Water and Life - Summary

Water molecules are shaped like a wide V with each hydrogen attached to oxygen via a polar covalent bond.
Exhibit hydrogen bonding where hydrogen is attracted to oxygen on a nearby molecule.
Hydrogen bonds in liquid water form, break, and reform frequently.

Cohesion: Water molecules are attracted to each other through hydrogen bonds; supports water transport against gravity in plants.
Adhesion: Water is attracted to other types of molecules.
Surface Tension: Water molecules at the surface form hydrogen bonds, making it difficult to break through.
Moderation of Temperature:
- High specific heat: Water absorbs or releases a large amount of heat with only a slight temperature change.
- High heat of vaporization: The quantity of heat a liquid must absorb to convert 1 gram to gas; allows evaporative cooling.
Expansion Upon Freezing: Water becomes less dense in solid form; ice floats and insulates water below.
Versatility as a Solvent:
- Solutions are homogenous mixtures; water is a versatile solvent due to its polarity.
- Aqueous solutions use water as the solvent.
- Hydrophilic substances have an affinity for water (polar or ionic); hydrophobic substances do not (nonpolar).

A hydrogen atom shifts from one water molecule to another, forming hydronium ions $(H_3O^+)$ and hydroxide ions $(OH^-)$ .
Represented as $H^+$ .
Reaction is reversible and reaches dynamic equilibrium.
Acids increase $H^+$ concentration; bases reduce $H^+$ concentration.

In pure water, $\left[H^+\right] \left[OH^-\right] = 10^{-14}$ .
Neutral solution: $\left[H^+\right] = \left[OH^-\right] = 10^{-7}$ .
pH is the negative logarithm of the $H^+$ concentration: $pH = -\log[H^+]$ .
pH decreases as $H^+$ concentration increases.
Neutral solutions have a pH of 7; acidic solutions from 1 to 7; basic solutions from 7 to 14.
Buffers maintain a stable pH by accepting and donating hydrogen ions as needed.