16.1. Solubility http://www.ck12.org
FIGURE 16.6
MgF 2 →Mg^2 ++ 2 F−
Each unit of magnesium fluoride contains three ions (one Mg^2 +ion and two F−ions). Using the van’t Hoff factor to
describe this dissociation, we would say that i = 3, because three moles of ions are produced from the dissociation
of one mole of the ionic solid.
Gas Solutes
Gases are also capable of dissolving in liquids. There are many examples of this in our everyday lives. For example,
carbonated beverages contain dissolved carbon dioxide. We notice this when bubbles come out of solution when the
beverage is opened. Another example is when oxygen from the air we breathe dissolves in our blood, where it is
transported throughout the body. Fish and other aquatic organisms use gills to capture dissolved oxygen from their
environments.
Because determining the mass of a gaseous sample is generally less convenient than determining how many moles
are present, solubilities for gases are often expressed as concentrations instead of as the mass that can be dissolved
in a specified amount of solvent. A solution in which one mole of a gas is dissolved in one liter of solution has a
concentration of 1 molar (1 M). Because the solubility of most gases is much less than that, the molar solubility is
often given in millimolar (mM). A one millimolar solution contains 1/1000 mol of solute per liter of solution. Other
methods of expressing concentration, such as parts per million (ppm) or parts per billion (ppb), will be discussed in
the following lesson.
Example 16.6
What does it mean if the molar solubility of a gas is 2.0 mM?
Answer: