TIPS FOR THE TEACHER
Boiling point temperature - at which the vapor pressure of a liquid is equal to
the external pressure.
Boiling point elevation - a colligative property in which the boiling point of a
solution is raised above that of the pure solvent according to the number of
solute particles present.
Buffer - a solution that resists change in pH when either OH – or H + is added.
Chlorinity - the total amount of dissolved halide ions (Cl – , F – , Br – ,I – ) present
in a solution such as seawater; usually expressed in molL –1 , ppt or ppm.
Colligative properties - physical properties of a solution (vapor pressure
lowering, boiling point elevation, freezing point depression, osmotic pressure)
that are different for a solution than for a pure solvent, according to the
number of solute particles, and not their identities.
Freezing point - the temperature where the solid and liquid phase of a substance
coexist; also called melting point.
Freezing point depression - a colligative property in which the freezing point
of a solution is lowered below that of the pure solvent according to the
number of solute particles present.
Melting point - see freezing point.
Osmosis - the flow of solvent into a solution through a semi-permeable membrane.
Osmotic pressure - a colligative property-the pressure which must be applied
to a solution to stop osmosis.
Parts per billion (ppb) - a unit of concentration. One ppb is one part of solute
per billion parts of solution. For example, if an air sample contained 1 ppb Hg
vapor then there is 1mL Hg(g) in 10 9 mL air or 1mL Hg in 10 6 L of air.
parts per million (ppm) one ppm is one part of solute per million parts of solution.
Parts per thousand (ppt) - one ppt is one part of solute per thousand parts of solution.
Salinity - total concentration of dissolved material (all ions), usually expressed
in molL –1 or ppt.
Gold can be mined from seawater. While seawater does contain a small amount of
gold (0.011 ppb), it is not economically feasible to separate it. Have students calculate
how much gold there is in the oceans, which contain approximately 3 x 10 19 L of water
(see Counterintuitive Examples).
1. How well must sewage be treated before dumping in the ocean? Need it be
pure water when it leaves the wastewater treatment plant or is some amount
of dissolved material more ecologically sound?
2. Effect of global warming on the ocean. As scientists worry about increasing
CO 2 and CH 4 concentrations in the atmosphere, what are the possible
effects on the ocean?
3. Additional CO 2 in the atmosphere can lead to greater quantities dissolved
in seawater. What effects might occur?
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