Chapter 11: Problem 117
What is the molar mass of a gas whose density is \(1.52 \mathrm{~g} / \mathrm{L}\) at \(0^{\circ} \mathrm{C}\) and 1 atm pressure?
Short Answer
Expert verified
The molar mass of the gas whose density is \(1.52 \, g / L\) at \(0^{\circ}C\) and \(1 \, atm\) pressure is approximately \(34.04 \, g/mol\).
Step by step solution
01
Convert the given values into appropriate units
Before we proceed, it is necessary to convert the given values into the appropriate units. We must have:
- Temperature in Kelvin (K)
- Pressure in atm (which is already given in the problem)
The temperature conversion from Celsius to Kelvin is given by:
\[T(K) = T(°C) + 273.15\]
\(T(°C) = 0°\)
\[T(K) = 0 + 273.15\]
\[T(K) = 273.15 K\]
Now, we have:
- Temperature: \(T = 273.15 K\)
- Pressure: \(P = 1 atm\)
- Density: \(\rho = 1.52 \, g/L\)
02
Use the Ideal Gas Law equation
The Ideal Gas Law is given by the equation:
\[PV=nRT\]
Where:
- \(P\) is the pressure (atm)
- \(V\) is the volume (L)
- \(n\) is the number of moles
- \(R\) is the ideal gas constant equal to \(0.0821 \, L \cdot atm / (mol \cdot K)\)
- \(T\) is the temperature (K)
We must now rewrite this equation in terms of the given values and the molar mass (also known as the molecular weight, or MW).
Density is defined as mass per unit volume. So, \(\rho = \frac{mass}{volume}\). We can write mass as the product of the molar mass and the number of moles: \(mass = MW \cdot n\). Thus, we can rewrite the density as:
\[\rho = \frac{MW \cdot n}{V}\]
03
Rearrange the Ideal Gas Law to solve for molar mass
Let's substitute the values of pressure, volume, and temperature into the Ideal Gas Law equation and rearrange it to find the molar mass.
Since density is given as \(1.52 \, g/L\), let's consider a volume of \(1 L\) and rearrange the Ideal Gas Law equation in terms of molar mass:
\[PV=nRT\]
\[(MW \cdot n) = \rho \cdot V\]
\[MW = \frac{\rho \cdot V}{n}\]
Now, let's substitute for n using the Ideal Gas Law equation from above: \(n = \frac{PV}{RT}\):
\[MW = \frac{\rho \cdot V}{\frac{PV}{RT}}\]
Simplifying, we get:
\[MW = \frac{\rho \cdot RT}{P}\]
04
Plug in the given values to calculate the molar mass
Now, we can plug in the given values for the density, temperature, and pressure to find the molar mass of the gas:
\[MW = \frac{\rho \cdot RT}{P}\]
\[MW = \frac{(1.52 \, g/L) \cdot (0.0821 \, L \cdot atm \, (mol \cdot K)^{-1}) \cdot (273.15 \, K)}{(1 \, atm)}\]
This simplifies to:
\[MW = \frac{1.52 \times 0.0821 \times 273.15}{1}\]
Calculating the molar mass, we get:
\[MW = \boxed{34.04 \, g/mol}\]
Therefore, the molar mass of the gas whose density is \(1.52 \, g / L\) at \(0^{\circ}C\) and \(1 \, atm\) pressure is approximately \(34.04 \, g/mol\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding the Ideal Gas Law
When exploring the characteristics of gases, the Ideal Gas Law is an essential equation that provides a relationship between pressure, volume, temperature, and the number of moles of the gas. The law is most accurately applied under conditions where gases behave ideally—meaning their particles are infinitely small and don't exhibit intermolecular forces. However, for many practical situations, gases often adhere closely to ideal behavior.
The law is expressed by the equation
\[PV = nRT\],
where P stands for pressure, V is for volume, n represents the number of moles, R is the universal gas constant (\(0.0821 \, L \cdot atm / (mol \cdot K)\)), and T is the temperature in Kelvin. For students tackling gas-related problems, a proper understanding of how to manipulate this equation is pivotal. It allows for the calculation of one variable as long as the others are known.
For more complex calculations, sometimes it's necessary to combine the Ideal Gas Law with other concept equations, such as those for density or molar mass. This flexibility demonstrates the power and utility of the Ideal Gas Law in solving a wide range of gas problems.
The law is expressed by the equation
\[PV = nRT\],
where P stands for pressure, V is for volume, n represents the number of moles, R is the universal gas constant (\(0.0821 \, L \cdot atm / (mol \cdot K)\)), and T is the temperature in Kelvin. For students tackling gas-related problems, a proper understanding of how to manipulate this equation is pivotal. It allows for the calculation of one variable as long as the others are known.
For more complex calculations, sometimes it's necessary to combine the Ideal Gas Law with other concept equations, such as those for density or molar mass. This flexibility demonstrates the power and utility of the Ideal Gas Law in solving a wide range of gas problems.
Calculating Gas Density
Gas density is the mass of gas per unit volume, which has practical implications, from predicting the behavior of weather balloons to understanding the composition of various atmospheres. It can be denoted by the Greek letter rho (\(\rho\)). The equation used to represent density is straightforward:
\[\rho = \frac{mass}{volume}\]
However, when combined with the Ideal Gas Law, it reveals the molar mass of a gas. By considering the density formula and knowing that mass can also be depicted as the product of molar mass and number of moles (mass = MW \(\cdot\) n), we establish a connection to the Ideal Gas Law.
By rearranging the Ideal Gas Law to solve for molar mass, students can find how the density of the gas contributes to determining its molar mass, given temperature and pressure. This is immensely valuable in chemistry for identifying or confirming the identity of an unknown gas by measuring its density under specific conditions.
\[\rho = \frac{mass}{volume}\]
However, when combined with the Ideal Gas Law, it reveals the molar mass of a gas. By considering the density formula and knowing that mass can also be depicted as the product of molar mass and number of moles (mass = MW \(\cdot\) n), we establish a connection to the Ideal Gas Law.
By rearranging the Ideal Gas Law to solve for molar mass, students can find how the density of the gas contributes to determining its molar mass, given temperature and pressure. This is immensely valuable in chemistry for identifying or confirming the identity of an unknown gas by measuring its density under specific conditions.
Understanding Temperature Conversion
Temperature conversion is a fundamental skill when working with gas laws, as equations such as the Ideal Gas Law require temperature to be in Kelvin. Converting from Celsius to Kelvin is a simple matter of adding 273.15 to the Celsius temperature:
\[T(K) = T(°C) + 273.15\].
Students must remember to perform this step to avoid errors in calculations. It's not just a formal requirement; the Kelvin scale is utilized because it is an absolute temperature scale with its zero point at the absolute zero of temperature, where particles theoretically have no thermal motion.
Understanding how to perform temperature conversions is a stepping stone for correctly applying the Ideal Gas Law and other temperature-dependent scientific equations. When solving problems or conducting experiments involving temperature, always ensure the units are consistent throughout the calculation to achieve accurate and meaningful results.
\[T(K) = T(°C) + 273.15\].
Students must remember to perform this step to avoid errors in calculations. It's not just a formal requirement; the Kelvin scale is utilized because it is an absolute temperature scale with its zero point at the absolute zero of temperature, where particles theoretically have no thermal motion.
Understanding how to perform temperature conversions is a stepping stone for correctly applying the Ideal Gas Law and other temperature-dependent scientific equations. When solving problems or conducting experiments involving temperature, always ensure the units are consistent throughout the calculation to achieve accurate and meaningful results.