Chapter 3: Water and Life

Vocabulary flashcards covering chemical bonding in water, emergent properties supporting life, solution concepts, and pH dynamic equilibrium based on Chapter 3.

Polar Covalent Bond (in Water)

A covalent bond within a water molecule where electrons are shared unequally because oxygen pulls electrons toward itself, creating partial negative charges ($\delta-$) on oxygen and partial positive charges ($\delta+$) on hydrogen.

Cohesion

The property of water where hydrogen bonds hold water molecules together, resulting in high surface tension.

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid, facilitated in water by cohesive hydrogen bonding.

Adhesion

An attraction between different substances, such as the interaction between water molecules and plant cell walls.

Water Transport in Plants

The movement of water and dissolved nutrients upward against gravity through two types of water-conducting cells, driven by cohesion and adhesion.

Specific Heat

The amount of heat that must be absorbed or lost for $1\,\text{g}$ of a substance to change its temperature by $1\,{^\circ}\text{C}$.

Specific Heat of Water

$1\,\text{cal}/(\text{g} \cdot {^\circ}\text{C})$, a high value that minimizes temperature fluctuations to permit life.

Specific Heat of Ethyl Alcohol

$0.6\,\text{cal}/(\text{g} \cdot {^\circ}\text{C})$.

Temperature Moderation by Water

The stabilization of climate and air temperatures, such as in coastal areas, achieved because water absorbs heat when hydrogen bonds break and releases heat when hydrogen bonds form.

Evaporation

The phase transformation of a substance from a liquid state to a gas state.

Heat of Vaporization

The quantity of heat required to evaporate $1\,\text{g}$ of a liquid ($580\,\text{cal}$ for water).

Evaporative Cooling

The process in which the remaining liquid surface cools as it evaporates because the water molecules with the greatest kinetic energy leave as gas.

Expansion Upon Freezing

The property of water where stable hydrogen bonds in ice keep molecules farther apart than in liquid water, making ice less dense so it floats and insulates aquatic life below.

Solvent

The dissolving agent of a solution.

Solute

The substance that is dissolved in a solution.

Aqueous Solution

A solution in which water acts as the solvent.

Hydration Shell

A sphere of water molecules that surrounds each individual ion when an ionic compound is dissolved in water.

Hydrophilic

Having an affinity for water.

Hydrophobic

Lacking an affinity for water, such as nonpolar oil molecules.

Extraterrestrial Water Evidence

Observations indicating the presence of water outside Earth, including dark streaks on Mars and evidence of water vapor on more than $800$ planets beyond the solar system.

Dissociation of Water

A reversible dynamic equilibrium reaction where water molecules dissociate into hydronium ions ($\text{H}_3\text{O}^+$) and hydroxide ions ($\text{OH}^-$).

Acid

A substance that increases the $\text{H}^+$ concentration of a solution, such as $\text{HCl}$ or $\text{H}_2\text{SO}_4$.

Base

A substance that reduces the $\text{H}^+$ concentration of a solution, such as $\text{NaOH}$.

pH Scale

A scale based on the negative logarithm of hydrogen ion concentration, defined as $\text{pH} = -\log[\text{H}^+]$, where neutral solutions have a pH of $7$ ($[\text{H}^+] = 10^{-7}\,\text{M}$), acidic solutions have pH $< 7$, and basic solutions have pH $> 7$.

Buffer

A substance that minimizes changes in the concentrations of $\text{H}^+$ and $\text{OH}^-$ in a solution, typically consisting of a weak acid and its corresponding base that combine reversibly with $\text{H}^+$ ions.