Enrichment Lesson: Sticky Water

ACTIVITY 1 - ACTIVITY 2

ACTIVITY 1: Overview
Although a water molecule has an overall neutral charge, the actual structure of a water molecule makes it a polar molecule. The polarity of the water molecule causes it to be attracted to other water molecules as well as molecules of other substances. The attraction between water molecules is called cohesion. The attraction of water molecules to other substances, like soil or glass, is called adhesion. The cohesive force that occurs between water molecules is so strong that when comes in contact with another medium, such as air, the water creates a "sticky skin", which is known as surface tension. These bonds are so strong that they can support insects, you may have seen this before demonstrated by a water strider.

Objectives
Students will:

experiment with the adhesive and cohesive properties of water

Time
One or two 45 minute class periods.

Materials

plastic cups or beakers to hold water coins (pennies, nickels, dimes) eyedroppers paper towels "Sticky Water" worksheet Downloadable version: stickywaterworksheet.doc - stickywaterworksheet.pdf

Procedure

Divide students into teams of two. Give each pair a coin, an eyedropper, a cup or beaker of water, and paper towels.   Have the teams predict how many drops of water they will be able to put on the coin.   Allow the students to slowly begin to place drops of water on the coin. Tell the students to add the drops one drop at a time for better results. Students will count the drops, and continue to add drops until the surface tension breaks, the water drop collapses, and spills over the side on the coin.   Have the students record the number of drops they were able to successfully place on the penny before the water drop collapsed.   Allow the other student on the team to repeat the activity.   Students report their team's data to the class.

Assessment Suggestions
Analyze the data. The following questions may help prompt the students' analysis:

• Did the number of drops change with the size of the coin?
• Did the number of drops change by using the "heads" side versus the "tails" side of the coin?
• Did using a new coin differ from using an older (more used and worn down) coin? Why?
• What does this property of water have to do with water quality? What else do you think could "stick" to water molecules?

Extension:
Complete the same activity with salt water, sugar water, or other liquids. Compare those results with those collected from using plain water. Are there any differences? Why?

ACTIVITY 2: Overview
Although a water molecule has an overall neutral charge, the actual structure of a water molecule makes it a polar molecule. The polarity of the water molecule causes it to be attracted to other water molecules as well as molecules of other substances. The attraction between water molecules is called cohesion. The attraction of water molecules to other substances, like soil or glass, is called adhesion. The cohesive force that occurs between water molecules is so strong that when comes in contact with another medium, such as air, the water creates a "sticky skin", which is known as surface tension. These bonds are so strong that they can support insects, you may have seen this before demonstrated by a water strider.

Objectives
Students will:

experiment with the adhesive and cohesive properties of water

Time
One or two 45 minute class periods.

Materials

plastic cups or beakers to hold water paperclips forks paper towels "Sticky Water" worksheet Downloadable version: stickywaterworksheet.doc - stickywaterworksheet.pdf

Procedure

Divide students into teams of two. Give each pair paperclips, a fork, a cup or beaker of water, and paper towels.   Have the teams predict how many paperclips they will be able to float on top of the water.   Have the students attempt to place a paperclip on the surface of the water in the cup. (Hint: Have the students place the paperclip on the prongs of the fork, and gently lower onto the water).   Have the students place as many paperclips as possible onto the surface of the water. Record the number of paperclips.   Allow the other student in the team to repeat the activity.   Students report their team's data to the class.

Assessment Suggestions
Analyze the data. The following questions may help prompt the students' analysis:

• Why do you think the paperclips "float"?
• Could the method used to place the paper clips in the water change the results? Why?
• What insects/invertebrates use this property of water to their advantage? How?

Extension:
Complete the same activity with salt water, sugar water, or other liquids. Compare those results with those collected from using plain water. Are there any differences? Why? Do you think this has an effect on the organisms living in the water?

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