Investigating evaporation

Students will investigate evaporation as a cooling process. They will witness that temperature is affected by moisture content and the process of evaporation. Next, they will explore websites related to the processes of evaporation and condensation. Students will apply gained knowledge to real-life situations, and will share their new knowledge with a person outside the classroom.

A lesson plan for grade 7 Science

By Jessica Bohn

Learn more

• Dew Point information on what the dew point is, with links to other weather topics
• NBC Weather information about humidity and the dew point
• The Atmosphere I, a lecture by C. Lithgow-Bertelloni Go about 3/4 down the page to the part about Temperature Variations and Phase Changes

Related pages

• The effects of acid rain on the environment: This is an experiment in which groups of students are given healthy plants to water with different solutions of an acid rain mixture made in class. Students will document and present their findings. This lesson plan has modifications for an Intermediate Low English Language Learner (ESL student).
• State Climate Office of North Carolina: Students of all ages will enjoy learning about North Carolina's climate, whether on a field trip or in their classroom. Topics include extreme weather records, drought, tornadoes, El Nino and La Nina, hurricanes and North Carolina, and much more.
• Colburn Earth Science Museum: The best rock and mineral specimens from the Burnham Standish Colburn collection are housed in the Colburn Earth Science Museum. Students will enjoy the programs that are centered around this collection of fossils, gems, and North Carolina minerals.

Related topics

• Learn more about atmosphere, dew point, earth science, evaporation, humidity, and science.

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Learning outcomes

Goals:

• Students will understand that evaporation, while endothermic, is a cooling process.
• Students will use technology to enhance learning.

Objectives:

• Students will examine temperature changes resulting from the application of evaporation.
• Students will explain evaporation and apply knowledge to concept of cloud formation.

Teacher planning

Time required for lesson

100 minutes

Materials/resources

Materials for each group of students:

• provided assessments
• provided chart
• pens or pencils (three colors)
• one shoelace with plastic tips cut off
• one box cutter or scissors
• three thermometers
• one plastic bottle
• one roll of clear tape
• one timer
• two cups of room-temperature water
• one piece of graph paper

For each student:

• copy of “Application of Learned Concepts”

Technology resources

• a computer with internet access for each pair of students

Pre-activities

Students should be familiar with lab procedures, general safety rules and how to navigate the internet using the computers that are available to the class. Basic computer and internet tips may have to be covered in a prior class.

Students should know how to construct a line graph. Teacher may use a workgroup or paired activity to allow students to review with each other.

Content Knowledge:

Students should have an understanding of humidity and dew point before beginning the lesson.

These are some focus question which should be discussed with the class:

• What is the relative humidity when the dew point is reached?
• Which process, evaporation or condensation, adds moisture to the air?
• Which process, evaporation or condensation, subtracts moisture from the air?
• Does the temperature of the air affect the rate of evaporation?

Students should be asked how evaporation affects their life. These ideas should be documented on the board or on transparency for later reference.

Pre-lab preparation:

Allow 2–3 cups of water to sit at room temperature over night. This will allow the water to adjust to the same temperature as the air. Explain to the students why you would want to do this (to eliminate uncontrolled variables).

Activities

Verbally explain the procedure to all students and have a transparency ready with pictures or written words for visual learners.

Explain the following Operational Definitions (as some students may not be able to deduce these items):

• Wet-bulb: the thermometer with the wet shoelace wrapped around it.
• Dry-bulb: the thermometer on the outside of the container without a wet shoelace wrapped around it.
• Control bulb: the thermometer submerged in the water.

Define the variables (Draw upon prior knowledge of the scientific method when doing this.):

• Independent Variable: the exposure to evaporation.
• Dependent Variable: the temperature of the air.
• Controlled Variables: same type of thermometers, same water for control bulb and wet-bulb, same starting temperature on all thermometers.
• Uncontrolled Variables: Anything unaccounted for, such as bottle temperature influence on water

Setup Procedures: (twenty minutes)

1. Gather materials and assign the following jobs: timer, recorder, and thermometer-reader. (Each student should have a job when doing cooperative activities. A supplies/clean up person can be added for groups of four.)
2. Use the scissors or other cutting utensil to cut a hole about the size of a nickel mid-way across the side of the bottle.
3. Fill the bottle with the room temperature water to just below the hole on the side of the bottle.
4. Place one of the thermometers inside the bottle, so that the bulb sits under water. This is the control bulb.
5. Place a second thermometer on the outside of the bottle by using clear tape to secure it to the side of the bottle. Secure it to the side of the bottle opposite the hole. No water should be touching this thermometer, the dry-bulb.
6. Use clear tape to secure the third thermometer to the outside of the bottle, next to the hole.
7. Place the shoelace in the water inside of the bottle, so that the entire length of the shoelace is wet. Then, feed one end of the shoelace through the hole, to the outside of the bottle.
8. Wrap the shoelace around the bulb of the thermometer that is located right next to the hole. The other end of the shoelace should remain in the water, inside of the bottle. This third thermometer is the wet-bulb thermometer.

Recording Data: (twenty minutes) (Teacher should assess what students think will happen while they are timing and recording.)

1. Record the temperature of each thermometer for time 0:00 in the chart.
2. Record the temperature of each thermometer in the chart every two minutes thereafter.
3. During this phase, remind students that the ultimate objective (NC SCOS) is to analyze weather systems, with regard to humidity and cloud formation, and that this activity provides the foundation for doing so.
4. Clean Up and perform “Assessment of Results” as homework or classwork (can be the end of class one, if working on fifty-five minute classes)

Post-Lab Activities (20–25 minutes) (can be the next day if working on fifty-five minute classes):

• Each group of students should make a line graph of the temperature reading for each thermometer over the twenty minute period. Students within groups discuss results, trends and conclusions, and document those at the bottom of the group graph.

Technology Component (20–25 minutes):

Students will use computers to access the internet to gain more information about evaporation, condensation and how this relates to the whole picture of the hydrologic cycle.

1. Access information on humidity and dewpoint and use the information to answer the questions provided in the “Web Investigations Assessment” on evaporation and condensation.
2. Students should also click on the links for the water cycle and clouds to relate this information to future learning.

Individual Practice:

• Assign “Application of Learned Concepts” for homework (or classwork) assessment. This should be done individually. In conjunction with this, the student should explain what he/she did and what was learned to an adult outside the classroom, obtaining his/her signature at the bottom of the form.

Closure:

• Go back to the class list about how evaporation affects every-day life. Students should be able to edit and add a few things. If not, some teacher reflection and modification may be needed.

Assessment

• Teacher Observation—Teacher should check to see that students understand the directions and work through each segment of the lesson together.
• Assessment of Results to be completed after recording data and can be assigned as homework for those on a traditional 50–55 minute schedule.
• Graph of temperature trends with all three thermometer readings on the same graph (sample graph). This was completed as a group assignment.
• Web Investigation Assessment to be completed while doing Technology Component in order to assess content knowledge.
• Application of Learned Concepts to be completed at end of lesson. The purpose of this is to use higher order thinking skills to apply learned concepts to real-life situations. The second component of this is an authentic assessment that involves the student conferencing with a parent or another teacher and explaining what was learned, getting their signature, date and telephone number as evidence.

Supplemental information

• Application of Learned Concepts
• Assessment of Results
• Chart for Recording Results
• Web Investigations Questions
• Example Graph
• Explanatory Pictures

Comments

An extension on the investigation portion of this lesson would be to have students fan the wet and dry bulb thermometers at the end of their twenty minute recording session. This will show more dramatic results. Question them about why these results happen.