Water and Life: Properties, Solutions, and Environmental Impact

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Ch. 3 Water and Life

Properties of Water Molecules

Water is essential for life due to its unique chemical and physical properties, which arise primarily from hydrogen bonding between molecules.

Cohesion: Water molecules stick to each other, resulting in surface tension. This property allows insects to walk on water and supports the movement of water in plants.
Adhesion: Water molecules stick to other substances, facilitating capillary action. This is crucial for transpiration in plants, where water moves upward through vessels.
Transpiration in Plants: The movement of water from roots to leaves, driven by cohesion and adhesion.

Regulation of Temperature

Water helps regulate temperature in organisms and environments due to its high specific heat and heat of vaporization.

High Specific Heat: Water can absorb or release large amounts of heat with minimal temperature change, stabilizing climates and body temperatures.
High Heat of Vaporization: It takes significant energy to convert liquid water to vapor, allowing for cooling mechanisms such as sweating.
Evaporative Cooling: As water evaporates, it removes heat, helping organisms maintain temperature without freezing.

Density and State Changes

Water exhibits unusual behavior when freezing, which is vital for aquatic life.

Lower Density of Ice: Water becomes less dense when frozen due to the arrangement of molecules, causing ice to float and insulate aquatic environments.

Solubility and Solutions

Water is an excellent solvent, especially for polar and ionic substances, due to its polarity.

Hydrophilic Substances: These dissolve easily in water (e.g., salts, sugars).
Hydrophobic Substances: These do not dissolve in water (e.g., oils, fats).
Solution: A homogeneous mixture of solute and solvent.
Aqueous Solution: A solution in which water is the solvent.

Acids, Bases, and pH

The pH scale measures the concentration of hydrogen ions in a solution, affecting chemical reactions and biological processes.

pH: Defined as the negative logarithm of hydrogen ion concentration:
Neutral Solution: At 25°C, M and M, so .
Acid: Substance that increases ion concentration in solution (pH < 7). Examples: Hydrochloric acid (HCl), carbonic acid (CO2 dissolved in water).
Base: Substance that reduces ion concentration in solution (pH > 7) by accepting or releasing . Examples: Ammonia (NH3), sodium hydroxide (NaOH).
Buffer: Substance that maintains pH within a narrow range by releasing or absorbing ions. Examples: Carbonic acid/bicarbonate system in living cells.
Tenfold Change: Each unit change in pH represents a tenfold change in or concentration. Example: The difference between pH 3 and pH 6 is times.

Environmental Impact: Acid Rain and Ocean Acidification

Human activities can alter the chemistry of water in the environment, with significant consequences for ecosystems.

Acid Rain: Produced when burning fossil fuels releases sulfur and nitrogen oxides, which mix with water vapor to form sulfuric and nitric acids. Acid rain (pH < 5.6) damages forests and aquatic habitats.
Ocean Acidification: Occurs when CO2 dissolves in seawater, forming carbonic acid (), lowering ocean pH and reducing available calcium for marine organisms. This negatively impacts coral reefs and shell-forming species.

Term	Definition	Example/Application
Cohesion	Water molecules sticking to each other	Surface tension, water transport in plants
Adhesion	Water molecules sticking to other substances	Capillary action in plant vessels
Buffer	Maintains pH by releasing/absorbing	Carbonic acid/bicarbonate in blood
Acid Rain	Precipitation with pH < 5.6 due to pollutants	Forest damage, aquatic ecosystem harm
Ocean Acidification	Decrease in ocean pH from dissolved CO2	Coral bleaching, shell dissolution

Additional info: The notes have been expanded to include definitions, examples, and academic context for each property and environmental impact. Equations and table entries have been inferred and clarified for completeness.