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CHEM1602 > Chapter 13: Solutions > Flashcards

Chapter 13: Solutions Flashcards

1
Q

Define solubility.

A

The solubility of a substance is the amount of the substance that will dissolve in a given amount of solvent.

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2
Q

When two gases are mixed, how does the potential energy change?

A

The potential energy remains unchanged. The tendency to mix is not related to potential energy but rather entropy.

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3
Q

Define entropy.

A

Entropy is a measure of energy randomization or energy dispersal in a system.

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4
Q

Why do two ideal gases mix?

A

The pervasive tendency for energy to spread out, or disperse, whoever it is not restrained from doing so is the reason two ideal gases mix.

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5
Q

What are the three interactions of intermolecular forces in a solution?

A
  1. The solvent and solute particles.
  2. The solvent particles themselves.
  3. The solute particles themselves.
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6
Q

In general, when does a solution form?

A

A solution forms when the solvent-solute interactions are comparable to or stronger than the solvent-solvent interactions and the solute-solute interactions.

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7
Q

What are the three enthalpy changes that occur with solution formation?

A
  1. Separating the solute into its constituent particles.
  2. Separating the solvent particles from each other to make room for the solute particles.
  3. Mixing the solute particles with the solvent particles.
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8
Q

Why is the first enthalpy change in solution formation positive?

A

Separating the solute into its constituent particles is always endothermic (+∆ H) because energy is required to overcome the forces that hold the solute particles together.

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9
Q

Why is the second enthalpy change in solution formation positive?

A

Separating the solvent particles from each other to make room for the solute particles is endothermic (+∆ H) because energy is required to overcome the intermolecular forces among the solvent particles.

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10
Q

Why is the third enthalpy change in solution formation negative?

A

Mixing the solute particles with the solvent particles is exothermic (-∆H) because energy is released as the solute particles interact (through intermolecular forces) with the solvent particles.

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11
Q

Define enthalpy of solution.

A

The enthalpy of solution is the sum of the changes in enthalpy for each step, according to Hess’s law.

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12
Q

What is molality?

A

A measure of concentration with the unit amount solute (mol) / mass solvent (kg).

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13
Q

Why is molarity sometimes not a good measure of concentration?

A

Molarity cannot tell you how much solvent there is. And because the volume of the solution changes with temperature, molarity is variable.

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14
Q

When solute is added to water, is the volume of the solution or the solvent greater?

A

The volume of the solution.

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15
Q

When solute is added to water, is molarity or molality greater?

A

Molality is greater than molarity.

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16
Q

When are the values for M and m closest?

A

The values are closest for dilute solutions.

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17
Q

Is the ∆H of a solid -> gas enthalpically favorable?

A

No; ∆H > 0

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18
Q

What type of configuration does enthalpy favor?

A

Enthalpy favors configurations with more or stronger intermolecular interactions (lower energy).

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19
Q

Why do gases mix?

A

Ideal gases do not interact with each other, so they cannot minimize their energy. Therefore, since systems prefer to be in a more disordered state according to the property of entropy, the gases mix.

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20
Q

Is the ∆S of a solid -> gas enthalpically favorable?

A

Yes; ∆S > 0.

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21
Q

Are there more or less solute-solute interactions after dissolution?

A

Less.

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22
Q

Are there more or less solute-solvent interactions after dissolution?

A

More.

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23
Q

Are there more or less solvent-solvent interactions after dissolution?

A

Less.

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24
Q

How is vapor pressure related to the strength of intermolecular forces?

A

Vapor pressure decreases as the strength of intermolecular forces increases.

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25
Q

How is boiling point related to the strength of intermolecular forces?

A

Boiling point increases as the strength of intermolecular forces increases.

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26
Q

How is ∆Hsolute related to ∆Hlattice? Why?

A

∆Hsolute = -∆Hlattice. ∆Hsolute represents the separation of the solute into atoms/ions. Lattice energy is the formation of an ionic solid from its constituent ions, which is the reverse of ∆Hsolute.

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27
Q

Is ∆Hsolvent endothermic or exothermic?

A

Endothermic because separating solvent molecules requires energy.

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28
Q

Is ∆Hmix endothermic or exothermic?

A

Exothermic because new interactions are created that are enthalpically favorable.

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29
Q

When does the property of miscibility apply?

A

The property of miscibility applies when mixing two liquids.

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30
Q

What two components make up ∆Hhydration?

