## Evaporation Marathon

### Cheryle BorsosSanta Rosa District Schools

#### Description

Runners take your mark! This lesson involves a student experiment to see which container evaporates water the quickest. The lesson invites students to explore independent and dependent variables as part of the experimentation process.

#### Objectives

The student knows how to identify the independent and dependent variables in an experiment.

The student uses appropriate experimental design, with consideration for rules, time, and materials required to solve a problem.

#### Materials

-Class set of Evaporation Marathon Lab Investigation sheets (See Associated File)
-One 100mL graduated cylinder for each lab station (8)
-One 9-inch pie tin for each lab station (8)
-One 500mL beaker for each lab station (8) (Glass jars can be used as a substitute.)
-Water source
-Funnel

#### Preparations

1. Gather materials and set up 8 lab stations around the room.
2. Duplicate the Evaporation Marathon Lab Investigation sheets for each student. (See Associated File)

#### Procedures

DAY ONE
1. Activate student interest by telling the students that they are going to participate in a marathon! Ask the students if they know how far a runner must run in a marathon. (26.2 miles) Then reassure them that they are not actually going to be running 26.2 miles in today’s lesson, but that they are going to do an experiment that is called “Evaporation Marathon.” Invite students to make an inference about what an evaporation marathon might involve. Then tell them that they will be investigating which type of container is the fastest “runner” in the evaporation marathon.

2. At this point, review the steps of the scientific method with the class. Remind students that scientists use a series of planned steps to solve a problem. The steps they use are called the scientific method. A commonly used method involves five steps. First, identify the problem. Second, make a hypothesis. Third, test the hypothesis by doing an experiment. Fourth, analyze the results of the experiment. Fifth, draw a conclusion.

3. After this brief review, key in on the experimental phase of the scientific method. Explain that every experiment has a constant and variables. Define variables as “a changeable factor in an experiment.” Define a constant as “the factor that remains the same throughout the experiment.” Then elaborate on the two types of variables in an experiment, the independent variable and the dependent variable.

4. Ask students if they know the meaning of the word independent. (Not dependent on another)

5. Then ask them if they know the meaning of the word dependent. (Relies on another)

6. Explain that the independent variable is the variable that the scientist has direct control over and can change, while the dependent variable is influenced by the independent variable. The dependent variable is the thing being measured in an experiment.

7. Provide the students with some examples of this concept. Begin by using an example to which they can relate. For example, ask the students to suppose they were going to make \$5.00 an hour to walk the neighbor’s dog. The number of hours they work results in the amount of money they will earn. Explain that the independent variable is the one that they control, the number of hours they walk the dog. The dependent variable, which is the amount of money they will earn, depends on the amount of hours they walk the dog. Restate that the amount of money earned depends on the amount of time worked. Therefore, the dependent variable is the amount of money earned. The independent variable is the amount of time worked.

8. For the second example, use a scientific scenario. Ask the students to think about an experiment in which they were going to determine the amount of time it takes water to reach boiling (100 degrees Celsius), using a hotplate. Tell them that the temperature of the water would be recorded every two minutes. Ask students to identify the independent variable (time) and the dependent variable (temperature). Help them see that the experimenter controlled the time. The time variable could be changed to every one-minute or every five minutes, etc. This is the independent variable. The dependent variable, temperature, depends on the amount of time that the water is on the hotplate. The temperature is the variable being measured.

9. Explain to the students that they are going to be doing an experiment where they will use the scientific method to solve a problem. They will need to identify the dependent and the independent variable used in the experiment.

10. Review expected behaviors of cooperative workers as the students work in lab groups. Hand out the Evaporation Marathon Lab Investigation sheets (See Associated File) to each student. You may wish to read the lab aloud with the students before they move to their lab stations.

11. During the reading of the lab, explain and review the concepts in the background information section of the lab sheet pertaining to boiling and evaporation. This is a clear and easy introduction if your students have not had a lesson on this. It is also a great way to review the phase change from a liquid to a gas through evaporation and boiling.

12. Once students have read through the lab and made a hypothesis, invite them to move to their lab stations to set up the experiment. Note: This lab requires students to observe data over a three-day period, so they will not have finished the data collection or conclusion at this point in the investigation.

13. As students are working in their lab groups, circulate to each group to answer questions and ask students to share why they chose a particular hypothesis. This is also a good time for the teacher to complete the cooperative worker section on the Goal 3 Standards Checklist. (See Associated File)

14. After students have set up the lab, invite them back to their seats to share their hypothesis by asking them which container they think is going to win the evaporation marathon. Remind them not to change their hypothesis based on others' ideas. A hypothesis is something they are testing. There is no correct or incorrect hypothesis.

DAYS TWO AND THREE
15. Allow students a few minutes to make observations. They need time to move the water into the graduated cylinder to measure the non-evaporated water volume. They need to subtract the water volume from the initial 100mL to derive the evaporated amount of water. After day three, the students should complete the investigation, draw a conclusion, and complete the critical thinking questions at the end of the Evaporation Marathon Lab Investigation. (See Associated File) Collect questions and formatively assess, providing corrective feedback as necessary.

16. Return the data chart and critical thinking questions. Bring closure to the lab by allowing students to identify the variables in the lab. The independent variable (container size) and the dependent variable (time for evaporation to occur). Ask them to share why the constant (the amount of water) was important to the success of this experiment. (It is important to test one variable at a time. It was important to use the same amount of water in each container, so that the data would represent container size not water amount.)

17. Help students to see that the surface area of the container was a factor in the evaporation of the water. The larger the surface area, the faster the water evaporates.

#### Assessments

1. The Evaporation Marathon Investigation Lab sheets (See Associated File) contain critical thinking questions and are used as a formative assessment for students to identify the dependent and independent variables in an experiment. They are also used to assess students’ ability to use appropriate experimental design, with consideration for rules, time, and materials required to solve a problem.
2. Use the Teacher Assessment Guide and the Goal 3 Standards Checklist to assess students' abilities to work cooperatively with others in an effective and productive manner, and to assess if they demonstrate creative and critical thinking skills to solve a problem.

#### Extensions

1. This is a great lab to integrate the mathematical standards for finding the area of a circle. This lab could be extended to include four or five containers with circular surfaces so that the students could derive the surface area (top only) of the containers by using the formula for the area of a circle: The area of a circle is equal to 3.14 (pi) multiplied by the radius squared.
2. It is also a good lesson to introduce graphing independent and dependent variables. The independent variable is plotted on the horizontal axis also known as the abscissa or x-axis, and the dependent variable is plotted on the vertical axis also known as the ordinate or y-axis.