Water and Life (Chapter 3)

Vocabulary flashcards covering key terms and definitions related to water’s properties, its role as a solvent, and acid-base chemistry important for life.

Water

The biological medium on Earth; makes up 70–95% of many cells; abundant on Earth and essential for life; acts as the primary solvent.

Polar covalent bond

A covalent bond with unequal sharing of electrons, resulting in partial positive and negative charges.

Hydrogen bond

A weak attraction between a hydrogen atom attached to an electronegative atom (like O) and another electronegative atom; enables water’s unique properties.

Polarity

A property of a molecule where opposite ends have opposite charges, leading to hydrogen bonding in water.

Cohesion

Water molecules sticking to each other due to hydrogen bonding.

Adhesion

Water molecules sticking to other substances due to hydrogen bonding.

Surface tension

The cohesive forces at the surface of a liquid that make it behave as if the surface were covered with a stretched skin.

Specific heat

The 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

The amount of heat required to convert 1 g of a liquid to its gaseous state.

Evaporative cooling

Cooling that occurs as a liquid evaporates, removing heat from the surface.

Expansion upon freezing

Water expands when it freezes, causing ice to be less dense than liquid water.

Hydrophilic

Materials that dissolve in water due to polar or ionic regions capable of forming hydrogen bonds.

Hydrophobic

Materials that repel water, typically nonpolar substances.

Colloid

A stable suspension of fine particles in a liquid.

Solvent

The dissolving agent in a solution (commonly water in biological systems).

Solute

The substance dissolved in a solvent.

Aqueous solution

A solution in which water is the solvent.

Solution

A homogeneous mixture of two or more substances.

Molarity

The number of moles of solute per liter of solution.

Mole

6.02 × 10^23 representative particles; the amount of substance containing Avogadro’s number of entities.

Hydronium ion

H3O+; the protonated form of water (often represented as H+ in solutions).

Hydroxide ion

OH−; the negatively charged hydroxide found in basic solutions.

Acid

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

Base

A substance that decreases H+ concentration, often by accepting protons or producing OH−.

pH

A measure of how acidic or basic a solution is; pH = −log[H+]; at 25°C, [H+][OH−] = 10^−14.

Neutral

A solution that is neither acidic nor basic (pH around 7 at 25°C).

Buffer

A substance that resists changes in pH by buffering added acids or bases.

Dissociation of water

Autoionization of water into H+ and OH−; in pure water, [H+] = [OH−] = 10^−7 M at 25°C.

Ocean acidification

Increased CO2 from burning fossil fuels lowers ocean pH by forming carbonic acid, reducing carbonate ions needed for calcification.

Carbonic acid

H2CO3 formed when CO2 dissolves in water; a key species in ocean acidification.

Bicarbonate

HCO3−, a product of carbonic acid dissociation used in buffering the ocean’s pH.

Carbonate

CO3^2− ion; combines with calcium to form CaCO3 in calcifying organisms.

Dynamic equilibrium (in water)

Dissociation and recombination of water molecules occur at equal rates.

pH scale relationships

Acidic solutions have pH < 7; basic solutions pH > 7; each unit change represents a tenfold change in H+ concentration.

Astrobiology connection

Search for life focuses on planets with water; presence of water supports habitability.