BIO 120 u1 p1.5

Properties of Water and Their Implications

1. Overview of Water's Role in the Midwest Climate

  • Humidity Contribution:

    • In the Midwest, corn plays a significant role in contributing to local humidity levels during summer months (July and August).

    • Mechanism:

      • Corn evaporates water to cool itself, releasing significant amounts of water vapor into the atmosphere.

      • This process leads to an increase in humidity, making summer conditions feel uncomfortable.

2. Physical Properties of Water

  • Resistance to Temperature Change:

    • Water exhibits resistance to temperature changes due to its high specific heat capacity and heat of vaporization.

    • Specific Heat Capacity:

      • The amount of heat required to raise the temperature of a substance. Water has a high specific heat capacity, allowing it to stabilize temperatures in various environments.

    • Heat of Vaporization:

      • The energy required for water to transition from a liquid to a gas, crucial for organisms in hot climates.

3. Water as the Solvent of Life

  • Versatile Solvent:

    • Water is often referred to as the solvent of life due to its ability to dissolve numerous substances, facilitating biochemical processes.

    • Definition of a Solvent:

      • A solvent is a substance in which other substances (solutes) dissolve.

  • Composition of Blood as an Example of Solvent Properties:

    • Human blood is primarily made up of water and contains various components:

    • Components of Blood:

      • Red blood cells: Carry oxygen.

      • White blood cells: Play a role in the immune response and healing.

      • Plasma: A fluid component that dissolves gases, waste products, nutrients, proteins, ions, etc.

    • Water's Role:

    • Approximately 60% of the human body is composed of water, aiding in transporting nutrients and gases essential for survival.

4. Definitions of Solvents and Solutes

  • Solvent:

    • The substance that dissolves solutes.

  • Solute:

    • Substances that are dissolved in a solvent (e.g., salts like table salt and sugars).

    • Examples:

    • Sugar dissolving in coffee demonstrates water's capability as a solvent.

  • Solution:

    • A homogeneous mixture of solute and solvent, resulting in an even distribution of solute.

    • Homogeneous:

      • Means uniform in composition; every sip tastes the same.

  • Aqueous Solution:

    • Solutions where water is the solvent (e.g., saltwater, where NaCl dissolves in water).

5. Ionic Dissolution in Water

  • Hydration Shell Formation:

    • When ions like sodium ( ext{Na}^+) and chloride ( ext{Cl}^-) dissolve in water:

    • Water molecules surround the ions, forming hydration shells which allow them to remain in solution.

  • Ionic Structure of Table Salt (NaCl):

    • Sodium ion: ext{Na}^+

    • Chloride ion: ext{Cl}^-

    • Interaction with water molecules leads to dissolution through attraction of partial charges:

    • Partial negative of oxygen attracted to ext{Na}^+

    • Partial positive of hydrogen attracted to ext{Cl}^-

6. Relationship Between Polarity and Solubility

  • Polarity of Water (H₂O):

    • Defined by unequal sharing of electrons, leading to partial charges:

    • Oxygen (more electronegative) attracts electrons, giving it a partial negative charge.

    • Hydrogens receive partial positive charges.

  • Hydrophobic vs. Hydrophilic Molecules:

    • Hydrophobic Molecules:

    • Water-fearing, typically nonpolar substances that do not dissolve in water (e.g., fats and oils).

    • Example: Oil and water do not mix, forming separate layers.

    • Hydrophilic Molecules:

    • Water-loving, usually polar substances that dissolve well in water (e.g., salts and sugars).

    • Example: Sugar readily dissolves in water.

7. pH and Water Chemistry

  • Dissociation of Water:

    • Water can dissociate into hydroxide ions (OH⁻) and hydrogen ions (H⁺), a reversible reaction that contributes to pH levels in solutions.

  • Definition of pH:

    • A scale measuring acidity or alkalinity, ranging from 0 to 14. A neutral pH is 7.

    • Acids:

      • High concentration of hydrogen ions (H⁺); examples include citric acid in orange juice and battery acid.

    • Bases:

      • High concentration of hydroxide ions (OH⁻); examples include bleach and baking soda.

    • Neutral Solutions:

      • Solutions with equal concentrations of H⁺ and OH⁻, such as pure water and human blood.

8. Buffer Systems in the Human Body

  • Buffers:

    • Substances that help maintain pH balance in biological systems by neutralizing acids or bases.

    • Carbonic Acid (H₂CO₃):

      • Released when blood is too alkaline, contributing H⁺ ions to increase acidity.

    • Bicarbonate Ion (HCO₃⁻):

      • Acts when blood is too acidic, accepting excess H⁺ ions.

  • Importance of pH Homeostasis:

    • Maintaining a constant pH is vital for cellular activities and overall health.

9. Ocean Acidification

  • Impact of Carbon Emissions:

    • Increased atmospheric CO₂ from fossil fuel use dissolves in oceans, forming carbonic acid (H₂CO₃).

    • This results in decreased pH of ocean waters, adversely affecting marine life, particularly coral reefs.

  • Coral Bleaching:

    • Carbonic acid leads to the depletion of carbonate ions, crucial for coral survival, resulting in bleaching and mortality of coral.

  • Mitigation Efforts:

    • Success in growing coral in nurseries for transplanting to damaged areas.

    • Emphasis on the need for lifestyle changes to reduce carbon footprints and protect natural resources.

10. Summary of Essential Properties of Water

  • Key Properties:

    • Hydrogen bonds lead to water's unique properties:

    • Cohesion and adhesion

    • High heat capacity

    • Lower density as a solid than a liquid

    • Versatile solvent capabilities

  • Understanding water’s structure and polarity is fundamental to grasping its chemical behavior and ecological importance.