Ch.3 - Mass Relationships in Chemical Reactions

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.3 - Mass Relationships in Chemical Reactions

Problem 97

Chapter 3, Problem 97

Nitrogen fixation in the root nodules of peas and other leguminous plants is carried out by the molybdenum-containing enzyme nitrogenase. What is the molecular mass of nitrogenase if the enzyme contains two molybdenum atoms and is 0.0872% Mo by mass?

Verified step by step guidance

Step 1: Understand the problem. We need to find the molecular mass of nitrogenase, given that it contains two molybdenum (Mo) atoms and is 0.0872% Mo by mass.

Step 2: Determine the molar mass of molybdenum (Mo). The atomic mass of Mo is approximately 95.95 g/mol.

Step 3: Calculate the total mass of molybdenum in one molecule of nitrogenase. Since there are two Mo atoms, multiply the atomic mass of Mo by 2.

Step 4: Use the percentage by mass formula to set up an equation. The formula is: (mass of Mo in nitrogenase / molecular mass of nitrogenase) * 100 = 0.0872.

Step 5: Solve the equation for the molecular mass of nitrogenase. Rearrange the equation to find the molecular mass of nitrogenase.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Mass

Molecular mass is the mass of a molecule calculated as the sum of the atomic masses of all the atoms in its molecular formula. It is typically expressed in atomic mass units (amu) or grams per mole (g/mol). Understanding how to calculate molecular mass is essential for determining the composition and properties of compounds, including enzymes like nitrogenase.

Percent Composition

Percent composition refers to the percentage by mass of each element in a compound. It is calculated by dividing the mass of the element in the compound by the total mass of the compound and multiplying by 100. In this question, knowing that nitrogenase is 0.0872% molybdenum by mass allows us to relate the mass of molybdenum to the total mass of the enzyme.

Enzyme Structure and Function

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are typically proteins that may contain metal ions, such as molybdenum in nitrogenase, which are crucial for their catalytic activity. Understanding the role of metal ions in enzyme function is important for grasping how nitrogenase facilitates nitrogen fixation in plants.

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