Water and Life — Chapter 3 Vocabulary

Key vocabulary terms and concise definitions covering water properties, bonds, pH, acids/bases, buffers, and related concepts from Chapter 3.

Water

A polar molecule essential for life; solvent with unique emergent properties due to hydrogen bonding.

Hydrogen bond

A weak attraction between a partially positive hydrogen atom of one molecule and a partially negative atom (usually oxygen) of a neighboring molecule.

Polar covalent bond

A covalent bond in which electrons are shared unequally, creating partial charges within the molecule (as in H2O).

Cohesion

Attraction between water molecules caused by hydrogen bonding, enabling water transport in plants.

Adhesion

Attraction between water molecules and other substances (e.g., plant cell walls).

Surface tension

The resistance of a liquid’s surface to breaking; high in water due to hydrogen bonding at the air–water interface.

Hydrophilic

Substances that have an affinity for water; water-loving and typically ionic or polar.

Hydrophobic

Substances that repel water; nonpolar and do not readily dissolve in water.

Solvent

The dissolving medium in a solution; in biology, water is the primary biological solvent.

Solute

The substance dissolved in a solvent.

Solution

A homogeneous mixture of solute dissolved in solvent.

Aqueous solution

A solution in which water is the solvent.

Hydration shell

A shell of water molecules surrounding a dissolved ion or polar molecule.

Electrolyte

A substance that dissociates into ions in water and conducts electricity.

Nonelectrolyte

A substance that dissolves in water but does not form ions and thus does not conduct electricity.

Salt

A compound formed from acids and bases that dissociates into ions in water.

Acid

A substance that increases the H+ concentration in solution by donating protons.

Base

A substance that reduces H+ concentration or increases OH−; accepts protons.

pH

A measure of acidity/basicity; pH = −log10[H+], 0–14 scale; 7 is neutral.

Buffer

A substance that minimizes changes in pH by releasing or absorbing H+ or OH−.

Ocean acidification

Decrease in ocean pH due to dissolution of CO2 forming carbonic acid, reducing carbonate availability.

Carbonic acid (H2CO3)

Formed when CO2 dissolves in water; dissociates to H+ and HCO3−.

Bicarbonate (HCO3−)

A major component of the carbonic acid–bicarbonate buffering system.

Carbonate (CO3^2−)

Formed from bicarbonate at higher pH; essential for calcification in marine organisms.

Specific heat

Amount of heat required to raise the temperature of 1 g of a substance by 1°C; for water, 1 cal/(g·°C).

Heat of vaporization

Heat required to convert 1 g of a liquid to gas at its boiling point.

Evaporative cooling

Cooling of a liquid’s surface as it evaporates, stabilizing temperatures (significant for water).

Ice floats

Ice is less dense than liquid water due to stable hydrogen bonding, causing ice to float.

Hydronium ion (H3O+)

Protonated water; H+ in water exists mainly as H3O+.,

Hydrogen ion (H+)

A proton; in water, associates with water to form H3O+.,

Hydroxide ion (OH−)

The negatively charged ion produced when water dissociates; base component in autoionization.

Hydration shell

Water molecules surrounding dissolved ions or polar molecules.

Molarity (M)

Moles of solute per liter of solution.

Calorie (cal) / Kilocalorie (kcal)

Unit of heat; 1 kcal = 1000 cal; used to express food energy (1 kcal = 1 food Calorie).

Solvent vs. Solute distinction

Solvent is the dissolving medium; solute is the substance dissolved in the solvent.

Solution types: Homogeneous vs. Heterogeneous

Homogeneous solutions have uniform composition; heterogeneous mixtures do not.

Electrolyte vs. Nonelectrolyte

Electrolytes form ions in water and conduct electricity; nonelectrolytes do not form ions.

Mixture

A combination of two or more substances that may be homogeneous or heterogeneous.

Dissociation of water (Kw)

Water autoionizes to H+ and OH−; at 25°C [H+][OH−] = 10^−14 and [H+] = [OH−] = 10^−7 M.