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Ch.8 Gases, Liquids and Solids
McMurry - Fundamentals of GOB 8th Edition
McMurry8th EditionFundamentals of GOBISBN: 9780134015187Not the one you use?Change textbook
Chapter 8, Problem 20

Determine the percent composition of air in the lungs from the following composition in partial pressures: PN2= 573 mmHg, PO2 = 100 mmHg, PCO2 = 40 mmHg, and PH2O = 47 mmHg; all at 37 °C and 1 atm pressure.

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1
Step 1: Understand the concept of percent composition. Percent composition is calculated as the ratio of the partial pressure of a specific gas to the total pressure, multiplied by 100 to express it as a percentage.
Step 2: Calculate the total pressure in the lungs by summing up the partial pressures of all the gases: PN2, PO2, PCO2, and PH2O. Use the formula: Ptotal = PN2 + PO2 + PCO2 + PH2O.
Step 3: For each gas, calculate its percent composition using the formula: %composition = (Pgas / Ptotal) × 100. Substitute the partial pressure of each gas and the total pressure into this formula.
Step 4: Perform the calculation for each gas: nitrogen (N2), oxygen (O2), carbon dioxide (CO2), and water vapor (H2O). Ensure that the units of pressure are consistent throughout the calculation.
Step 5: Summarize the percent composition of each gas in the lungs. Verify that the sum of all percentages is approximately 100%, accounting for rounding errors.

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Key Concepts

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

Partial Pressure

Partial pressure refers to the pressure exerted by a single gas in a mixture of gases. It is a crucial concept in understanding gas behavior in the lungs, as each gas contributes to the total pressure of the mixture. In this context, the partial pressures of nitrogen, oxygen, carbon dioxide, and water vapor are used to determine their respective contributions to the overall composition of air in the lungs.
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Percent Composition

Percent composition is a way to express the concentration of a component in a mixture as a percentage of the total. In the context of gases in the lungs, it is calculated by dividing the partial pressure of each gas by the total pressure and multiplying by 100. This allows for a clear understanding of how much of each gas is present relative to the total pressure of the air mixture.
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Total Pressure

Total pressure is the sum of the partial pressures of all gases in a mixture. In this scenario, the total pressure is given as 1 atm, which is equivalent to 760 mmHg. To find the percent composition of air in the lungs, one must first calculate the total pressure from the provided partial pressures and then use this value to determine the individual gas contributions.
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