Pogil The Mole Concept Answer Key

Pogil Activities for the Mole Concept: A Comprehensive Guide with Answers

The mole concept is a cornerstone of chemistry, bridging the macroscopic world of observable quantities to the microscopic world of atoms and molecules. Understanding the mole is crucial for mastering stoichiometry, chemical reactions, and numerous other advanced topics. POGIL (Process-Oriented Guided Inquiry Learning) activities provide a structured, collaborative approach to learning this fundamental concept. This guide offers a comprehensive walkthrough of common POGIL activities focusing on the mole, along with detailed answers and explanations to solidify your understanding.

What is the Mole Concept?

Before delving into the POGIL activities, let's refresh our understanding of the mole. The mole is a unit of measurement in chemistry, representing Avogadro's number (6.022 x 10²³) of particles. These particles can be atoms, molecules, ions, or any other specified entity. This number is incredibly important because it allows us to relate the mass of a substance to the number of particles it contains.

Key Mole-Related Concepts:

• Molar Mass: The mass of one mole of a substance, expressed in grams per mole (g/mol). It's numerically equal to the atomic or molecular weight of the substance.
• Avogadro's Number: The number of particles (atoms, molecules, ions, etc.) in one mole of a substance.
• Conversion Factors: Using molar mass and Avogadro's number to convert between mass, moles, and the number of particles.
• Empirical and Molecular Formulas: Determining the simplest whole-number ratio of atoms in a compound (empirical formula) and the actual number of atoms of each element in a molecule (molecular formula).

Common POGIL Activities and Solutions (Illustrative Examples):

While specific POGIL activities vary, the core concepts remain consistent. We will illustrate with example problems and solutions that mirror the structure and thought process of typical POGIL exercises.

Activity 1: Calculating Molar Mass

Problem: Calculate the molar mass of water (H₂O). The atomic mass of hydrogen (H) is approximately 1.01 g/mol, and the atomic mass of oxygen (O) is approximately 16.00 g/mol.

Solution:

1. Identify the elements and their atomic masses: Water contains two hydrogen atoms and one oxygen atom.
2. Calculate the contribution of each element: Two hydrogen atoms contribute 2 * 1.01 g/mol = 2.02 g/mol. One oxygen atom contributes 16.00 g/mol.
3. Add the contributions: The molar mass of water is 2.02 g/mol + 16.00 g/mol = 18.02 g/mol.

Activity 2: Converting Grams to Moles

Problem: How many moles are present in 10.0 grams of carbon dioxide (CO₂)? The molar mass of carbon dioxide is approximately 44.01 g/mol.

Solution:

1. Write down the given information: We have 10.0 grams of CO₂, and the molar mass of CO₂ is 44.01 g/mol.
2. Set up the conversion factor: We'll use the molar mass as a conversion factor: (1 mol CO₂ / 44.01 g CO₂)
3. Perform the calculation: (10.0 g CO₂) * (1 mol CO₂ / 44.01 g CO₂) = 0.227 moles CO₂

Activity 3: Converting Moles to Number of Particles

Problem: How many molecules of carbon dioxide (CO₂) are present in 0.227 moles of CO₂?

Solution:

1. Write down the given information: We have 0.227 moles of CO₂.
2. Use Avogadro's number as the conversion factor: (6.022 x 10²³ molecules CO₂ / 1 mol CO₂)
3. Perform the calculation: (0.227 mol CO₂) * (6.022 x 10²³ molecules CO₂ / 1 mol CO₂) = 1.37 x 10²³ molecules CO₂

Activity 4: Determining Empirical and Molecular Formulas

Problem: A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Its molar mass is determined to be 180 g/mol. Determine the empirical and molecular formulas.

Solution:

1. Assume a 100g sample: This simplifies calculations. We have 40.0 g C, 6.7 g H, and 53.3 g O.
2. Convert grams to moles: Use atomic masses (C = 12.01 g/mol, H = 1.01 g/mol, O = 16.00 g/mol) to convert grams to moles for each element.
   • Moles of C = 40.0 g / 12.01 g/mol ≈ 3.33 mol
   • Moles of H = 6.7 g / 1.01 g/mol ≈ 6.63 mol
   • Moles of O = 53.3 g / 16.00 g/mol ≈ 3.33 mol
3. Determine the mole ratio: Divide each mole value by the smallest number of moles (3.33 mol):
   • C: 3.33 mol / 3.33 mol = 1
   • H: 6.63 mol / 3.33 mol ≈ 2
   • O: 3.33 mol / 3.33 mol = 1
4. Write the empirical formula: The empirical formula is CH₂O.
5. Determine the molecular formula: Find the molar mass of the empirical formula (CH₂O): 12.01 + 2(1.01) + 16.00 = 30.03 g/mol.
6. Calculate the ratio: Divide the given molar mass (180 g/mol) by the empirical formula molar mass (30.03 g/mol): 180 g/mol / 30.03 g/mol ≈ 6.
7. Write the molecular formula: Multiply the subscripts in the empirical formula by 6: (C₆H₁₂O₆)

Activity 5: Stoichiometry and Mole Ratios

Problem: Consider the balanced chemical equation: 2H₂(g) + O₂(g) → 2H₂O(l). If you react 4.0 moles of hydrogen gas (H₂) with excess oxygen gas (O₂), how many moles of water (H₂O) will be produced?

Solution:

1. Identify the mole ratio: The balanced equation shows that 2 moles of H₂ react to produce 2 moles of H₂O. This gives a mole ratio of 1:1.
2. Use the mole ratio as a conversion factor: (2 mol H₂O / 2 mol H₂)
3. Perform the calculation: (4.0 mol H₂) * (2 mol H₂O / 2 mol H₂) = 4.0 moles H₂O

Activity 6: Limiting Reactant

Problem: Consider the reaction: N₂(g) + 3H₂(g) → 2NH₃(g). If you react 2.0 moles of N₂ with 6.0 moles of H₂, which is the limiting reactant, and how many moles of NH₃ are produced?

Solution:

1. Determine the mole ratio: From the balanced equation, the mole ratio of N₂ to H₂ is 1:3.
2. Compare mole ratios: We have a 2:6 mole ratio of N₂ to H₂, which simplifies to 1:3. This matches the stoichiometric ratio, indicating neither reactant is in excess. Both reactants are completely consumed.
3. Calculate moles of NH3: Using the mole ratio from the balanced equation (1 mol N₂ produces 2 mol NH₃): (2.0 mol N₂) * (2 mol NH₃ / 1 mol N₂) = 4.0 moles NH₃

These examples illustrate the typical problem-solving approach within POGIL activities related to the mole concept. Remember that successful completion hinges on a solid understanding of the definitions and relationships between mass, moles, and the number of particles. Thorough practice with diverse problems will enhance your mastery of this critical area of chemistry. Remember to always double-check your calculations and units to avoid errors. The key is to break down complex problems into smaller, manageable steps, using dimensional analysis to ensure proper cancellation of units. With consistent effort and practice, you'll confidently navigate the intricacies of the mole concept and its applications in chemistry.