Lesson 2: Water and Its Characteristics

Activities

Activity 1: The Water Molecule

In today's reading you learned about cohesion, polarity, and surface tension. Understanding these concepts is important to understanding the relationships of non-living components of the hydrosphere with living components of the water planet. For this activity, you will develop a diagram of a water molecule and label some of its parts. Creating a diagram of the water molecule is important for a couple of reasons. First, the actual size of molecules makes it impossible to see them without the presence of very specialized and expensive equipment. Second, understanding concepts such as polarity and cohesion is made easier by being able to look at and think in terms of a visual representation, specifically a two-dimensional model. Ask your parent which option of this activity to complete.

The water molecule diagram that your child will create is a very basic introduction to molecular diagrams and some concepts associated with them. The model activity has three different options. Option 1 is adequate for the understanding of polarity and cohesion, giving your child a visual image of what a water molecule looks like and the location of the poles and different components of the water molecule. Option 2 requires your child to think a little more abstractly by making her own drawing before labeling it. Option 3 is the most advanced option — it is challenging because of the addition of the outer shell electrons to the diagram. This option will also require your child to use her understanding of chemical bonds (ionic, covalent) to complete it.

Option 1: The Water Molecule and Its Components

While it is likely that you will not see an actual water molecule, having a visual representation of the molecule will be useful as you think about polarity, cohesion, and surface tension. An easy way to remember the shape of a water molecule is to think of Mickey Mouse© ears. The oxygen atom is like the head of the mouse, and the hydrogen atoms are much like the ears. As you label your diagram, keep this image in mind.

Using the "Water Molecule" (Option 1) activity sheet, you will label the following parts of the water molecule:

Hydrogen atom (H)
Oxygen atom (O)
Negative pole (-)
Positive pole (+)

As you are labeling the diagram, keep in mind what you have read about polarity. Take a moment to consider the following idea.

Assume that you have two water molecules. At the bottom of the activity page, draw an illustration that shows how the water molecules would line up if they were close to each other. Keep in mind that the polarity of the molecules means they have both positive and negative poles.

NOTE: If it will help, think about two magnets, with the north pole being positive and the south pole being negative.

Student Activity Page

Water Molecule (Option 1)

Your child labeled a water molecule diagram and then drew an illustration of how water molecules line up when close together. Her illustration should show that she understands that the water molecule has a positive pole and a negative pole and that the positive pole will weakly bond with the negative pole of another water molecule.

Answer Key - Water Polarity

Your child's drawing may look different than this one. Look for the negatively charged oxygen molecules to be lined up with the positively charged hydrogen molecules.

Optionally, you can ask your child to think about whether her illustration shows the water to be in a solid or liquid state.

The illustration for Option 3 may also be useful in checking your child's work.

Option 2: Drawing a Water Molecule from Scratch

Using a blank sheet of paper, draw a diagram of a water molecule and label the following:

Hydrogen atom (H)
Oxygen atom (O)
Negative pole (-)
Positive pole (+)

As you are labeling your diagram, keep in mind what you have read about polarity. Take a moment to consider the following idea.

Assume that you have two water molecules. Draw an illustration that shows how the water molecules would line up if they were close to each other. Keep in mind that the polarity of the molecules means they have both positive and negative poles.

NOTE: If it will help, think about two magnets, with the north pole being positive and the south pole being negative.

For this activity, your child will be thinking a little more abstractly than in Option 1 as she will have to recall and produce an image that is an adequate representation of a water molecule as well as label it. Refer to the answer key for Option 3 to get an idea of what the diagram should look like.

Your child also drew an illustration of how water molecules line up when close together. Her illustration should show that she understands that the water molecule has a positive pole and a negative pole and that the positive pole will weakly bond with the negative pole of another water molecule. Refer to the web link in Option 1 for an idea of what this should look like. Optionally, you can ask your child to think about whether her illustration shows the water to be in a solid or liquid state.

