Water and its Properties

Polarity of water molecule

The polarity of the water molecule and its resulting hydrogen bonding make water a unique substance with special properties

Homeostasis

Understanding water's special properties helps to elucidate its importance in maintaining homeostasis

Water polarity creates charges

Water's polarity creates a slightly positive charge on hydrogen atoms and a slightly negative charge on oxygen atom

Partial charges in water

Water generates partial charges (δ+ and δ-) because oxygen is more electronegative than hydrogen

Electronegativity difference

Oxygen nucleus attracts shared electrons more strongly than hydrogen nucleus, creating partial negative charge near oxygen

Hydrophilic substance

A polar or charged substance that interacts with or dissolves in water

Hydrophobic substance

A nonpolar substance that does NOT interact with or dissolve in water

Ice less dense than water - biological importance

Ice floats, insulating water below and allowing aquatic life to survive in winter

High heat capacity - biological importance

Helps organisms maintain stable internal temperatures; prevents rapid temperature changes in cells

High heat of vaporization

Hydrogen bonds need to be broken in order for water to evaporate; enables evaporative cooling (sweating)

Water as a good solvent

Water's polarity allows it to dissolve ions and polar molecules; enables chemical reactions in cells

Cohesion - biological importance

Water molecules stick together via hydrogen bonds; enables water transport in plants and creates surface tension

Surface tension

Result of cohesion at water surface; allows small organisms to walk on water and supports surface-dwelling life

Adhesion

Water is attracted to other molecules; helps water move up plant xylem against gravity

Acid

A substance that increases hydronium ion (H+) concentration in a solution

Base

Provides either hydroxide ions (OH-) or other negatively charged ions that combine with hydrogen ions, reducing their concentration

pH

A value that indicates a solution's acidity or alkalinity

pH 0 (strong acid)

[H+] = 10^(-1) M = 1 M (high [H+], strong acid)

pH 14 (strong base)

[H+] = 10^(-14) M = 0.00000000000001 M (low [H+], strong base)

Buffer

Compound that readily absorbs excess H+ or OH-, keeping the body's pH carefully maintained in narrow range