A

∆Hsolvent and ∆Hmix.

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31
Q

What does it mean for a solution to be unsaturated?

A

The concentration of the solute in the solution can be increased by adding more solute.

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32
Q

What does it mean for a solution to be saturated?

A

The concentration of the solute cannot be increased by adding more solute.

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33
Q

What is dynamic equilibrium in the context of solutions?

A

The point at which the rate of dissolution = the rate of recrystallization.

34
Q

Define supersaturated solution.

A

A solution with more solute dissolved than is allowed.

35
Q

What is the general relationship between solubility and temperature?

A

Solubility generally increases with temperature.

36
Q

When a piston is moved down in a cylinder, what happens to the volume of the gas and the vapor pressure?

A

The volume of the gas decreases and the vapor pressure increases.

37
Q

When a piston is moved down in a cylinder, is the rate of vaporization or condensation greater? What net effect does this have?

A

The rate of condensation is greater. The effect is that the solute goes into the liquid.

38
Q

When vapor pressure increases as a result of a piston moving downwards in a cylinder, what is the effect on the solubility?

A

Solubility increases as vapor pressure increases.

39
Q

What is the relationship between vapor pressure and temperature? What is the effect of this relationship on solubility?

A

Vapor pressure increases as temperature increases. As a result, solubility decreases as temperature increases.

40
Q

Describe the process of reaching dynamic equilibrium in a sodium chloride solution.

A
  1. When NaCl is first added to water, sodium and chloride ions begin to dissolve into the water.
  2. As the solution becomes more concentrated, some of the sodium and chloride ions can begin to recrystallize as solid NaCl.
  3. When the rate of dissolution equals the rate of recrystallization, dynamic equilibrium has been reached.
41
Q

What is the relationship between the solubility of most solids in water and temperature?

A

Solubility increases with increasing temperature.

42
Q

How does the process of recrystallization purify a solid?

A

In this technique, enough solid is added to water (or some other solvent) to create a saturated solution at an elevated temperature. As the solution cools, it becomes supersaturated and the excess solid precipitates out of the solution. If the solution cools slowly, the solid forms crystals as it comes out of solution. The crystalline structure tends to exclude impurities, resulting in a purer solid.

43
Q

What two factors affect the solubility of a gas in a liquid?

A

Temperature and pressure.

44
Q

What is the relationship between the solubility of gases in liquids and temperature?

A

Unlike solids dissolved in liquids, solubility decreases with increasing temperature.

45
Q

What is the relationship of the solubility of gases in liquids and pressure?

A

The higher the pressure of a gas above a liquid, the more soluble the gas is in the liquid.

46
Q

Describe the response of a carbon dioxide and water solution contained in a cylinder when the volume decreases.

A

When the volume decreases, the pressure of carbon dioxide increases, causing the rate of molecules entering the solution to rise. The number of molecules in solution increases until equilibrium is established again. However, the amount of carbon dioxide in solution is now greater.

47
Q

What is Henry’s Law?

A

Henry’s Law says the the solubility of a gas (usually in M) is equal to the Henry’s Law constant x the partial pressure of the gas (usually in atm).

48
Q

What is the Henry’s Law constant dependent on?

A

kH is a constant of proportionality that depends on the specific solute and solvent and temperature.

49
Q

What relationship does Henry’s Law reveal?

A

The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid.

50
Q

How do you calculate mole fraction?

A

amount solute (in mol) / total amount of solute and solvent (in mol)

51
Q

How do you calculate mole percent (mol %)?

A

amount solute (in mol) / total amount of solute and solvent (in mol) x 100

52
Q

How do you calculate parts by mass?

A

mass solute / mass solution x multiplication factor

53
Q

What is the multiplication factor of percent by mass?

A

100%

54
Q

What is the multiplication factor of part per million (ppm)?

A

10^6 ppm

55
Q

What is the multiplication factor of parts per billion by mass (ppb)?

A

10^9 ppb

56
Q

How do you calculate parts by volume?

A

volume solute / volume solution x multiplication factor

57
Q

Why is molarity (M) a useful unit for making, diluting, and transferring solutions?

A

It specifies the amount of solute per unit of solution.

58
Q

Why does molarity vary with temperature?

A

Molarity depends on volume, and because volume varies with temperature, molarity also varies with temperature. For example, a 1 M aqueous solution at room temperature is slightly less than 1 M at an elevated temperature because the volume of the solution is greater at the elevated temperature.