Option 3: Advanced Look at a Water Molecule

Using a blank sheet of paper, draw a diagram of a water molecule and label the following:

Hydrogen atom (H)
Oxygen atom (O)
Negative pole (-)
Positive pole (+)

In the diagram, you will also determine and label what kind of bond occurs between the hydrogen and oxygen molecules. The final component you will add to the diagram is the outer shell electrons of the atoms in the water molecule. Based on the type of bond that is occurring, are the outer shell electrons being shared by the hydrogen and oxygen atoms, or have they moved from one atom (hydrogen) to the other (oxygen)?

As you are labeling the diagram you drew, keep in mind what you have read about polarity. Take a moment to consider the following idea. Assume that you have two water molecules. Draw an illustration that shows how the water molecules would line up if they were close to each other. Keep in mind that the polarity of the molecules means they have both positive and negative poles.

NOTE: If it will help, think about two magnets, with the north pole being positive and the south pole being negative.

Option 3 is focused on further developing your child's understanding of some basic principles associated with chemistry. The earlier concepts like these are introduced, the greater the likelihood that your child will be able to deal with the complexities associated with chemistry — a discipline that requires a lot of abstract visualizations. By developing your child's selective coding ability with new information, the likelihood of understanding chemistry increases.

The bond in water molecules is covalent. Refer to the following answer key to check your child's diagram and labels.

Your child also drew an illustration of how water molecules line up when close together. Her illustration should show that she understands that the water molecule has a positive pole and a negative pole and that the positive pole will weakly bond with the negative pole of another water molecule. Refer to the web link in Option 1 for an idea of what this should look like. Optionally, you can ask your child to think about whether her illustration shows the water to be in a solid or liquid state.

Answer Key

Activity 2: Full or Empty?

Materials: 10-12 quarters, nickels, and pennies, saline solution, rubbing alcohol, clear diet soda, or other solution*, tall drinking glass

In this activity, you will work with surface tension. Ask your parent which option to complete.

This activity explores the properties of surface tension and cohesion found in water. Option 1 will take less time and explores these properties in water only. Option 2 is more comprehensive and allows your child to explore these properties in other solutions. Choose the option that best fits your child.

Option 1

For this activity, you will need 10-12 pennies, 10-12 nickels, and 10-12 quarters as well as a glass full of water. The glass should be filled to the very rim, with a slightly convex (curved outward or bulging) shape to the surface of the liquid. Follow these steps:

Predict how many quarters you can add to the glass of water before the water overflows. Record your prediction on the table found on the "Full or Empty?" (Option 1) activity page.
Bring one quarter to the center of the glass. Place the narrow edge of the coin in the water and let go. Be very careful in positioning the coin to minimize disruption to the surface of the water.
Repeat Step 2 until the water overflows the glass. Record the number of quarters that you were able to place in the water before it overflowed.
Pour out the water and quarters, refill the glass again, and then repeat Steps 1-3 for nickels and then pennies.

After you have completed the experiment, ponder and answer the following questions:

Even though it seems the water should spill out, briefly explain why it is staying in the cup without spilling.
When predicting the number of coins, how accurate was your guess? Why do you think your guess was off? If it wasn't, briefly explain why your guess was so accurate.
Why did the type of coin influence the results?

Student Activity Page

Full or Empty? (Option 1)

At the end of this activity, your child considered the following questions:

Even though it seems the water should spill out, briefly explain why it is staying in the cup without spilling.
This activity demonstrates two properties of water — cohesion and surface tension — that are a result of a third property, polarity. In this activity your child should make a connection between why the water does not spill and how polarity, cohesion, and surface tension play a role in the water remaining in the glass. Also, if water does spill, ask her to consider what factors may have caused it to spill. NOTE: As a result of cohesion, surface tension exists and overcomes the force of gravity and the force caused by increasing the volume of material in the cup, keeping water in the cup.

