Chapter 3: Water and Life

acid

A substance that increases the hydrogen ion concentration of a solution.

adhesion

The clinging of one substance to another, such as water to plant cell walls, in this case by means of hydrogen bonds.

aqueous solution

A solution in which water is the solvent.

base

A substance that reduces the hydrogen ion concentration of a solution.

buffer

A solution that contains a weak acid and its corresponding base. A buffer minimizes changes in pH when acids or bases are added to the solution.

calorie (cal)

The amount of heat energy required to raise the temperature of 1 g of water by 1°C; also the amount of heat energy that 1 g of water releases when it cools by 1°C. The Calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie.

cohesion

The linking together of like molecules, often by hydrogen bonds.

evaporative cooling

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state.

heat

Thermal energy in transfer from one body of matter to another.

heat of vaporization

The quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

hydration shell

The sphere of water molecules around a dissolved ion.

hydrogen ion

A single proton with a charge of 1+. The dissociation of a water molecule (H2O) leads to the generation of a hydroxide ion (OH−) and a hydrogen ion (H+); in water, H+ is not found alone but associates with a water molecule to form a hydronium ion.

hydronium ion

A water molecule that has an extra proton bound to it; H3O+, commonly represented as H+.

hydrophilic

Having an affinity for water.

hydrophobic

Having no affinity for water; tending to coalesce and form droplets in water.

hydroxide ion

A water molecule that has lost a proton; OH−.

joule (J)

A unit of energy: 1 J = 0.239 cal; 1 cal = 4.184 J.

kilocalorie (kcal)

A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1°C.

kinetic energy

The energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter.

molarity

A common measure of solute concentration, referring to the number of moles of solute per liter of solution.

mole (mol)

The number of grams of a substance that equals its molecular or atomic mass in daltons; a mole contains Avogadro's number of the molecules or atoms in question.

molecular mass

The sum of the masses of all the atoms in a molecule; sometimes called molecular weight.

ocean acidification

The process by which the pH of the ocean is lowered (made more acidic) when excess CO2 dissolves in seawater and forms carbonic acid (H2CO3).

pH

A measure of hydrogen ion concentration equal to −log[H+] and ranging in value from 0 to 14.

polar covalent bond

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.

polar molecule

A molecule (such as water) with an uneven distribution of charges in different regions of the molecule.

solute

A substance that is dissolved in a solution.

solution

A liquid that is a homogeneous mixture of two or more substances.

solvent

The dissolving agent of a solution. Water is the most versatile solvent known.

specific heat

The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1°C.

surface tension

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.

temperature

A measure in degrees of the average kinetic energy (thermal energy) of the atoms and molecules in a body of matter.

thermal energy

Kinetic energy due to the random motion of atoms and molecules; energy in its most random form.