Oceanography Chapter 7
precipitate
(1) A solid substance formed in an aqueous reaction. (2) The process by which a solute forms in and falls from a solution. The falling of water or ice from the atmosphere.
ionic bond
A chemical bond resulting from attraction between oppositely charged ions. These forces are said to be "electrostatic" in nature.
mixture
A close intermingling of different substances that still retain separate identities. The properties of a mixture are heterogeneous; they may vary within the mixture.
refractometer
A compact optical device that determines the salinity of a water sample by comparing the refractive index of the sample to the refractive index of water of known salinity.
excess volatiles
A compound found in the ocean and atmosphere in quantities greater than can be accounted for by the weathering of surface rock. Such compounds probably entered the atmosphere and ocean from deep crustal and upper mantle sources through volcanism.
buffer
A group of substances that tends to resist change in the pH of a solution by combining with free ions.
solution
A homogeneous substance made of two components, the solvent and the solute.
pH scale
A measure of the acidity or alkalinity of a solution; numerically, the negative logarithm of the concentration of hydrogen ions in an aqueous solution. A pH of 7 is neutral; lower numbers indicate acidity, and higher numbers indicate alkalinity.
chlorinity
A measure of the content of chloride, bromine, and iodide ions in seawater. We derive salinity from chlorinity by multiplying by 1.80655.
salinity
A measure of the dissolved solids in seawater, usually expressed in grams per kilogram or parts per thousand by weight. Standard seawater has a salinity of 35% at 0°C (32°F).
trace element
A minor constituent of seawater present in amounts of less than 1 part per million.
solvent
A substance able to dissolve other substances. See also solution.
solute
A substance dissolved in a solvent. See also solution.
base
A substance that combines with a hydrogen ion in solution.
acid
A substance that releases a hydrogen ion in solution.
ion
An atom (or small group of atoms) that becomes electrically charged by gaining or losing one or more electrons.
salinometer
An electronic device that determines salinity by measuring the electrical conductivity of a seawater sample.
conservative constituent
An element that occurs in constant proportion in seawater; for example, chlorine, sodium, and magnesium.
nonconservative constituent
An element whose proportion in seawater varies with time and place, depending on biological demand or chemical reactivity. An element with a short residence time; for example, iron, aluminum, silicon, trace nutrients, dissolved oxygen, and carbon dioxide.
alkaline
Basic. See also base.
chemical equilibrium
In seawater, the condition in which the proportion and amounts of dissolved salts per unit volume of ocean are nearly constant.
precipitation
Liquid or solid water that falls from the air and reaches the surface as rain, hail, or snowfall.
Forchhammer's principle
See principle of constant proportions.
saturation
State of a solution in which no more of the solute will dissolve in the solvent. The rate at which molecules of the solute are being dissolved equals the rate at which they are being precipitated from the solution.
residence time
The average length of time a dissolved substance spends in the ocean.
dissolution
The dissolving by water of minerals in rocks.
diffusion
The movement—driven by heat—of molecules from a region of high concentration to a region of low concentration.
principle of constant proportions
The proportions of major conservative elements in seawater remain nearly constant, though total salinity may change with location; also called Forchhammer's principle.
mixing time
The time necessary to mix a substance through the ocean, about 1,600 years.
colligative properties
Those characteristics of a solution that differ from those of pure water because of material held in solution.
