Definitions--Aquatic
Chemistry
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- acidity
- The ability
to neutralize OH- ions. This may be due to mineral acids in the water,
and to hydrolysis of some metal ions
- alkalinity, phenolphthalein alkalinity,
total alkalinity
- The ability to neutralize H+ ions. High alkalinity
water often has a high pH and high dissolved solids. Alkalinity is primarily due
to carbonate, bicarbonate and carbon dioxide dissolved in the water. Phenolphthalein
alkalinity is named for the indicator used in the titration of the water with
acid. At the phenolphthalein endpoint, about pH 8, the carbonate content is converted
to bicarbonate. For total alkalinity, methyl orange is used, and the titration
is carried to a pH of 4.3, at which point both the carbonate and bicarbonate have
been titrated to CO2, or H2CO3, carbonic acid.
BOD
Biological Oxygen Demand-determined by saturating the water sample with oxygen,
and measuring the oxygen content after 5 days incubation. The BOD is the concentration
of oxygen used up. The sample may need to be inoculated with bacteria, if it does
not have a sufficient amount to begin with.
COD Chemical oxygen demand.
Water sample is oxidized by refluxing with acidic potassium dichromate. Remaining
dichromate is determined by titration. The amount of dichromate used up in the
reaction is converted into an equivalent amount of oxygen to obtain the COD.
- colloid
- Particles
suspended in a liquid, which are larger than molecular size but small enough to
be moved about by molecular collisions. These particles do not settle under gravity.
Their surface area is very large per gram, and the particles have a charge due
to ions sorbed on the surface. This charge prevents coagulation or clumping of
the particles and therefore, coagulation can be brought about by neutralizing
the charge.
- complex
- A central molecule surrounded by ligand
molecules attached by electrostatic attractions. They have a structure, but the
bonds are often weak enough that the ligands can be readily exchanged in solution.
- coordination number
- The number of ligands usually coordinated
to a central atom or ion
- coordination sphere
- The space around
a central molecule, atom, ion, which is filled by the ligand species.
- dipole
- A
molecule which has a definite separation between its center of positive charge
and center of negative charge. Such a molecule is said to be polar. A polar species
will be more attracted to a charged species than will a non-polar one.
- equilibrium
constant
- An expression involving the concentrations of reactants and products
involved in a reaction. This expression yields a constant value regardless of
the concentrations. The constant changes only with temperature.
- hardness,
temporary hardness
- Hardness is produced by calcium and magnesium in water.
These ions cause a precipitate with soap. Temporary hardness is caused by bicarbonate
and can be removed by boiling which converts the bicarbonate to carbon dioxide
and calcium carbonate.
- Henry's law
- The solubility of a gas in
a liquid can be calculated by Henry's law which states that the solubility of
the gas is proportional to the partial pressure of the gas in contact with the
liquid.
- hydration
- Water molecules are attracted to ions in water
solution and coordinate around the ions, forming a sphere of hydration.
- hydrogen
bond
- The hydrogen atoms in water are very positive, because the oxygen
atom strongly withdraws the electrons in the O-H bonds. The hydrogen atoms on
adjacent molecules are attracted to the oxygen atoms forming a bond which is stronger
than the usual polar attraction, but less strong than a typical covalent bond.
This accounts for the very high boiling point of water compared with other similar
weight molecules.
- inorganic carbon
- The carbon containing compounds
in water which are not organic compounds, carbonate and bicarbonate species promarily.
- ligand,
unidentate, bidentate
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- organometallic
- An organic compound
containing metal atoms
- partial pressure
- pressure a gas in a mixture
would exert if it was alone in the container. For example, the partial pressure
of oxygen in air at 1 atmosphere pressure is 0.2 atm, because oxygen is 20% of
the atmosphere.
- pH
- -log[H+] where [H+]
= concentration of H+in moles/liter
- polarity
- property
of a molecule which describes the difference in location of the center of positive
and center of negative charge on the molecule. A nonpolar compound has these centers
coinciding. As they become further apart, the molecule becomes more polar.
- speciation
- determination
of particular chemical forms of an element, rather than just the total element.
Metals may be speciated by oxidation state (Cr(VI) vs. Cr(III), for example,)
or by successively stronger extractions from a solid sample.
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