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A Lile Extra RECAP AND SUMMARY
Unit 08 - Solutions
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Match the description in the first column with the term in the second column.
1
The concentration expression used when calculating freezing point depression. G
A colligative
2
The ratio 10g NaOH / (10g NaOH + 190 g H2O) is an example of this
concentration expression. F
B colloid
3
The amount of a solute present in a solution when it is saturated under the given
conditions. K
C Raoult’s law
4
The process of surrounding a solute by water molecules. E
D Henry’s law
5
The type of solution formed when an equilibrium exists between a solid solute
and its dissolved ions. J
E hydration
6
The condition of equilibrium when 0.003g/mL of CdCO3 is completely
dissolved at 25oC and the solubility of CdCO3 is 0.000448 g/mL. L
F mass percent
7
The condition of equilibrium when 0.00005g/mL of CdCO3 is completely
dissolved at 25oC and the solubility of CdCO3 is 0.000448 g/mL. N
G molality
8
The type of solution that can form in a mixture with water and particles of
approximately 500 nm. B
H osmosis
9
The name given to the scattering of light that occurs when a beam of light at
right angles to the line of sight. M
I osmotic pressure
10
When two solutions are connected by a semipermeable membrane and are
isotonic, they have the same physical property which has this name. I
J saturated
11
The process of solvent molecules passing through a semipermeable membrane
from a more dilute solution to a more concentrated one. H
K solubility
12
A property of a solution that depends on the numbers of solute and solvent
particles. A
L supersatrated
13
The vapor pressure of a mixture is lower than that of the pure solvent by a factor
equal to the mole fraction of the solvent. C
M Tyndall effect
14
A statement that the pressure of a gas over a solvent in which it is dissolved
depends on the solubility of the gas in the solvent. D
N unsaturated
Are the following statements true or false?
15. A solution contains 0.30 mg of sodium ion per liter of solution. This corresponds to a
concentration of sodium ion of 3.0 ppm. FALSE
16. Crystallization occurs more readily when a seed crystal is present. TRUE
17. The molal boiling-point elevation constant for carbon tetrachloride is 2.53oC/m. This means that
1m of nonvolatile solute particles in carbon tetrachloride will cause the solution to boil 2.53oC
higher than pure carbon tetrachloride. TRUE
18. The presence of ion pairs in a NaCl solution will cause a further increase in osmotic pressure. FAL
19. CH4 should have hydrophilic properties. FALSE
20. A CH3(CH2)20 group in a molecule should cause the molecule to be hydrophobic. TRUE
21. Water and CH3(CH2)7OH are both liquids and therefore miscible. FALSE
22. Dissolving solid NaCl in water increases the entropy of the system. TRUE
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A Lile Extra RECAP AND SUMMARY
Unit 08 - Solutions
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23.
24.
25.
26.
27.
Copper metal is miscible in water. FALSE
Hydrocarbons are immiscible in water. TRUE
A 0.50M solution of KCl and a 0.10M solution of solution are isotonic. FALSE
A hypotonic solution has an osmotic pressure that is higher than another solution. FALSE
A 0.20M NaCl solution is hypertonic with respect to a 0.20M CaCl2 solution. FALSE
A few final short answer questions . . .
28. The heat of solution of RbCl in water at 25oC is 16.7 kJ/mol. Given that the process is endothermic, how
can RbCl dissolve in H2O?
29. What are two significant advantages of using the concentration unit molality compared to using molarity?
When will the two terms have similar values for an aqueous solution?
30. Which acid should give a greater freezing-point depression, a 0.002m HF solution of a 0.002m HCl solution?
Explain.
31. The freezing-points for 0.01m solutions of Co(NH3)6Cl3, MgSO4, NH4Cl, and CH3COOH are 0.0643oC,
0.0308oC, 0.0358oC, and 0.0193oC, respectively. Kf for H2O is 1.86oC/m. Which compounds are strong
electrolytes and which are weak? Which compound forms the greatest number of ions in a 0.01m solution?
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A Lile Extra RECAP AND SUMMARY
Unit 08 - Solutions
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#28
The energy associated with the ion-water attractions is not sufficient to overcome the
endothermic energetics of solute and solvent particle separation. Another principle exists and
operates in this case: processes that lead to an increase in the entropy of a system favor
spontaneous processes. The dissolving of a highly ordered crystalline RbCl in water leads to
solvated ions that now are able to move. This results in a net increase in the number of
microstates/arrangements of molecules in the system and permits the dissociation process to
occur.
#29
The key difference between the two concentration units is denominator. Molarity is calculated
using a volume, which is temperature dependent. So molarity varies with temperature while
molality is independent of temperature. When an aqueous solution is very dilute, the mass of the
solute contributes very little to density; thus there is essentially no difference between the
number of kilograms and the number of liters.
#30
The freezing-point depression is proportional to the molality of the solution. The two acids have
the same molality, but HCl is a strong acid and ionizes 100% while HF is a weak acid and ionizes to
a very small extent. The number of solute particles produced in the ionization of HCl is greater
than the number of particles produced in the ionization of HF. This results in a greater freezingpoint depression for HCl.
#31
The ΔT lowering for a 0.01m weak electrolyte solution is approximately ΔTf = Kfm = (1.86oC/m)
(0.01m) = 0.0186oC. Only the 0.01m CH3COOH solution has a ΔTf approximately equal to
0.0186oC; it is the only weak electrolyte. The other salt solutions produce freezing-point
depressions significantly greater than that of acetic acid; thus they are all strong electrolytes.
Since the 0.01m solution of Co(NH3)6Cl3 produces the greatest ΔTf lowering the molality of all
species in the solution is the largest; it forms the greatest number of ions in solution.
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