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Ch.10 - Gases: Their Properties & Behavior
Chapter 10, Problem 67

What is the density in g/L of a gas mixture that contains 27.0% F2 and 73.0% He by volume at 714 mm Hg and 27.5 °C?

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1
Convert the temperature from Celsius to Kelvin by using the formula: T(K) = T(°C) + 273.15.
Use the ideal gas law equation, PV = nRT, to find the total number of moles of the gas mixture. Rearrange the equation to solve for n (number of moles): n = \frac{PV}{RT}.
Calculate the partial pressures of F2 and He using their volume percentages and the total pressure. For each gas, use the formula: P_{gas} = \frac{percentage}{100} \times total\_pressure.
Using the ideal gas law again, calculate the number of moles for each gas separately using their partial pressures. For each gas, use n_{gas} = \frac{P_{gas}V}{RT}.
Find the total mass of the gas mixture by adding the masses of F2 and He, calculated from their moles and molar masses. Then, calculate the density of the gas mixture using the formula: density = \frac{total\_mass}{volume}.

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Key Concepts

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

Density of Gases

Density is defined as mass per unit volume. For gases, density can be expressed in grams per liter (g/L). The density of a gas can be calculated using the ideal gas law, which relates pressure, volume, temperature, and the number of moles of gas. Understanding how to manipulate this relationship is crucial for solving density-related problems.
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Partial Pressure and Dalton's Law

Dalton's Law states that in a mixture of gases, the total pressure is equal to the sum of the partial pressures of each individual gas. The partial pressure of a gas can be calculated by multiplying its mole fraction by the total pressure. This concept is essential for determining the contribution of each gas in a mixture to the overall density.
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Ideal Gas Law

The Ideal Gas Law is a fundamental equation in chemistry, expressed as PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature in Kelvin. This law allows for the calculation of various properties of gases, including density, by rearranging the equation to solve for the desired variable. It is particularly useful in problems involving gas mixtures.
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