Chem 105 Fall 2023 POGIL 2 Worksheet - Blank

1 Chem 105 POGIL Recitation 2 Sep. 14, 2023 Model 1: Balancing Chemical Reaction Equations and Stoichiometry Time: 15 minutes Learning objectives: • Follow the guidelines presented in lecture to produce a balanced chemical reaction equation. • Practice calculations related to the stoichiometry of a balanced chemical reaction equation. Iron (III) oxide (Fe 2 O 3 ) can react with carbon (C) to produce iron (Fe) and carbon dioxide (CO 2 ). Using this information and the guidelines presented in lecture for producing a balanced chemical reaction equation, answer the following questions as a group. 1. Following steps 1 and 2, write a preliminary equation showing all reactants and products and check to see if it is balanced. 2. If the reaction is not balanced, follow step 3 and balance an element that appears in one reactant and one product. 3. Following step 4, find coefficients for the remaining substances to achieve a complete balanced chemical reaction equation. 4. Determine the amount of Fe 2 O 3 ( in grams ) that were initially present if 1.84 moles of carbon dioxide were produced. You may assume the reaction proceeded entirely to completion (i.e., all of the reactants were completely converted to products). Show all work to support your answer. 5. In a very similar chemical process, Iron (III) oxide (Fe 2 O 3 ) can also react with carbon monoxide (CO) to produce iron (Fe) and carbon dioxide (CO 2 ). Using the guidelines presented in lecture, provide a balanced chemical equation for this reaction .

2 Model 2: Determining the Empirical Formula from Percent Composition Data Time: 20 minutes Learning objectives: • Understand the definitions of empirical formula, molecular formula, and percent composition by mass. • Practice calculations using percent composition by mass data to produce empirical formula. • Practice calculations using molecular mass (determined by mass spectrometry) to determine molecular formula. A compound is known to contain only carbon (C), hydrogen (H) and nitrogen (N). The plot at the right shows the percent composition by mass of the elements H and N. Using this information and your lecture notes, answer the following questions as a group. 6. a) What is the percent composition by mass of H and N? Record your answers on the lines provided below. H: ______________________ N: ______________________ b) What is the percent composition by mass of C? Justify your reasoning. 7. Using your answers from question 6, and assuming 100 grams of the unknown compound, convert the percent composition by mass data to the number of moles of each element present in the compound. Show all work to support your answer. 8. Using your answers from question 7, calculate the mole ratios of all elements in the compound. Show all work to support your answers.

4 Model 3: Combustion Analysis Time: 20 minutes Learning objectives: • Correctly analyze data from combustion reactions to produce empirical and molecular formulas. • Practice calculations related to combustion analysis. An unknown compound that contains only carbon and hydrogen (i.e., C X H Y ) reacts with excess oxygen (O 2 ) to produce CO 2 and H 2 O in an elemental analyzer shown below. After completely combusting C X H Y with oxygen in the reaction chamber, the products, CO 2 and H 2 O, flow through the elemental analyzer and are absorbed in separate compartments, as noted in the schematic below. Unreacted O 2 gas flows through both absorbers without changes. The masses of the H 2 O absorber and the CO 2 absorber before and after the combustion of C X H Y are listed in the table below. You may assume all products are fully absorbed. Using this information and your lecture notes, answer the following questions as a group. H 2 O Absorber CO 2 Absorber Mass before combustion of C X H Y 907.1850 g 861.8260 g Mass after combustion of C X H Y 907.2375 g 861.9360 g 11. a) Determine the number of moles of H 2 O that were produced in the combustion of C X H Y . Show all work to support your answer. b) Determine the number of moles of CO 2 that were produced in the combustion of C X H Y . Show all work to support your answer.

5 12. Using your answers from question 11 and your lecture notes, determine the empirical formula of C X H Y . Show all work to support your answer. 13. If the molar mass of C X H Y is 86.177 g/mol, determine the molecular formula of C X H Y . Show all work to justify your reasoning. 14. Using your answers from the questions above, write a balanced chemical reaction for the combustion reaction of C X H Y and O 2 to form CO 2 and H 2 O.