Water: a Lesson in Polarity and Solubility

a guided inquiry lesson modeled after the POGIL style

Pascack Hills High School, New Jersey

Summer Research Program for Science Teachers

August 2007

Objective:

Students will be able to describe what happens on the atomic/molecular level when water molecules interact with each other, with soluble salts, and insoluble materials.

Materials:

Procedure:

Divide students into groups of 2-4 students each. Each student should receive his/her own copy of the questions and information. The instructor should truly be the facilitator, allowing students within and between groups to answer questions and address tangents and misconceptions whenever possible.

Information students might find useful:

Definitions (from http://dictionary.reference.com)

• dissolve:  to disintegrate, break up, or disperse

• soluble: capable of being dissolved

Carefully observe the models with everything you do!!!

A1. Water

Before you is a beaker of water. Observe the water inside the beaker. Stir the water. Then scoop the water out. Scoop the water back into the beaker. This time pour the water onto the desk.

Q1: How do you know that these models represent water molecules?

Q2: How do the water molecules interact with each other? What about the models is making them do this?

Q3: Draw the Lewis dot structure of water. What about water would make it behave the way the models do?

A2. Table Salt and Water

Return the water to the beaker. Take your crystal of table salt and drop it in the water. Mix it around a bit, then remove the NaCl from the water and place it on the desk. Take some of the water out of the beaker and investigate the way the salt and water interact.

Q4: Which particle represents the sodium ion? How do you know?

Q5: Which particle represents the chloride ion? How do you know?

Use the models to show how table salt dissolves in water. Check with the teacher to see if you are on the right track.

Q6: Sketch, using Lewis dot structures, the process by which salt dissolves. Use the cartoon boxes (create more if necessary) to show the passage of time. Label the components of your sketch!

Q7: Describe how a real beaker of water would look if table salt were dissolved in it. How does this compare with your model/drawing? Explain.

A3. Ethane and Water

Replace the water in the beaker. (You will not need your salt any longer.) Add the molecule of ethane to the water.

Q8: Describe the interaction of the ethane model with the water models.

Q9: Will ethane dissolve in water? Explain. (You may use a comparison with your observations of salt in water to answer this question.)

Q10: Describe how a real beaker of water would look if ethane were mixed with it. Explain.

A4. States of Matter

Separate one water molecule from the other water molecules. Then remove an ion from your crystal of table salt. Get together with another group, place your ethane molecules together, and then separate them.

Q11: Which particles are hardest to separate? Which are easiest to separate?

Q12: What is the state of matter of each of these three substances at room temperature? Explain your answer based on common knowledge and what you observed with these models.

Exercises:

E1: Was the surface of the water models smooth? Did the water models coat the entire inside of the beaker? Explain why this is different from what you observe with “real” water.

Consider the process by which water freezes. Use the water models on your desk to help you.

E2: What happens to the velocity of the water molecules?

E3: How would the water particles arrange themselves as they form ice that would be different from the way they were arranged as a liquid in the beaker? Why would this difference occur?

E4: Based on your experience in this activity, how were these models good for understanding the behavior of water and its interaction with salt and ethane? In what way were the models insufficient for demonstrating water’s behavior?

National Science Standards:

Content Standards A (Science as Inquiry)

Content Standards B (Physical Science)

Content Standards G (History and Nature of Science)