Evaporation: Investigating factors that affect it
In this inquiry or guided inquiry (depending on grade level) investigation, students will examine conditions to see what affect these conditions have on evaporation rates. Students will keep a science journal of their investigation. Students will then create a chart showing the various influences on evaporation.
Cause and effect
Context for Use
This "hands-on" part of the investigation will be completed in 2-3 days of 20-30 minute class times. This investigation can be teacher demonstrated entirely, OR all student-performed, OR a combination of both depending on supplies available, time allotted, and grade level. Some time is needed to comprise testable questions regarding evaporation, and then additional time to perform each aspect of the investigations. A final day is needed to "wind up" the discussion and to come up with a hypothesis regarding each factor that affects evaporation.
Resource Type: Activities:Classroom Activity
Grade Level: Intermediate (3-5)
Description and Teaching Materials
A meter stick to make a balance (or a wood slat will work fine also.)
A balance support
A heat source (hot plate)
Hair dryer or fan
Beakers or glass jars
Rubbing alcohol (enough to soak one sponge)
Sponges (5cm x 10cm each) 2
Watch or clock
Ice cubes or COLD water
Watch glass (best)or glass plate large enough to cover a beaker or jar
**(Additional materials for investigations thought up by the students)
Begin investigation with a discussion on what evaporation is and what factors affect the rate of evaporation. What are the "things" that could affect evaporation? How could we test these "things". (Students, hopefully, will come up with wind, heat, humidity, and the nature of the liquid that is being evaporated.) This can be teacher guided or not.
Set up experiments (teacher guided) for the following using a balance beam made up of a meter stick or wood slat balanced on a support of some kind (guided instruction?). This can be a "knife-edge" balance that is made for this purpose, or it can be created with a stack books and then a triangular ruler on top (or something similar) for the fulcrum of the balance.
Take 2 paperclips (made into a hook) one for each end of the balance and hang a piece of sponge (that has been soaking in water for at least 1 minute) on each end of the balance, and using the paperclip hooks, slide them together or apart until the balance "balances".
Test for the effect of various factors on the rate of evaporation as follows:
A. Wind: Set up the fan or hair dryer on low speed so that it blows on one of the
sponges for 2 minutes. Observe. (If no visible effect is noticed in the balanced
apparatus, allow the fan to continue to blow until the effect is seen.)
B. Heat: Re-soak the sponges and re-balance them. This time, place the heat source
under one of the sponges. (Keep it far enough away to avoid overheating the
sponge. Observe after 2 minutes. (Use more time of necessary)
C. Humidity: Re-soak the sponges and re-balance them. Suspend one sponge in a
beaker (jar) that has about an inch of water in the bottom of it. Do not allow
the sponge to touch the water or the sides of the container. (Ask students why
you should be careful of this.) Allow time for evaporation and observe.
D. Nature of the evaporating liquid: Wring out both sponges (or use dry ones). If
you use wet ones, blot with paper towels to remove as much moisture as
possible. Soak one sponge in water and the other in rubbing alcohol. Allow 2
minutes for evaporation to occur and observe. (More time if necessary)
Demonstrate the evaporation and condensation process:
A. Add about 250 ml of water to the beaker and place it on a hot plate over medium heat.
B. Place the watch glass (glass plate) on top of the beaker.
C. Place an ice cube (or very COLD water) in the watch glass. (If you use cold
water instead of ice, allow the water in the beaker to heat for awhile before
putting the cold water on the watch glass for better results.)
Prior to each of these activities solicit questions and or answers for what is about
After each activity solicit reasons for the behavior of the materials and encourage
additional questions regarding what has happened.
Discuss the results of the investigation and students can write their own conclusions to the investigation in their science journals.
Teaching Notes and Tips
If you want to speed up the investigation, groups can be assigned different aspects of the investigation and then share their results and conclusions. These conclusions then can then be evaluated by the other groups and discussed.
A safety issue to note is the use of hotplates and heated (possibly boiling) water.
Some prior discussion and/or experience with balances and what they do should take place for students to understand why the balance is used in this investigation.
In the past, I have lectured about the aspects of evaporation. Most of the questions I have received regarding the process of evaporation are investigated in this activity. In this exercise, students will receive first-hand experience with the factors involved in evaporation.
* Students ability to write inquiring questions in their journal and then plan how they will answer their questions.
* Students will hand in a statement (hypothesis) regarding evaporation and the factors affecting it.
* Informally assessing how student work in groups and interact with each other.