Gas Laws Fact Sheet

[tex]
\[
\begin{array}{|l|l|}
\hline
\text{Ideal gas law} & PV = nRT \\
\hline
\text{Ideal gas constant} & R = 8.314 \left[\frac{L \cdot kPa}{mol \cdot K}\right] \\
\hline
& \text{or } R = 0.0821 \frac{L \cdot atm}{mol \cdot K} \\
\hline
\end{array}
\]
[/tex]

Select the correct answer.

When a chemist collects hydrogen gas over water, she ends up with a mixture of hydrogen and water vapor in her collecting bottle. If the pressure in the collecting bottle is 97.1 kilopascals and the vapor pressure of the water is 3.2 kilopascals, what is the partial pressure of the hydrogen?

A. 93.9 kPa
B. 98.1 kPa
C. 100.3 kPa
D. 104.5 kPa

To find the partial pressure of hydrogen gas when it's collected over water, we use Dalton's Law of Partial Pressures. This law states that the total pressure in a gas mixture is the sum of the partial pressures of the individual gases.

Here's how you can solve the problem step-by-step:

1. Identify the Total Pressure: The total pressure in the collecting bottle is given as 97.1 kilopascals (kPa).

2. Identify the Vapor Pressure of Water: The vapor pressure of the water is given as 3.2 kilopascals (kPa).

3. Calculate the Partial Pressure of Hydrogen: According to Dalton's Law, the partial pressure of the hydrogen gas is calculated by subtracting the vapor pressure of the water from the total pressure.

[tex]\[
\text{Partial Pressure of Hydrogen} = \text{Total Pressure} - \text{Vapor Pressure of Water}
= 97.1 \, \text{kPa} - 3.2 \, \text{kPa} = 93.9 \, \text{kPa}
\][/tex]

Therefore, the partial pressure of the hydrogen gas is 93.9 kPa.

So, the correct answer is:
A. 93.9 kPa