Barrons SAT Subject Test Chemistry, 13th Edition

summarized after the General Rules of Solubility found below. At this point, solid
solutes, like KClO 3 , will generally be found at the bottom of the container and

appear not to further dissolve. In reality, portions of the undissolved solute
continue to go into solution as previously dissolved solute particles re-crystallize.
This type of condition—when two opposing processes [like dissolving and
crystallization] equal each other in rate—is called an equilibrium state. At this
point the solution is holding the maximum amount of solute that it can contain and
is referred to as a saturated solution. If more water is added to a saturated
solution, then more solute can be dissolved into it. A solution that contains less

solute than a saturated solution is described as being unsaturated and the
container will show no undissolved solute.

PROBLEM USING THE SOLUBILITY CURVE:

A solution contains 20 grams of KClO 3 in 200 grams of H 2 O at 80°C. How many

more grams of KClO 3 can be dissolved to saturate the solution at 90°C?

Reading the graph at 90° and up to the graph line for KClO 3 , you find that

100 grams of H 2 O can dissolve 48 grams. Then 200 grams can hold (2 × 48)

grams or 96 grams. Therefore, 96 g − 20 g = 76 g KClO 3 can be added to the

solution.

TIP

You should be familiar with these general rules of the solubility of solids.

General Rules of Solubility

All nitrates, acetates, and chlorates are soluble.

All common compounds of sodium, potassium, and ammonium are

soluble.

All chlorides are soluble except those of silver, mercury(I), and lead.

(Lead chloride is noticeably soluble in hot water.)

All sulfates are soluble except those of lead, barium, strontium, and

calcium. (Calcium sulfate is slightly soluble.)

The normal carbonates, phosphates, silicates, and sulfides are insoluble

except those of sodium, potassium, and ammonium.