AP Biology 2.5 (Water)

Polar molecule

A molecule with an uneven distribution of charge, producing partially positive and partially negative regions.

Hydrogen bond

A weak attraction between a partially positive hydrogen and a nearby partially negative electronegative atom.

Cohesion

Attraction of molecules of the same substance; water sticking to water.

Adhesion

Attraction between different substances; water sticking to another surface.

Surface tension

Resistance of a liquid’s surface to being broken, caused by cohesion among surface molecules.

Kinetic energy

Energy of motion.

Thermal energy

Total kinetic energy of all molecules in a sample of matter.

Temperature

A measure of the average kinetic energy of molecules.

Heat

Thermal energy transferred from a warmer object to a cooler object.

Calorie

Amount of heat needed to raise 1 gram of water by 1°C.

Specific heat

Amount of heat needed to change the temperature of 1 gram of a substance by 1°C.

Heat of vaporization

Amount of heat needed to convert 1 gram of liquid into gas.

Vaporization / evaporation

Change from liquid to gas.

Evaporative cooling

Cooling that occurs when the highest-energy molecules evaporate from a liquid.

Solution

A uniform mixture of two or more substances.

Solvent

The dissolving agent in a solution.

Solute

A substance dissolved in a solvent.

Aqueous solution

A solution in which water is the solvent.

Hydration shell

The layer of water molecules surrounding a dissolved ion.

Hydrophilic

Having an affinity for water; usually ionic or polar.

Hydrophobic

Lacking an affinity for water; usually nonpolar.

Molecular mass

The sum of the masses of all atoms in a molecule.

Mole

An amount of substance containing (6.02 \times 10^{23}) particles.

Molarity

Concentration measured as moles of solute per liter of solution.

Hydrogen ion (H⁺)

A positively charged hydrogen particle; in water it is associated with water molecules.

Hydronium ion (H₃O⁺)

A water molecule that has gained an H⁺.

Hydroxide ion (OH⁻)

An ion formed when water loses an H⁺.

Acid

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

Base

A substance that decreases the hydrogen ion concentration of a solution, often by accepting H⁺ or releasing OH⁻.

Acidic solution

A solution with more H⁺ than OH⁻.

Basic solution

A solution with less H⁺ than OH⁻.

Neutral solution

A solution with equal concentrations of H⁺ and OH⁻.

pH

A logarithmic measure of hydrogen ion concentration; lower pH means more acidic.

Buffer

A substance or system that resists pH change by accepting or donating H⁺.

Ocean acidification

The lowering of ocean pH as dissolved carbon dioxide forms carbonic acid.

Calcification

The process of making calcium carbonate structures, such as shells and coral skeletons.