Solutions

Using Henry's Law
PROBLEM 15-1
If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25°(,
how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the
same temperature
1:1 Analyze the Problem
You are given the solubility of a gas at an initial pressure. The
temperature of the gas remains constant as the pressure changes.
Because decreasing pressure reduces a gas's solubility, less gas should
dissolve at the lower pressure. •
Known
S, = 0.85 giL
P, = 4.0 atm
P 2 =1.0 atm
EI Solve for the Unknown
Unknown
S2 = giL
Rearrange Henry's law to solve for 52'
S, S2 (P2)
Ii; = P 2
' S2 = S, Ii;
Substitute the known values into the equation and solve.
S2 =(0.859/L)(~:g=)
=0.21g/L
II Evaluate the Answer
The answer is correctly expressed to two significant figures. The
solubility decreased as expected. The pressure on the solution was reduced
from 4.0 atm to 1.0 atm, so the solubility should be reduced
to one-fourth its original value, which it is.
PROBLEMS
1. If 0.55 g of a gas dissolves in 1.0 L of water at 20.0 kPa of pressure,
how much will dissolve at 110.0 kPa of pressure
2. A gas has a solubility of 0.66 giL at 10.0 atm of pressure. What is the
pressure on a 1.0-L sample that contains 1.5 g of gas
Assessment
3. Describe the characteristics of a solution and identify
the various types.
4. How do intermolecular forces affect solvation
5. What is solubility Describe two factors that affect
solubility.
6. Thinking Critically If a seed crystal was added to
a supersaturated solution, how would you characterize
the resulting solution
7. Making and Using Graphs Use the infonnation in
Table 15-2 to graph the solubilities of aluminum
sulfate, lithium sulfate, and potassium sulfate at
O°C, 20°C, 60°C, and lOO°e. Which substance's
solubility is most affected by increasing temperature
15.1 What are solutions 461