TIPS FOR THE TEACHER
Language ofChemistry
Concentration of terms

molarity (molar concentration) (M) moles of solute per liter of solution.
molality (molal concentration) (m) moles of solute per 1000 grams (1 kg) of solvent.
mole fraction (X 1 ) moles of component 1 divided by the total moles of all of the solution components (including the solvent).
percent by mass mass of solute divided by the total mass of all of the solution components (including the solvent).
percent mass to volume mass of the solute relative to the volume of solvent.
percent by volume volume of the solute divided by the total volume of the solution.
volume:volume the volume ratios of the solution components.
parts per million (ppm) number of mass units of the solute of interest relative to one million mass units of solution; e.g., micrograms per gram or milligrams per kilogram.

NOTE: The last five terms are not on a particle or mole basis for either solute or
solvent!
         Molality is moles per 1000 g of solvent whereas molarity is moles per
            1000 mL of solution.
         Mole fraction is the only concentration unit that is consistent from
            solvent to solvent.

solution types

A solution is a homogeneous mixture. Although solutions are often thought of in terms of liquid solvents, solutions can be solids in solids (alloys,
such as brass—zinc in copper), liquids in solids (mercury in zinc—referred to as zinc amalgam), gases in solids (hydrogen in palladium), solids in
liquids (salts in water), liquids in liquids (ethylene glycol or ethanol in water), gases in liquids (air in water), and gases in gases (air). Although
liquids and solids in gases are theoretically possible, if the particles are small enough to provide a homogeneous material in the gas, the material is effectively a gas itself.

colloids

Colloidal particles, which must be large enough to diffract or scatter light, can be either large single molecules (egg albumin, a protein of molar
mass about 43,000, or hemoglobin, the oxygen-carrier in your blood of molar mass about 68,000) or clusters of normally insoluble materials
(colloidal gold in water or dust in air).

            One of the most important aspects of this unit is solving solution concentration problems. Inasmuch as most textbooks have many solution concentration
            problems, none have been included other than those included with the laboratory and demonstration activities. Instilling the molarity concept is most
            important for reaction stoichiometry; however, selected problems using the other common concentration units (see Language of Chemistry) should also
            be included.
 

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