Chemistry Reference
In-Depth Information
Figure 15.3
Crystallization of
a Solute from a Supersaturated
Solution Until the Solution Holds
No Excess Solute
As time passes, crystals grow from
the supersaturated solution.
(e) Is the solution saturated, unsaturated, or supersaturated?
(f) If the system is then carefully cooled back to
0°C,
and no crystals appear,
is the system homogeneous or heterogeneous?
(g) Is the solution saturated, unsaturated, or supersaturated?
Solution
(a) Only 119 g of sodium acetate will dissolve in 100 g of water at
(b) The system is heterogeneous—a mixture of the solution and the excess
solid.
(c) The solution part is saturated; it holds as much solute as it stably can
hold at
(d) When the system is heated to
0°C.
0°C.
100°C,
all 170 g of solute will dissolve,
and the system is homogeneous.
(e) The solution is saturated; it holds 170 g in 100 g of water, which is the
maximum it can hold stably
at this temperature.
(f) Homogeneous. Because no solute crystallizes, the system is still a solution.
(g) The solution is supersaturated because the 170 g of solute that it holds is
more than the 119 g that would be stable at this temperature. If a small
crystal of sodium acetate is added, the excess sodium acetate will
crystallize out (see Figure 15.3).
Practice Problem 15.2
(a) What would your answer to part (e) of Example 15.2 be if only 161 g of
sodium acetate had been used?
(b) What would your answer to part (d) be if 90.0 g of water had been used?
A solution of a gas in a liquid with which it does not react is a little dif-
ferent. At any given temperature, the solubility of the gas in the liquid is directly
proportional to the partial pressure of the gas. This statement is known as
Henry's law.
Mathematically,
Concentration of gas
kP
where
k
is the Henry's law constant. Thus, to specify a saturated solution of a
gas in a liquid, we must specify both the temperature and the partial pressure
of the gas.
