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The module is focused on the essential ability of water to dissolve and transport some substances and not others, and on the molecular properties underlying these phenomena. Students are asked to reason using the kinetic molecular theory. The power of the kinetic molecular theory in understanding matter in solutions lies in helping students understand that matter does not simply disappear when it is dissolved, but rather remains in the form of hydrated ions and hydrated larger molecules.
Students will be able to understand that:
1a. Suppose you have three cups of water. In the first cup you add a teaspoon of vegetable oil, in the second cup you add a teaspoon of sugar, and in the third cup you add a teaspoon of very fine sand. You then shake each cup vigorously and let them stand for two hours.
Describe what is happening to the ingredients in each cup immediately after shaking. Then describe what is happening to each ingredient -- including water -- in each cup two hours after shaking the material.
1b. Did the oil, sugar, and/or the sand dissolve? Explain your answer. Be specific as to the forces and interactions that are responsible for dissolving.
2a. Why do vegetables wilt when you put them in salt water?
3a. What happens to salt on an atomic level (include molecules and ions in your description) when it dissolves in water? Describe the way in which the salt and the water interact.
3b. Alcohol is slightly polar. What happens to salt on an atomic level when it is placed in alcohol?
3c. Draw a picture that shows a salt solution in water. Be sure to label your picture or provide a key for any symbol you use.
3d. Draw a picture that shows a salt solution in alcohol. Be sure to label your picture or provide a key for any symbol you use.
4a. Suppose you have a container in which you place 1000 water molecules on the left side of a wall and on the right side 900 water molecules and 100 NaCl molecules (200 ions). Then you remove the wall. How many molecules of water would end up on each side of the container? How many ions would end up on each side of the container?
4b. Now start over again with a water-permeable wall (it lets water flow through it, but not salt) in the container. You place 1000 water molecules on the left side of the wall and on the right side 900 water molecules and 100 NaCl molecules (200 ions). How many molecules of water would end up on each side of the container? How many ions would end up on each side of the container?
4c. If you could take a movie of the molecules and ions in the container with the water-permeable wall, what would you see if you watched the movie? Be specific as to the forces driving any changes that occur.
includes extensions, etc.
Other concept maps include:
There are special forces that contribute to the particular ways materials act in solutions. Molecules in liquids no longer act freely, as they do in a gas, but are constrained by strong and weak forces.
Additional Related Concepts