Ch 9 - Solutions Flashcards
What are solutions?
- homogeneous mixture composed for 2+ substances to form a single phase, generally a liquid phase
What happens in solvation (dissolution)?
- 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
What is hydration?
solvation in water
When are dissolutions endothermic/exothermic?
most are endothermic, except the dissolution of gas into liquid (exothermic)
What is the difference between solubility and saturation?
- 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
What are complex ions (coordination compounds) composed of?
metallic ions bonded to various neutral compounds and anions referred to as ligands
What does the formation of complex ions do and what does the process involve?
- 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
When is percent composition by mass used?
- (mass of solute/mass of solution) x 100%)
used for aqueous solutions and solid-in-solid interactions
What is the mole fraction (X) and when is it used?
- (Xa = moles of solute (A)/ total moles of all species)
used for calculating vapor pressure depression and partial pressures of gases in a system
What is molarity (M) and when is it used?
- (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
What is molality (m) and when is it used?
- (m= moles of solute/kilogram of solvent)
used for boiling point elevation and freezing point depression
What is normality and when is it used?
- (number of equivalents per liters of solution)
the molarity of the species of interest and is used for acid-base and oxidation-reduction reactions
What is the solubility product constant (Ksp)?
the equilibrium constant for a dissociation reaction
- first right out balanced equation
Ksp = [A^n+]^m[B^m-]^n
When are saturated solutions in equilibrium?
at that particular temperature
What does the comparison of the ion produce (IP) to Ksp determine?
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
Why does complex ion formation in solution increase the solubility of other salts containing the same ions?
because it uses up the products of those dissolution reactions, shifting the equilibrium to the right (the opposite of the common ion effect)
What is the formation (stability) constant (Kf)?
the equilibrium constant for complex formation
- its value is usually much greater than Ksp
How does the common ion effect affect solubility?
- 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
What are colligative properties?
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
What is Roult’s law?
- 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
How does vapor pressure depression explain boiling point elevation?
as the vapor pressure decreases, the temperature (energy) required to boil the liquid must be raised
What do freeze point depression and boiling point elevation depend on?
shifts in the phase equilibrium dependent on the molality of the solution
What does osmotic pressure (II) depend on and how is it calculated?
primarily dependent on the molarity of the solution
II = iMRT
What is the van’t Hoff factor (i) used for?
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
What are the 7 general solubility rules in aqueous solutions (first 2 most important)?
- 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
How can solubility of a compound be increaesed?
- 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
How do solutions and solvents related in dilute solutions?
in dilute solutions, the volume of the solution is approximately equal to the volume of the solvent used
What is dilution and how is it calculated?
- a solution is diluted when solvent is added to a solution of higher concentration to produce a solution of lower concentration
MiVi = MfVf
How is the boiling point elevation calculated?
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
How is the freezing point depression calculated?
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
How does the addition of solute particles affect the melting point of ice?
- melting point decreases with added solute
- solute particles interfere with lattice formation, the highly organized state in which solid molecules align themselves
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
- 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
What ion would have the most negative contribution to the entropy change in a solution?
that with the highest charge density (highest magnitude in charge) through hydration effect
What type of mixtures will have vapor pressures higher than predicted by Raoult’s law?
- 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
What can be concluded about a solution dissolving KCl becoming cooler in temperature while it dissolves?
- 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
How do you convert mOsm/L to mol/L?
multiply by 10^-3
What are the Ksp values for every sparingly soluble salt of general formula MX, MX2, and MX3?
- MX: Ksp = x^2
- MX2: Ksp = 4x^3
- MX3: Ksp = 27x^4
where x is the molar solubility (assuming no ion effect)
