MIT CCCT - 03 Water vapor capacity of air

Experiment: How temperature affects the water vapor capacity of air

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

Time: 30 minutes

Level: Intermediate

Materials:

3 glass jars with lids, about 16 oz or 500 ml
2 glass bowls, such as 4 cup Pyrex bowls
3 digital hygrometers
clear tape, like scotch transparent tape
Electric kettle or other device to heat water
Ice cubes
vapor pressure diagram (link or pdf) and data sheet

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

Science references

How to estimate the water moisture content of humid air from temperature and relative humidity by interpolating from a chart: www.conservationphysics.org/atmcalc/vp_diag.pdf linked from www.conservationphysics.org/atmcalc/atmoclc1.html

How to estimate the water moisture content of humid air from temperature and relative humidity, using an online calculator: https://www.quadco.engineering/en/know-how/cfd-calculate-water-fraction-humid-air.htm

Procedure

Step 1

Tape the hygrometers into the jars, facing out, near the top.

Mark one jar as hot and one as cold

Leave the jars open and wait a few minutes until the temperatures stabilize and the hygrometers show similar values. (Should be within a range of +/- 2 °F and +/-2 % RH.)

Seal the jars by twisting the lids on securely.

Step 2

Prepare boiling water (use the electric kettle) and ice water.

Place the jars in the glass bowls and carefully pour the boiling water and ice water in the bowls, around the jars, until mostly full.

Step 3

Watch the readings on the hygrometers. When they stabilize (about 5 minutes) record the temperature and relative humidity values on the worksheet. Convert the temperature values from °F to °C using an online converter or this equation: °C = (°F - 32) x 5 / 9

Water vapor worksheet.pdf

Step 4

Follow the instructions on the worksheet and use the vapor pressure diagram to estimate the saturation concentration of water vapor for each jar. Another way to say this is find out how much water can evaporate into air of that temperature, without condensing into droplets.

Record your observations (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.