03 Water vapor capacity of air

Experiment: How temperature affects the water vapor capacity of air

Compare the amount of water vapor in air over water of various temperatures.

Time: 30 minutes

Level: Intermediate

Materials:

4 glass jars, about 24 oz or 750 ml
Thermometer, analog or digital. Ideally 1 for each jar.
Electric kettle or other device to heat water
Ice cubes
Plastic sheet to cover jars. Do not use “Saran” wrap as it will stretch under the ice. Snack bags cut apart will work well.
Rubber bands

Specifics and purchasing links are on this spreadsheet Materials list for CCSAE experiments

Procedure

Step 1

Start the investigation by filling 4 jars with water at these temperatures:

Ice water
Room temperature
Hot tap water
Boiling water

Wait a few minutes until each jars is at the same temperature as the water in it. Do this by holding temperature probes in the middle of the water until the reading stabilizes, then adding cold or hot water to achieve the desired temperatures.

Step 2

Pour out most of the water, leave ~ ¼ in, cover with a plastic sheet and seal with your hand

Step 3

Invert the jar and pour out the water, keeping the water vapor in the jar.

Use mitts when draining the boiling water.

Step 4

Place a few ice cubes on top of each jar

Step 5

After 5 minutes, remove the ice, dry the tops and observe the water condensed on the plastic.

Tap the tops as needed to get the drops to collect.

Step 6

If there is not much condensation, repeat steps 4 and 5

Step 7

Remove the ice, dry the tops and observe the water condensed on the plastic sheet:

Draw your own conclusion (open the box below to see our suggestions)

Suggestions:

The air from the warmest jar held the most moisture.

There was more water vapor in the warmer jars than in the cooler jars.

Do a similar investigation where some water is left in the jars (#11).

This should also show more condensation in the warmer jars, however, that water vapor is coming from the water still in the jar as well as the vapor.

Identify the physical, chemical or biological mechanism that is happening (open this box after you have an idea)

The mechanism is Water vapor capacity of air

The most condensation was on the jar with the warmest water, so it held the most water vapor.

The least condensation was on the jar with the ice water, so it held the least water vapor.

Warmer air can hold more moisture (water vapor) than cooler air.

Relate this mechanism to climate change

Find the arrow (→) in the framework that represents this mechanism (starts at the cause phenomenon and goes to the effect phenomenon). (Use your printed copy of the framework, or open the one here. )

Pathway for Extreme and Changing Weather.pdf

Open this box to check your connection.

Then go to the Explainer pages to learn more about the Cause and Effect phenomena

Connection 3

Cause: Warmer air

What is happening: warm air can hold more water vapor

Effect: More water vapor in the air

Warmer climates will cause more water vapor to be present in the air, and since water vapor is a greenhouse gas, they will contribute to even more warming on the planet.

A lot of water vapor is available over the ocean, as compared to a dry place like a desert. Warm air above the ocean will hold more of that water vapor than cold air above the ocean would hold.

We’d love to hear how you used this tool in your community, how the students responded, and your suggestions to improve the experiments and other resources. Contact us at ccsae@mit.edu.