Author

Wendy Banner 1.

Principle(s) Illustrated

1. Macro scale properties related to micro scale structure.

2. Polar and non-polar liquids / Cohesion vs. adhesion

3. Particle theory of matter

4. Colligative properties of water (in living systems…)

Standards

8: 3.e. States of Matter.

8: 6.c. Molecules of living systems.

8:7.c. Classification of matter by properties

CHEM: 2.f. Bonds & shape of simple molecules and their polarity.

Questioning Script

Part A.

1. Describe and draw the appearance of the red liquid.

2. Describe the behavior of the red liquid. How foes it relate to itself?

To the wood pick? To the plastic baggy?

3. What do you think the atoms or molecules are doing based on your observations?

Part B.

1. Describe and draw the appearance of the blue liquid.

2. Describe the behavior of the bllue liquid.

3. Based on your observation, what do you think the atoms/molecules are doing?

Part C.

1. Predict what will happen if the two are mixed. Can they mix?

2. Will the result act more like the red or the blue liquid?

3. Describe what happened when you slowly dragged the red to meet the blue.

4. Make an inference about it and draw what you think the particles are doing.

Part D.

EXTENSION: Capillary action and chromatography.

Prior knowledge & experience:

• Matter in liquid form is made up of particles.

• Structure of atoms (?)

• Students have observed that water beads up on some surfaces.

• Some students compare the attraction to magnets

Root question:

• Why do the liquids differ?

• Can they mix?

• What property will win if mix?

• Extension: Why do the colors separate in the paper towel?

Target response:

Part A.

• Itself - polar water molecules display strong cohesion.

• The wood pick – water shows adhesion with hydrophilic wood fibers.

• The plastic surface –water resists plating out on hydrophobic plastic.

Part B.

• The non-polar alcohol will splay out in all directions when prodded by the pick. No cohesion.

• The molecules are not attracted to the wood fiber. No adhesion.

• The liquid does not resist, (glide over) the plastic surface, it sticks.

Part C.

• Attractive forces of water molecules try to maintain hydrogen bond patterns while the random motion of the alcohol molecules “infiltrate the matrix”.

Common Misconceptions:

• Students tend to think the molecules of a liquid are themselves suspended in a liquid.

• Students think the water/alcohol molecules become red/blue. (vs solutes dyes)

• They think the stickiness is a result of more chemical bonds .

• They interpret the effect as viscosity and draw huge tangled molecules of polymers.

• Extension: Chromatography; Students think the 2 liquids are trying to separate.

Photographs and Movies