When predicting the number of coins, how accurate was your guess? Why do you think your guess was off? If it wasn't, briefly explain why your guess was so accurate.
The guess was off for a few possible reasons. Your child's understanding of surface tension and the bonds shared by water that lead to cohesion was not as clear as it could have been. If the guess was accurate, ask her to explain. If she says it was a guess, push her to explain — use the terms "surface tension" and "cohesion."

Why did the type of coin influence the results?
The number of coins is less important than the fact that the coins take up a certain amount of volume before surface tension changes. Each coin has a different volume. The increase in volume in the cup weakened bonds which also weakened surface tension. As a result, the water spilled out of the cup. The volume has a threshold that weakens the bonds enough to cause the cohesion of the molecules to weaken enough to cause the water to spill. If one were to measure the actual volume of the coins when the water spills, the measurement of volume taken up should be about the same.

Option 2

Before you begin this activity, ponder the following questions:

Does surface tension exist in solutions other than water?
Why does saline solution not have the same cohesion as tap water?

For this investigation, you will need 10-12 pennies, 10-12 nickels, and 10-12 quarters, as well as a glass full of water, and a glass full of an alternative solution. For the alternative solution, you could use saline solution (from Lesson 1), rubbing alcohol, clear diet soda (diet drinks will avoid the stickiness associated with sugar), or another solution. Both the glass of water and the glass of alternative solution should be filled to the very rim, with a slightly convex (curved outward or bulging) shape to the surface of the liquid. Follow these steps:

Predict how many quarters you can add to the glass of water before the water overflows. Record your prediction on the table found on the "Full or Empty?" (Option 2) activity page.
Bring one quarter to the center of the glass. Place the narrow edge of the coin in the water and let go. Be very careful in positioning the coin to minimize disruption to the surface of the water.
Repeat Step 2 until the water overflows the glass. Record the number of quarters that you were able to place in the water before it overflowed.
Pour out the water and quarters, refill the glass again, and then repeat Steps 1-3 for nickels and then pennies.
Repeat Steps 1-4 using the glass of the alternative solution.
Answer the "Questions to Consider" at the bottom of the activity page.

Student Activity Page

Full or Empty? (Option 2)

The activity with the alternate solution will allow students to investigate whether or not a different solution has the same cohesion and surface tension found in water. Students will need to think through the exercise. Review your child's table and discuss the following questions and answers with your child.

Even though it seems the water should spill out, briefly explain why it is staying in the cup without spilling.
This activity demonstrates two properties of water — cohesion and surface tension — that are a result of a third property, polarity. In this activity, your child should make a connection between why the water does not spill and how polarity, cohesion, and surface tension play a role in the water remaining in the glass. Also, if water does spill, ask her to consider what factors may have caused it to spill. NOTE: As a result of cohesion, surface tension exists and overcomes the force of gravity and the force caused by increasing the volume of material in the cup, keeping water in the cup.

Is there a difference in the number of coins based upon the solution used? Why? (Note: In your answer, be sure to use the concepts and/or the terms polarity, cohesion and surface tension.)
Surface tension in the different solutions will either be greater or lesser. In the instance where the surface tension is greater, the expectation should be for the glass to hold more coins. Where the surface tension is less, the expectation should be for the glass to hold fewer coins. When conducting this investigation, your child may or may not see differences in the numbers. If there is no difference, consider the surface tension to basically be the same.

Does surface tension exist in solutions other than water?
It depends. Surface tension is the result of polarity in the molecules that make up a solution. If there is polarity, there is a likelihood of cohesion between the molecules that make up the solution. This cohesion creates surface tension.

Why does saline solution not have the same cohesion as tap water?
In a saline solution, the water has salt crystals that have dissolved. As a result, the parts of the dissolved crystals bond with the water molecules. When the salt bonds with the water, the cohesion of the water is reduced, decreasing or eliminating surface tension.

