Explain how a gas is collected over water. Why does the temperature of the gas need to be known

Explain how a gas is collected over water. Why does the...

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Key Concepts

Gas Collection Over Water

This method involves capturing a gas by displacing water, typically in an inverted container. As the gas is produced, it fills the container and pushes out water, meaning the collected gas inevitably contains water vapor alongside the target gas.

Dalton's Law of Partial Pressures

According to Dalton's law, the total pressure inside a collection container is the sum of the partial pressures of all gases present. When a gas is collected over water, the measured pressure is the combined pressure of the desired gas and the water vapor, making it necessary to separate the contributions to determine the actual gas pressure.

Vapor Pressure and Temperature

Water has a vapor pressure that increases with temperature, which means that the amount of water vapor present in the collected gas depends on the temperature of the system. Knowing the temperature is essential to accurately determine the vapor pressure of water, so that its contribution can be subtracted from the total pressure, yielding the pressure of the collected gas alone.

Transcript

00:02 All right, problem 19 wants to know how to, or wants us to explain how a gas can be collected over water.

00:10 So we need some sort of glass container.

00:14 I am going to use a graduated cylinder.

00:19 I'm going to take that graduated cylinder and fill it completely full of water and turn it upside down.

00:31 So we have a graduated cylinder completely filled with water and it's turned upside down.

00:42 We are going to conduct our reaction in some sort of container.

00:47 I guess i'll put it into a little erlmeier flask here.

00:53 That is sealed with a rubber tube rubber stopper, but there is a tube going through the rubber stopper.

01:02 And that tube is attached to some flexible tubing, where we stick the open end of the flexible tubing under the surface of our water.

01:16 All right, so as this reaction starts taking place, starts producing gas, the gas is going to travel through the tube, and then because it is less dense than the water, it's going to start bubbling up and collecting in the graduated cylinder.

01:35 It's going to displace the water.

01:37 Some of the water will be removed out the bottom, and we end up with our gas sample trapped in this inverted tube.

01:49 A better drawing there.

01:52 Or in the inverted tube of the inverted tube of the the graduate cylinder that i'm using here...

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