59
Q

What is a colligative property?

A

A property that depends on the number of particles dissolved in solution, not the type of particle.

60
Q

What are the four colligative properties discussed?

A

Vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure.

61
Q

What is the effect of a nonvolatile nonelectrolyte solute on the vapor pressure of the liquid into which it dissolves?

A

The vapor pressure of the solution is lower than the vapor pressure of the pure solvent.

62
Q

What is Raoult’s law?

A

The vapor pressure of the solution = the mole fraction of the solvent x the vapor pressure of the pure solvent at the same temperature.

63
Q

How does an ideal solution behave?

A

It follows Rauolt’s law exactly. The solute-solvent interactions are similar in magnitude to the solute-solute and solvent-solvent interactions.

64
Q

How do strong solute-solvent forces affect the results of Raoult’s law?

A

Stronger solute-solvent forces mean particles are less likely to escape, resulting in a lower vapor pressure.

65
Q

How do weak solute-solvent forces affect the results of Raoult’s law?

A

Weak forces mean particles are more likely to escape, leading to higher vapor pressure.

66
Q

What two quantities must be equal for a liquid to boil?

A

Vapor pressure must equal atmospheric pressure.

67
Q

Why do non-volatile solutes lower the vapor pressure of a solvent?

A

A higher temperature is required to get the vapor pressure to equal atmospheric pressure.

68
Q

What effect does the presence of a solute in solution have on crystallization?

A

The solute prevents the solution from crystallizing, therefore lowering the temperature required to freeze (freezing point).

69
Q

Define osmosis.

A

Osmosis is the flow of solvent through a semipermeable membrane. These membranes only allow certain materials (solvent in our case) to pass through.

70
Q

What is osmotic pressure?

A

The pressure required to equalize liquid levels.

71
Q

What does the prefix “iso” mean?

A

Same.

72
Q

How is the van’t Hoff factor calculated?

A

i = mol of particles in solution / mol of formula units dissolved.

73
Q

What effect does ion pairing have on colligative properties?

A

It reduces the number of solute molecules/atoms/ions in solution, and the magnitude of change may not be as large as we expect.

74
Q

Why is the heat of hydration always exothermic (-)?

A

Because the ion-dipole interactions that occur between a dissolved ion and the surrounding water molecules are much stronger than the hydrogen bonds in water, ∆Hhydration is always large and negative for ionic compounds.

75
Q

When |∆Hsolute| < |∆Hhydration|, what happens?

A

The amount of energy required to separate the solute into its constituent ions is less than the energy given off when the ions are hydrated. ∆Hsolution is therefore negative and the solution process is exothermic. The solution feels warm to the touch.

76
Q

When |∆Hsolute| > |∆Hhydration|, what happens?

A

The amount of energy required to separate the solute into its constituent ions is greater than the energy given off when the ions are hydrated. ∆Hsolution is therefore positive, and the solution process is endothermic (if a solution forms at all). The solution feels cool to the touch.

77
Q

When |∆Hsolute| = |∆Hhydration|, what happens?

A

The amount of energy required to separate the solute into its constituent ions is roughly equal to the energy given off when the ions are hydrated. ∆Hsolution is therefore approximately zero, and the solution process is neither appreciably exothermic nor endothermic. There is no noticeable change in temperature.

78
Q

How does the solubility of gases depend on pressure?

A

The higher the pressure of a gas above a liquid, the more soluble the gas is in the. liquid.

79
Q

What does the Henry’s Law equation demonstrate?

A

It shows that the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid.

80
Q

If a beaker containing a pure solvent and a beaker containing a concentrated solution are placed in an enclosed area, what will happen?

A

The level of pure solvent drops and the level of solution rises. This is due to entropy’s tendency to mix and make concentrated solutions less concentrated.

81
Q

What is the effect of a nonvolatile solute in solution?

A

It lowers the vapor pressure of a solution, resulting in a lower freezing point and a higher boiling point.

82
Q

How are osmosis and vapor pressuring lowering similar?

A

In both cases, as a solution becomes concentrated, it develops a tendency to draw pure solvent to itself. In the case of vapor pressure lowering, the pure solvent is drawn from the gas phase. In the case of osmosis, the pure solvent is drawn from the liquid state. In both cases the solution becomes more dilute as it draws the pure solvent to itself.

CHEM1602 (8 decks)

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