High School

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. [tex]\( 93.9 \, \text{kPa} \)[/tex]

B. [tex]\( 98.1 \, \text{kPa} \)[/tex]

C. [tex]\( 100.3 \, \text{kPa} \)[/tex]

D. [tex]\( 104.5 \, \text{kPa} \)[/tex]

Answer :

To find the partial pressure of hydrogen in the collecting bottle, you can follow these steps:

1. Understand the Problem:
When you collect hydrogen gas over water, you get a mixture of hydrogen gas and water vapor. The total pressure measured in the bottle is a combination of both the hydrogen gas pressure and the water vapor pressure.

2. Use the Total Pressure Value:
The total pressure in the collecting bottle is given as 97.1 kilopascals (kPa).

3. Use the Water Vapor Pressure:
The vapor pressure of the water in the collecting bottle is given as 3.2 kilopascals (kPa).

4. Apply Dalton’s Law of Partial Pressures:
Dalton’s Law states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases. In this case:
[tex]\[
\text{Total Pressure} = \text{Partial Pressure of Hydrogen} + \text{Water Vapor Pressure}
\][/tex]

5. Calculate the Partial Pressure of Hydrogen:
You need to rearrange the equation to solve for the partial pressure of hydrogen:
[tex]\[
\text{Partial Pressure of Hydrogen} = \text{Total Pressure} - \text{Water Vapor Pressure}
\][/tex]
Substitute the known values into the equation:
[tex]\[
\text{Partial Pressure of Hydrogen} = 97.1\, \text{kPa} - 3.2\, \text{kPa} = 93.9\, \text{kPa}
\][/tex]

So, the partial pressure of the hydrogen gas is 93.9 kPa. The correct answer is A. 93.9 kPa.