Surface Tension - Floating Pepper Scatter (Mark Rothenay/Ryan Hendrickson)
Author
Mark Rothenay / Ryan Hendrickson
Principle(s) Illustrated
Surface Tension
Hydrogen Bonding
Density
Standards
SEPs
1. Asking questions (for science) and defining problems (for engineering)
3. Planning and carrying out investigations
6. Constructing explanations (for science) and designing solutions (for engineering)
7. Engaging in argument from evidence
8. Obtaining, evaluating, and communicating information
CCCs
2. Cause and effect: Mechanism and explanation. Events have causes, sometimes simple, sometimes multifaceted. A major activity of science is investigating and explaining causal relationships and the mechanisms by which they are mediated. Such mechanisms can then be tested across given contexts and used to predict and explain events in new contexts.
5. Energy and matter: Flows, cycles, and conservation. Tracking fluxes of energy and matter into, out of, and within systems helps one understand the systems’ possibilities and limitations
Chemistry 9-12: Chemical bonding
2h. * Students know how to identify solids and liquids held together by van der Waals forces or hydrogen bonding and relate these forces to volatility and boiling/ melting point temperatures.
Questioning Script
Prior knowledge & experience:
Basic understanding of the properties of water, density and surface tension.
Root question:
1. What will happen when a pepper is placed into a cup of water?
2. What do you believe will happen when you place soap inside the water with the pepper?
Target response:
The pepper will initially float on the surface of the water due to the surface tension of the water. This is due to the cohesive forces water molecules have for one another. The molecules at the surface of the water do not have other water molecules on all sides of them and consequently they cohere more strongly to those directly associated with them (in this case, next to and below them, but not above). Once the liquid soap is introduced, the surface tension between the water molecules breaks and the up-most water molecules will now be pulled to the sides of the container. This will also cause the pepper that was on top of these water molecules to also move away from where the soap was applied.
Common Misconceptions:
The pepper will always sink.
The liquid soap will cause bubbles to form.