Water Chemistry, Hydrogen Bonding, and pH Regulation

Vocabulary flashcards covering water properties, hydrogen bonding, thermodynamics, solution chemistry, and pH buffer systems based on lecture notes.

Hydrogen Bond

A weak charge-based bond formed between a partial positive hydrogen atom and a partial negative atom (such as oxygen or nitrogen), possessing approximately $1/20\text{th}$ the strength of a covalent bond.

Cohesion

The phenomenon where water molecules hold each other together due to hydrogen bonding.

Adhesion

The phenomenon where water molecules cling or adhere to other surfaces or cell walls.

Hydrophilic

Describing polar or charged molecules ('water loving') that easily interact with and dissolve in water.

Hydrophobic

Describing nonpolar molecules ('water fearing') that lack charge, do not dissolve in water, and prefer interacting with other nonpolar molecules.

Surfactant (DPPC)

A amphipathic molecule with a charged head and neutral tail that lines the inner water layer of alveoli, preventing alveolar collapse by blocking water cohesion.

Hydrocarbon

A nonpolar chain made entirely of carbon and hydrogen atoms with equal electron sharing, forming hydrophobic structures.

Solvent

A liquid medium capable of dissolving other molecules (solutes) due to its chemical properties.

Solute

A substance that is dissolved by a solvent in a solution.

Solution

A liquid mixture formed when a solute is completely dissolved into a solvent.

Hydration Sphere

A sphere or shell of polar water molecules that surrounds and isolates individual dissolved ions or polar molecules.

Dissociation

The process where water molecules actively strip individual ions or polar molecules away from their lattice or crystal structure into solution.

Thermal Energy

The total kinetic energy resulting from the movement of atoms within a body of matter.

Temperature

A measure representing the average kinetic energy of molecules within a body of matter.

Heat

The transfer of thermal energy passing from a warmer object to a cooler object.

Calorie

The amount of heat required to raise the temperature of $1\text{ }g$ of water by $1\text{ }^\text{o}C$.

Kilocalorie

The amount of heat required to raise the temperature of $1\text{ }kg$ of water by $1\text{ }^\text{o}C$.

Specific Heat

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

Heat of Vaporization

The quantity of heat a liquid must absorb for $1\text{ }g$ of it to convert from a liquid state to a gaseous state ($100\text{ }^\text{o}C$ for water).

Evaporative Cooling

The process where the highest kinetic energy molecules leave as gas, removing thermal energy and cooling the remaining liquid or surface.

Hydroxide Ion ($OH^-$)

A negatively charged molecule formed when a water molecule loses a hydrogen proton while retaining the electron.

Hydrogen Proton ($H^+$)

A freely floating hydrogen cation lacking an electron, whose concentration in a solution determines its acidity.

pH Scale

A logarithmic scale ranging from $0$ to $14$ that measures the concentration of free hydrogen protons ($H^+$) in a solution.

Acid

A substance that increases the concentration of free hydrogen protons ($H^+$) in a solution, lowering the pH below $7$.

Base

A substance that reduces the concentration of hydrogen protons ($H^+$) in a solution (often by producing $OH^-$ or soaking up $H^+$), raising the pH above $7$.

Strong Acid / Strong Base

An acid or base that completely dissociates in water, represented in chemical equations by a single-direction arrow.

Weak Acid / Weak Base

An acid or base that does not completely dissociate in water and participates in reversible reactions, represented by two-way arrows.

Buffer

A substance (typically a weak acid or weak base) that minimizes changes in $H^+$ and $OH^-$ concentrations to maintain pH stability.

Carbonic Acid ($H_2CO_3$)

A major reversible blood buffer that donates $H^+$ when blood pH rises and converts to bicarbonate ($HCO_3^-$) to accept $H^+$ when blood pH drops.