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MCAT General Chemistry > Ch 9 - Solutions > Flashcards

Ch 9 - Solutions Flashcards

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1
Q

What are solutions?

A
  • homogeneous mixture composed for 2+ substances to form a single phase, generally a liquid phase
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2
Q

What happens in solvation (dissolution)?

A
  • the breaking of intermolecular forces between solute particles between solvent particles, with formation of intermolecular forces between solute and solvent particles
  • in an aqueous solution, water is the solvent
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3
Q

What is hydration?

A

solvation in water

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4
Q

When are dissolutions endothermic/exothermic?

A

most are endothermic, except the dissolution of gas into liquid (exothermic)

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5
Q

What is the difference between solubility and saturation?

A
  • solubility: the maximum amount of a solute that can be dissolved in a given solvent at a given temperature; often expressed as molar solubility (the molarity of the solute at saturation)
  • saturation: maximum solubility of a compound at a given temperature; one cannot dissolve any more of the solute just be adding more at this temperature
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6
Q

What are complex ions (coordination compounds) composed of?

A

metallic ions bonded to various neutral compounds and anions referred to as ligands

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7
Q

What does the formation of complex ions do and what does the process involve?

A
  • it increases the solubility of otherwise insoluble ions (the opposite of the common ion effect)
  • involves electron pair donors and electron pair acceptors such as those seen in coordinate covalent bonding
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8
Q

When is percent composition by mass used?

A
  • (mass of solute/mass of solution) x 100%)

used for aqueous solutions and solid-in-solid interactions

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9
Q

What is the mole fraction (X) and when is it used?

A
  • (Xa = moles of solute (A)/ total moles of all species)

used for calculating vapor pressure depression and partial pressures of gases in a system

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10
Q

What is molarity (M) and when is it used?

A
  • (M = moles of solute/liters of solution)
    most common unit for concentration and is used for rate laws, the law of mass action, osmotic pressure, pH and pOH, and the Nernst equation
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11
Q

What is molality (m) and when is it used?

A
  • (m= moles of solute/kilogram of solvent)

used for boiling point elevation and freezing point depression

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12
Q

What is normality and when is it used?

A
  • (number of equivalents per liters of solution)

the molarity of the species of interest and is used for acid-base and oxidation-reduction reactions

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13
Q

What is the solubility product constant (Ksp)?

A

the equilibrium constant for a dissociation reaction
- first right out balanced equation
Ksp = [A^n+]^m[B^m-]^n

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14
Q

When are saturated solutions in equilibrium?

A

at that particular temperature

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15
Q

What does the comparison of the ion produce (IP) to Ksp determine?

A

the level of saturation and behavior of the solution

  • IP < Ksp: solution is unsaturated and if more solute is added, it will dissolve
  • IP = Ksp: solution is saturated (at equilibrium) and there will be no change in concentrations
  • IP > Ksp: solution is supersaturated and a precipitate will form
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16
Q

Why does complex ion formation in solution increase the solubility of other salts containing the same ions?

A

because it uses up the products of those dissolution reactions, shifting the equilibrium to the right (the opposite of the common ion effect)

17
Q

What is the formation (stability) constant (Kf)?

A

the equilibrium constant for complex formation

- its value is usually much greater than Ksp

18
Q

How does the common ion effect affect solubility?

A
  • decreases solubility of a compound in ia solution that already contains one of the ions in the compound
  • the presence of that ion in solution shifts the dissolution reaction to the left, decreasing its dissociation
19
Q

What are colligative properties?

A

physical properties of solutions that depend on the concentration of dissolved particles but not on their chemical identity
- ex. vapor pressure depression, boiling point elevation, freezing point depression, osmotic pressure

20
Q

What is Roult’s law?

A
  • ideal solution behavior is observed when solute-solute, solvent-solvent, and solute-solvent interactions are all very similar
  • the pressure of other solutes decreases the evaporation rate of a solvent without affecting its condensation rate, thus decreasing its vapor pressure
    Pa = XaPoa
21
Q

How does vapor pressure depression explain boiling point elevation?

A

as the vapor pressure decreases, the temperature (energy) required to boil the liquid must be raised

22
Q

What do freeze point depression and boiling point elevation depend on?

A

shifts in the phase equilibrium dependent on the molality of the solution

23
Q

What does osmotic pressure (II) depend on and how is it calculated?

