Overview
This document outlines experiments demonstrating intermolecular forces, specifically focusing on the interaction of oil and water, surface tension, and additional demonstrations involving various liquids.
Experiment 1: Oil and Water Miscibility
Materials
- Bottle of hexanes (half full)
- Mineral oil
- Bottle of water (half full, dyed lightly with methylene blue)
- Palmolive dish detergent
- Clear drinking glass (preferably glass)
- Cheesecloth
- Cardboard square with waxed surface
Procedure
- Miscibility Experiment:
- Mix hexanes and dyed water in a clear drinking glass.
- Observe that the two liquids do not mix (immiscible). They separate quickly after shaking.
- Discuss why this occurs: water molecules are more strongly attracted to each other than to hexane molecules.
- Soap Addition:
- Add Palmolive dish detergent to the mixture.
- Mix again and observe that the layers combine temporarily.
- Discuss the role of soap: it has a long oily end that resembles hexanes and a polar end that dissolves in water. This helps emulsify the two liquids temporarily.
Reference
- Include pages from the textbook showing soap structure and micelle formation.
Experiment 2: Surface Tension
Materials
- Clear drinking glass
- Cheesecloth
- Cardboard square
Procedure
- Cardboard and Water Demo:
- Demonstrate the physics trick of placing cardboard over a full glass of water and flipping it.
- Discuss air pressure and vacuum creation as an explanation.
- Cheesecloth Experiment:
- Drape cheesecloth over the glass.
- Flip the glass with the cheesecloth and remove the cardboard.
- Observe how water remains in the glass despite the holes in the cheesecloth.
Explanation
- Explain that water molecules adhere to the threads of cheesecloth, supported by strong hydrogen bonds among the water molecules, which, along with air pressure, allows them to stay in place over the gaps.
Additional Demonstrations
1. Magic Sand
- Demonstrate the properties of magic sand and its unique behavior with water.
2. Float Pin
- Use a float pin to illustrate principles of buoyancy and surface tension.
3. Rates of Evaporation
- Compare the evaporation rates of pentane, 3-pentanone, and 1-pentanol using a temperature probe.
4. Bending Solutions
- Charge a glass rod with wool and place it alongside streams of pentane, 3-pentanone, and 1-pentanol in separate burettes (10 mL each).
- Observe the bending behavior of each solution:
- Pentanol bends significantly.
- Pentanone bends weakly.
- Pentane does not bend.
5. Viscosity
- Use a large piece of acrylic backed with white paper to place various liquids (motor oil, molasses, honey, corn syrup, colored water).
- Raise the acrylic and have students predict which liquids will flow fastest/slowest.
Addendum: Properties and Comparisons of Various Substances
Honey
- Contains maltose and glucose.
Syrups
- Molasses
- Corn Syrup
Oils
- Motor Oil
Spreads
- Marmite
Sand
Types
- Ordinary Sand
- Magic Sand
- Achieved by covering ordinary beach sand with tiny particles of pure silica and exposing them to vapors of trimethylsilanol ((CH_3)_3SiOH), an organosilicon compound.
- The trimethylsilane bonds to the silica particles while forming water, resulting in sand grains coated with hydrophobic groups.
Chemical Interactions
- Hydrogen Bonding: Occurs between protein strands.
Soap Micelle
A structure formed by soap molecules that can trap and emulsify fats and oils, illustrating the interaction of hydrophilic and hydrophobic properties.