AP Biology Unit 1: Chemistry of Life - Water Properties

Vocabulary flashcards covering chemical structure, physical properties, hydrogen bonding, pH calculations, and buffering mechanisms of water for AP Biology Unit 1.1.

Hydrogen Bond

A weak attraction between the partially negative oxygen atom of one water molecule and the partially positive hydrogen atom of a different water molecule or polar molecule.

Polarity of Water

The property of water resulting from single polar covalent bonds between oxygen and hydrogen, where oxygen's higher electronegativity creates a partial negative charge near oxygen and partial positive charges near hydrogen.

Cohesion

The attraction that causes water molecules to stick to other water molecules by hydrogen bonding.

Adhesion

The attraction that causes water molecules to stick to other polar molecules by hydrogen bonding.

Capillary Action in Xylem

The process by which water travels upward through narrow xylem vessels in plant stems, driven by cohesion among water molecules and adhesion to polar vessel walls.

Surface Tension

The property of water resulting from cohesive and adhesive forces among water molecules at the surface of the liquid due to hydrogen bonds.

High Specific Heat

The property of water requiring a large amount of energy to separate molecules during phase changes, allowing water to absorb or release large amounts of heat and stabilize climates.

Evaporative Cooling

The cooling mechanism that occurs when evaporating water absorbs heat energy from a body, enabled by water's high heat of vaporization.

Density Anomaly of Water

The physical property where solid water (ice) is less dense than liquid water because hydrogen bonding creates more space between water molecules in the solid state, allowing ice to float at $0\,^\circ\text{C}$.

Hydration Shell

The organized orientation of water molecules surrounding dissolved ions, where partially negative oxygen atoms face cations like $\text{Na}^+$ and partially positive hydrogen atoms face anions like $\text{Cl}^-$.

Hydrophilic

"Water-loving"; describes polar or ionic substances that readily interact with or dissolve in water.

Hydrophobic

"Water-fearing"; describes nonpolar molecules that do not dissolve in water and are forced to aggregate or take on specific shapes in an aqueous environment.

pH Scale

A logarithmic measurement of hydrogen ion concentration in a solution defined by $\text{pH} = -\log([H^+])$, where a change of $1$ unit represents a $10\times$ difference in $[H^+]$.

Acid

A substance that increases the relative concentration of $H^+$ ions in a solution, producing a pH value less than $7$.

Base

A substance that increases the relative concentration of $OH^-$ ions in a solution, producing a pH value greater than $7$.

Buffer

A chemical system that maintains constant pH levels in living cells by accepting hydrogen ions ($H^+$) when excess ions are present and donating hydrogen ions when they are depleted.

Carbonic Acid–Bicarbonate Buffering System

The primary blood plasma buffer system where respiration-derived $\text{CO}_2$ reacts with water to form carbonic acid ($\text{H}_2\text{CO}_3$), which dissociates into bicarbonate ions ($\text{HCO}_3^-$) and hydrogen ions ($\text{H}^+$).