A

primarily dependent on the molarity of the solution

II = iMRT

24
Q

What is the van’t Hoff factor (i) used for?

A

in freezing point depression, boiling point elevation, and osmotic pressure calculations for solutes that dissociate

  • the number of compounds in a solution
  • if a molecule does not dissociate into smaller components, can assume i = 1
25
Q

What are the 7 general solubility rules in aqueous solutions (first 2 most important)?

A
  • all NH4+ and group 1 cations are water soluble
  • all nitrate (NO3-) and acetate (CH3COO-) anions are water soluble
  • halides excluding fluoride (F-) are water soluble except when with Ag+, Pb2+, and Hg22+
  • all sulfates (SO42-) are water soluble except with Ca2+, Sr2+. Ba2+, and Pb2+
  • all metal oxides are insoluble except with alkali meals, ammonium, CaO, SrO, BaO
  • all hydroxides are insoluble except with alkali metals, ammonium, Ca2+, Sr2+, and Ba2+
  • all carbonates (CO32-), phosphates (PO43-) sulfides (s2-) and sulfites (SO32-) are insoluble except with alkali metals and ammonium
26
Q

How can solubility of a compound be increaesed?

A
  • solubility of solids can be increased by increasing temperature
  • solubility of gases can be increased by decreasing temperature or increasing the partial pressure of the gase above the solvent
27
Q

How do solutions and solvents related in dilute solutions?

A

in dilute solutions, the volume of the solution is approximately equal to the volume of the solvent used

28
Q

What is dilution and how is it calculated?

A
  • a solution is diluted when solvent is added to a solution of higher concentration to produce a solution of lower concentration
    MiVi = MfVf
29
Q

How is the boiling point elevation calculated?

A

delta Tb = iKbm
calculates the amount that the normal boiling point is raised, not the bp itself
Tb is the increase in bp
i is van’t hoff factor (# of compounds in solution)
Kb is proportional constant
m is the molality

30
Q

How is the freezing point depression calculated?

A

delta Tf = iKfm
calculates the amount that the normal freezing point is decreased, not the freezing point itself
Tf is the decrease in freezing point
i is van’t hoff factor (# of compounds in solution)
Kf is proportional constant
m is the molality

31
Q

How does the addition of solute particles affect the melting point of ice?

A
  • melting point decreases with added solute
  • solute particles interfere with lattice formation, the highly organized state in which solid molecules align themselves
32
Q

Which processes are endothermic v exothermic:

  • breaking the solute into its individual components
  • making room for the solute in the solvent by overcoming intermolecular forces in the solvent
  • allowing solute-solvent interactions to occur to form the solution
A
  • endothermic because energy is required to break molecules apart
  • endothermic because the intermolecular forces in the solvent must be overcome to allow incorporation of solute particles
  • exothermic because polar water molecules will interact with the dissolved ions, creating stable solution and releasing energy
33
Q

What ion would have the most negative contribution to the entropy change in a solution?

A

that with the highest charge density (highest magnitude in charge) through hydration effect

34
Q

What type of mixtures will have vapor pressures higher than predicted by Raoult’s law?

A
  • those with strong solvent-solvent and solute-solute interactions than solvent-solute interactions
  • particles do not want to stay in solution and more readily evaporate, creating a higher vapor pressure than an ideal solution
35
Q

What can be concluded about a solution dissolving KCl becoming cooler in temperature while it dissolves?

A
  • dissolution is governed by enthalpy and entropy, which are related by deltaG = deltaH = TdeltaS
  • the cooling of the solution indicates that heat is used up in this bond breaking reaction meaning the dissolution is endothermic and H is positive
  • reaction is occurring spontaneously meaning G is negative, so the the only way G can be negative while H is positive is if S is large enough positively
  • the only way the solid can dissolve is if the increase in entropy is great enough to overcome the increase in enthalpy
36
Q

How do you convert mOsm/L to mol/L?

A

multiply by 10^-3

37
Q

What are the Ksp values for every sparingly soluble salt of general formula MX, MX2, and MX3?

A
  • MX: Ksp = x^2
  • MX2: Ksp = 4x^3
  • MX3: Ksp = 27x^4
    where x is the molar solubility (assuming no ion effect)

MCAT General Chemistry (12 decks)

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