Comprehensive Notes on Water Properties and Macromolecules

Activity: Rubbing a balloon and bringing it near a stream of water.
Observation: The water stream bends towards the balloon.
Explanation:
- Rubbing the balloon gives it an electrical charge (e.g., positive).
- Water is a polar molecule, meaning it has slightly positive (hydrogen atoms) and slightly negative (oxygen atom) ends due to uneven electron sharing.
- The charged balloon attracts the oppositely charged parts of the water molecules.
- This attraction pulls the water stream towards the balloon.
Properties Demonstrated: Water's polarity and a form of adhesion (attraction between water molecules and other substances, even without direct contact).

Activity: Observing water rise in a narrow tube.
Phenomenon: The water going up the tube is called capillary action.
Explanation:
- Adhesion: Water molecules stick to the inside surface of the tube (the attraction between water and the tube's material).
- Cohesion: As water molecules adhere to the sides, they pull other adjacent water molecules (not directly touching the tube) upwards with them due to the strong attraction between water molecules.
Biology Connection: This is how plants get their water.
- Plants do not actively pump water; water moves passively from the roots (in the ground) up the plant's vascular tissue through capillary action.

Activity: Attempting to dissolve salt in water versus oil.
Observation: Salt dissolves in water but remains separate from oil, and even after significant time, oil does not dissolve salt.
Properties Demonstrated: Water as a universal solvent.
Explanation:
- Water is an excellent solvent due to its polar properties (positive and negative charges).
- Water molecules use their opposite charges to attract and pull apart the ions of ionic compounds (e.g., table salt, which is Na^+ and Cl^-, connected as a crystal).
- The negative end of water attaches to the positive ion (Na^+), and the positive end attaches to the negative ion (Cl^-), effectively dissolving the salt.
- Oil is nonpolar (specifically, it is a lipid macromolecule).
- Nonpolar substances lack the necessary charges to attract and separate the ions in salt, hence oil cannot dissolve salt.
Biological Importance: Water's solvent properties are crucial for life.
- All living things contain water.
- Water helps transport essential ionic nutrients throughout an organism's body (e.g., blood transports nutrients and ions).

Activity: Dipping a Q-tip in alcohol and water, then observing which dries faster.
Observation: Water takes significantly longer to evaporate than alcohol.
Explanation:
- When substances transition from liquid to gas, their molecules must overcome the attractive forces holding them together.
- Water molecules have stronger attractive forces (hydrogen bonds) between them compared to alcohol molecules.
- Therefore, water requires more energy (heat) to overcome these attractions and evaporate.
- Alcohol has weaker attractions, making it more volatile (evaporates easily, e.g., acetone in nail polish remover).
Biology Connections:
- Water Cycle: Water's resistance to evaporation ensures it remains in liquid form longer, crucial for ecological processes.
- Temperature Regulation (Evaporative Cooling): This property is vital for living systems, particularly in functions like sweating.
  - Sweat (water) on the skin absorbs a large amount of heat energy from the body to cause it to evaporate.
  - This absorption of body heat during evaporation leads to a cooling effect.
  - In humid environments, evaporation is hindered, making sweating less effective at cooling the body.

Activity: Gently floating a pipette on water, then adding soap.
Observation: A carefully placed pipette can float on water due to surface tension. Adding soap causes it to sink.
Property Demonstrated: Surface tension (caused by cohesion).
Explanation:
- The pipette floats not because it's less dense than water (it can sink), but because it gently rests on the undisturbed, tightly cohesive layer of water molecules at the surface.
- Cohesion: The strong attractive forces between water molecules pull them tightly together, forming a