Flow chart
Materials, equipment and methodology 1 cup= 150 gr 1 teaspoon=5 gr 1 pound=453.6 gr 1 tbsp=10 gr • 453.6 gr of unsalted butter • 262.5 gr granulated sugar • 337.5 gr cups of brown sugar • 4 eggs • 900 gr plus 20 gr of flour • 5 gr of salt • 10 gr of baking powder • 10 gr of sodium bicarbonate • 5 ml of vanilla extract • 907.2 gr of milk or dark chocolate, chopped or in chips Note: This recipe yields 25 cookies 1. Convert units into mass (g) or volume (mL) using a conversion chart. 2. Adjust the recipe to obtain 12 cookies and add the chart in results. 3. Record the video showing the procedure described below: https://www.marthastewart.com/314346/jacques-torress-secret-chocolate-chip-co 4. Imagine there is not enough flour, and you only have 3 cups. How would this affect the quantities expressed in the recipe? How do you relate this to the concept of limiting reagent? Explain this in the results analysis. Indicate how many cookies will be obtained from this amount of flour. The flour would be the limiting reagent since it would impede the making of the cookies. Then we would have to make an adjustment so all the ingredients in the recipe allow us to make the cookies. There would be less cookies since we had less ingredients. In chemical terms, when the reactant decreases, the products will also decrease. If we perform the calculations to adjust the recipe for 3 cups of flour (450*25)/920, at the end we will have 12 cookies. 920 gr of flour corresponds to 25 cookies, 450 gr corresponds to 12 cookies. Table 1 Ingredients Original ingredients for 25 cookies Operation performed Adjustment for 12 cookies 453.6 gr of unsalted butter (453.6*12)/25=217.7 217.7 gr 262.5 gr granulated sugar (262.5*12)/25=125 126 gr 337.5 gr of brown sugar (337.5*12)/25=162 162 gr 4 eggs (4*12)/25=1.9 1.9 pieces 900 gr plus 20 gr of flour (900*12)/25=423 (20*12)/25=9.6 423 gr 9.6 gr 5 gr of salt (5*12)/25=2.4 2.4 gr 10 gr of baking powder (10*12)/25=4.8 4.8 gr 10 gr of sodium bicarbonate (10*12)/25=4.8 4.8 gr 5 ml of vanilla extract (5*12)/25=2.4 2.4 ml 907.2 gr of milk or dark chocolate, chopped or in chips (907.2*12)/25=435.5 435.5 gr Table 1. Measurements of original recipe for 25 cookies and procedures to obtain the adjustment for 12 cookies. Flowchart
Results
Link to team videos: https://drive.google.com/drive/folders/13c5WFbqqZNwOD0Pfk8M9Mv6aQWz_YaFo?usp=sharing
Analysis/Discussion
Discussion During the experiment, we all followed the same recipe and used the same ingredients in the same quantities, which we got from converting the measurements that were originally called for and scaling them down to about half of what they were. Though the conditions were the same for all team members, we yielded slightly different results from one another. Notably, depending on the space that was left between the scoops of cookie dough, some of us ended up with large cookies that joined together while cooking as a result of the dough expanding. The colours also varied a bit but from what we could gather the flavours were all more or less the same which was to be expected. “ At about 212 degrees Fahrenheit, the water in the dough turns into steam. The cookie starts to rise as the vapours push through the dough. Eventually, the baking soda or powder starts to break down into carbon dioxide gas, which raises up the cookie farther.” (Doucleff, 2013) Just as the cookie is almost finished baking there's caramelization, which means as sugars in the dough break down, they transform from clear, odourless crystals into a brown, fragrant liquid. Then the “Maillard reaction” packs the cookie with even richer tastes and helps darken its surface. Imagine there is not enough flour, and you only have 3 cups. How would this affect the quantities expressed in the recipe? How do you relate this to the concept of limiting reagent? The flour would be the limiting reagent since it would impede the making of the cookies. Then we would have to make an adjustment so all the ingredients in the recipe allow us to make the cookies. There would be fewer cookies since we had fewer ingredients. In chemical terms, when the reactant decreases, the products will also decrease. If we perform the calculations to adjust the recipe for 3 cups of flour (450*25)/920, at the end we will have 12 cookies. 920 gr of flour corresponds to 25 cookies, 450 gr corresponds to 12 cookies.
Conclusion
Conclusion Throughout the development of practice, we could assert that the hypothesis was proven right since when we adjusted the quantities of ingredients in the recipe, this directly affected the number of products which were the cookies in question. This last is due to the fact that the dependent variable is related to the independent one. Furthermore, the objective was accomplished as the experiment clearly illustrates the application of stoichiometry knowledge as well as the limiting reagent which, in this case, was the flour. In conjunction, these all demonstrate the connection between the mentioned concepts. Finally, taking into consideration the errors once made through the practice, we identified that it is a must to accurately measure the quantities of the ingredients as if we use different amounts we could get distinct results and the cookies would not turn out as expected in terms of size, shape and even consistency. Along with it, the type of chocolate is really important since if it has a really soft consistency, it would totally mix within the dough. Additionally, it is of great importance that we do not open the oven before the established baking time as it can affect the process reaction within the substances involved in its cooking.
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Aleida Martínez Saldaña A01751299Isabella Saldaña Rivera A01752858Aurora Gutiérrez Rodríguez A01752884Esteban Lara de la vega A01751809Emiliano Moreno Gómez A01751730
References
References Balancing Chemical Equations. (2020, August 13). University of Illinois at Chicago. Retrieved October 21, 2021 from https://chem.libretexts.org/@go/page/79558 Limiting Reagents. (2020, August 15). Retrieved October 21, 2021 from https://chem.libretexts.org/@go/page/236 Nijmeh J. Tye M. Stoichiometry and Balancing Reactions. (2020, August 15). Retrieved October 21, 2021 from https://chem.libretexts.org/@go/page/240 Meredith, B. (2018, July 23). Stoichiometry (article) | Chemical reactions. Khan Academy. Retrieved October 22, 2021, from https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:chemical-reactions/x2eef969c74e0d802:stoichiometry/a/stoichiometry Taylor-Jhonson, A. (2016, June 14). Limiting reactant and reaction yields (article). Khan Academy. Retrieved October 22, 2021, from https://www.khanacademy.org/science/ap-chemistrybeta/x2eef969c74e0d802:chemicalreactions/x2eef969c74e0d802:stoichiometry/a/limiting-reagents-and-percent-yield Libretexts. (2021, June 30). 12.9: Theoretical Yield and Percent Yield. Chemistry LibreTexts. Retrieved October 22, 2021, from https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK12)/12%3A_Stoichiometry/12.09%3A_Theoretical_Yield_and_Percent_Yield