In instances where the difference is greater than one, ask your child to ponder the role of surface tension as a result of the polarity and cohesion of the molecules in the solution. Ask her to consider if the cohesion is greater or lesser. Greater cohesion means a stronger bond between the molecules in the solution. This increases the surface tension in the solution, allowing the solution in the glass to hold more coins.

Differences may also be the result of the following factors: differing volumes of solution in the glasses or disruption or disturbance of the solutions when adding the coins. The bonds that cause surface tension are very weak, so if the glasses are shaken or the surface of the solution is disturbed enough, the results may change.

Activity 3: Soap Bubbles and Candles (Optional Activity)

Materials: bubbles or detergent solution, candle (kit), funnel (kit)

In this activity, you will put out a candle with a soap bubble.

NOTE: THIS ACTIVITY REQUIRES ADULT SUPERVISION.

This trick demonstrates how much force is caused by the surface tension in a soap bubble. You will need a lit candle, a funnel, and detergent or soap-bubble solution. Follow these steps:

Coat the funnel mouth (the inside part of the large end) with the liquid detergent or bubble solution.
Gently blow a bubble using the small end of the funnel (you should be able to get a nice big bubble, about 12 inches in diameter).
Place your thumb over the small end of the funnel and then remove your thumb. Make sure the bubble remains. Try to do this a couple of times in a row to make sure the bubble does not pop.
With your parent's supervision, bring the small end of the funnel toward the candle. NOTE: If the funnel is small or is slippery from the soap solution, you should ask a parent to perform this step while you observe what happens.

Ponder the following questions:

What characteristic of the molecules in the soap solution allows bubbles to form and remain?
What causes the bubbles to pop?

Soap Bubble Activity

Answers to "Ponder the following questions"

What characteristic of the molecules in the soap solution allow bubbles to form and remain?
The bubble exists because of the presence of cohesion among the molecules that make up the soap. Being a liquid, the soap contains water and other polar components. These polar components result in the forming of the bubble because of surface tension/cohesion. The bubble bursts when the force exerted within or outside the bubble is greater than the cohesion between molecules in the soap solution. At some point in the activity, the students will need to make a connection between polarity/cohesion and understand that this is an illustration of what occurs between water molecules in the liquid state of matter.

What causes the bubbles to pop? When you blow up bubbles, they sometimes pop. The reason is the same as the reason that water spills out of the cups — surface tension and cohesion. The pressure inside the bubble puts a "strain" on the bonds between molecules in the soap bubble. If the pressure is too great, the bubble pops because the surface tension and cohesion between the molecules is not strong enough to hold the molecules together.

NOTE: If the candle causes the bubble to pop, the reason is the same as the second "Question to Ponder." The heat from the candle adds energy to the molecules making up the bubble. When this occurs, the molecules move more. When the energy is great enough, the cohesion between the molecules is not strong enough to keep the molecules in the bubble together. The bonds "break," which can cause the bubble to burst.

Activity 4: Pre-work for Lesson Four

Materials: 2 eggs, small clear cups (kit), vinegar

Now you are going to do some work to get ready for a lesson that you won't complete for two more days. In Lesson 4, you will be doing research into water and estuaries. To prepare for an experiment found in that lesson, follow these directions:

Fill two cups with vinegar.
Place a raw egg (with its shell intact) in each cup of vinegar.
The eggs will need to soak for about 24-48 hours (until the shell dissolves). After 24 hours, check the eggs to make sure they are still intact. Note: Because the eggs can sometimes break, you may want to consider having an extra egg prepared just in case. If for some reason you are unable to prepare an extra egg, choose a portion of the experiment that you would like to conduct and gather as much information as you can.
Do not take the eggs out of the vinegar!

Your child will be preparing for an activity in Lesson 4 by soaking 2 eggs in vinegar for 48 hours. Your child will probably not need help setting up the experiment but may need to be encouraged not to try picking the eggs up for 2 whole days.