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Ch.10 - Gases
Chapter 10, Problem 51a

(a) Calculate the density of NO2 gas at 0.970 atm and 35 °C.

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Step 1: First, we need to convert the temperature from Celsius to Kelvin. The formula to convert Celsius to Kelvin is K = °C + 273.15.
Step 2: Next, we will use the ideal gas law equation, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature. However, we need to rearrange the equation to solve for the density (d) of the gas. The density of a gas is its mass (m) divided by its volume (V), and the mass of a gas is the number of moles (n) times the molar mass (M). So, we can substitute m/V for d and nM for m in the ideal gas law equation to get d = PM/RT.
Step 3: Now, we can plug in the given values into the rearranged ideal gas law equation. The pressure (P) is 0.970 atm, the molar mass (M) of NO2 is 46.01 g/mol (which you can find by adding up the atomic masses of nitrogen and oxygen), the ideal gas constant (R) is 0.0821 L·atm/K·mol (since the pressure is given in atm), and the temperature (T) is the value we calculated in step 1.
Step 4: After plugging in the values, we can solve the equation to find the density of NO2 gas at the given conditions.
Step 5: The final step is to check the units of your answer. The density should be in g/L, which is the mass of the gas divided by the volume it occupies.

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Key Concepts

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

Ideal Gas Law

The Ideal Gas Law relates the pressure, volume, temperature, and number of moles of a gas through the equation PV = nRT. This law is essential for calculating properties of gases under various conditions, including density. By rearranging the equation, density can be expressed as d = PM/RT, where d is density, P is pressure, M is molar mass, R is the ideal gas constant, and T is temperature in Kelvin.
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Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For nitrogen dioxide (NO2), the molar mass is calculated by summing the atomic masses of nitrogen (N) and oxygen (O) in the molecule. Understanding molar mass is crucial for converting between mass and moles, which is necessary for applying the Ideal Gas Law to find density.
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Gas Density

Gas density is defined as the mass of gas per unit volume, usually expressed in grams per liter (g/L). It can be influenced by factors such as temperature and pressure. In the context of the Ideal Gas Law, density can be calculated using the rearranged formula, allowing for the determination of how much mass of a gas occupies a specific volume under given conditions.
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Related Practice
Textbook Question
Rank the following gases from least dense to most dense at 101.33 kPa and 298 K: O2, Ar, NH3, HCl.
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Textbook Question
Rank the following gases and vapors from least dense to most dense at 101.33 kPa and 298 K: water vapor 1H2O1g22, nitrogen 1N22, hydrogen sulfide 1H2S2.
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Textbook Question

Which of the following statements best explains why a closed balloon filled with helium gas rises in air? (a) Helium is a monatomic gas, whereas nearly all the molecules that make up air, such as nitrogen and oxygen, are diatomic. (b) The average speed of helium atoms is greater than the average speed of air molecules, and the greater speed of collisions with the balloon walls propels the balloon upward. (c) Because the helium atoms are of lower mass than the average air molecule, the helium gas is less dense than air. The mass of the balloon is thus less than the mass of the air displaced by its volume. (d) Because helium has a lower molar mass than the average air molecule, the helium atoms are in faster motion. This means that the temperature of the helium is greater than the air temperature. Hot gases tend to rise.

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Textbook Question

(b) Calculate the molar mass of a gas if 2.50 g occupies 0.875 L at 685 torr and 35 °C

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Textbook Question
(b) Calculate the molar mass of a vapor that has a density of 7.135 g>L at 12 °C and 99.06 kPa.
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Textbook Question
In the Dumas-bulb technique for determining the molar mass of an unknown liquid, you vaporize the sample of a liquid that boils below 100 °C in a boiling-water bath and determine the mass of vapor required to fill the bulb. From the following data, calculate the molar mass of the unknown liquid: mass of unknown vapor, 1.012 g; volume of bulb, 354 cm3; pressure, 98.93 kPa; temperature, 99 °C.
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