solutions Flashcards
solute disolves into a
solvent
solvation
electrostatic interaction between solute and solvent
- involes the breaking of solute-solute interactions and breaking of solvent-solvent interactins and creating solute-solvent interactions
another name for solvation
dissolution
when water is the solvent dissolution is called
hydration
when new interactions are stronger than the old ones…
the solvation is exothermic (gives off heat- heat as a product) - le chatelier principle- so this type of reaction is favoured at low temps –> want more heat- want right sided rxn
lowering the temp ofa liquid in order for a gas to dissolve favours
solubility ( le chateiler priniciple) bc this is exothermic
endothermic dissolutions
the new interactions are weaker than the old ones - so solvation is endothermic and favoured at high temperatures
Co2 into water - type of solvation
exothermic bc there are very minimal intermolecular interactions between CO2, so the only old bonds to be broken are water ( bicarbonate and carbonic acid )
bicarbonate
C00- OH
carbonic acid
carboxylic group with an OH
if strength of new interactions is about equal to the old interactions
overall enthalpy change of the dissolution is zero
- this is an ideal solution formation -
ideal solution
a solution with a change in enthalpy of dissolution equal to zero
sponanetiy of dissolution
depends on both entropy and enthalpy (decrease in Gibbs free energy)
to determine enthalpy change of NaCl
- NaCl
- look at wat has to be broken apart and what has to form
- to break ionic NaCl and H-bonds between water–> needs energy= endothermic
- ion-dipole interactions need to form between water and NaCl–> exothermic ( but mag is slightly less than endothermic mag) = so overall this rxn is endothermic and favoured at high temps
to determine etropy change of NaCl
(number of energy microstates available to a system at a given time)
- when NaCl disolves in water, it breaks its uniform lattice structure, and becomes more disorganized- more microstates available - simply- they are free to move in more ways
- the water however, becomes more restricted
- overall thou, the increase from the NaCl is greater than the water, so overall there is a positive entropy change- energy is dispersed
gibbs of the dissolution of NaCl
delta G= delta H - T delta S
- since low endothermicity and high entropy change -> ends up being negative = spontaneous
solubility def
the max amount of solute that will dissolve in solventat a given temp
what is solubility a function of? and why?
thermodynamics.
- if delta G is negative= spntaneous= solute is soluble at the given temp
- if positive= not disolvable
hydronium ion
H3O+
protons are never found alone? T/F
true
- always bound to an electron donor (hydrogen carrier)
- Base donate electron pairs and hold onto H’s
- water is a base and can pick up an H and act as an electron donor
all salts containing ___ and _____ cations are water-soluble
NH4+ and alkali metal cations
all salts containing ___ and _____ anions are water-soluble
nitrate (NO3-) and acetate (CH3COO-)
all metals oxides are INSOLUABLE unless bounded with?
alkali metals, ammonium, CaO, SrO and BaO
all hydroxides (OH) are INSOLUBLE unless
alkali metals, ammonium, Ca, Sr, Ba ( same as for metal oxides)
All carbonates (CO3^2-), phosphates sulfides (S^2-) and sulphites (SO3^2-) are ________
insoluble, unless bound with alkali metals or ammonium
SO4^ 2- are?
soluble unless with ca, Sr, BA or Pb
halides are??
water-soluble, unless bound to Ag, Pb, or Hg
Main thing to know about solubility rules?
- all group 1 metals are soluble
2. all nitrate salts are soluble
complex ion def
same as a coordinate compound
- molecule in which a cation (H+) is bound to atleast one electron pair donor (H2O)
- the electron pair donor molecules are called ligands
- complexes are held together with coordinate covalent bonds
complexes are held together by?
coordinate covalent bonds
chelation
- when the cation in a complex is bound to the ligand in more than one place
- large organic ligands (electron donors) are needed and they double back onto the central cation
exampe of a complex ion
the iron in hemoglobin
- the iron is the cation and it can bind to different ligands (o2, Co2, Co)
on MCAT, concentration normally expressed as
- percent composition by mass
- mole fraction
- molarity
- molaLITY
- normality
% comp by mass
mass solute/ mass solvent x 100
mole fraction
mole of A/ total moles
the sum of the mole fractions in a system should always equal one
Molarity (M)
moles solute/ L solution
for dilute solutions, the volume of solution = volume of solvent
Molality (m)
moles of solute / Kg of SOLVENT
at 25 C, molality is equal to _______. why? (and for dilute solutions)
equal to molartiy! this is because the density of water at this temp is 1 Kg/L
- so the denometers are equivalent
- can only use for dilute solutions, bc as the concentration increases, density increases
Normality (N)
the number of interesting things per liter
- so if we are interested in electrons accepted and MnO4- has a Normality of 5N, this means that 1 mol of MnO4- has 5 things of interest (accepts 5 electrons)
1M = 5N
another thing to be catioous of, is that N depends on the enviroment - in acidic solution it accepts 5 (5N), but in alkaline it only accepts 1 (1N)
the concentration of a solution can be determined by what formula, when a volume of solvent is added to a solution
MiVi= MfVf
M is molarity
the equilibrium of solvation is called
the saturation point ( and this is the lowest energy state for a set of conditions )
- this is a dynamic equilibrium for which the rate os dissolution and precipitation are equal!
- the system will move spontaneously to this point and any movement away from this will be nonspontaneous
describe saturation and dynamic equilibrium
rate of precipitation and dissolution are equal! at this point, the change in free energy is zero (as is the case for all systems in equilibrium!)
first step when given solution equilibrium question
write out the balanced dissociation reaction for the ionic compound (break it into its little pieces)
- this is necessary for calculating solubility product constant, ion product and molar solubility
solubility product constant (Ksp)
(follows the law of mass action)
the equilibrium constant for its solubility in aqueous solution
Ksp= [ A^n+]^m [B^m-]^n
“the concentration of A to the lil charge on B times the concentration of B to the lil charge on A”
sparingly soluble salts
most of the MCAT questions
- ionic compounds that have low solubility in water
- example: AgCl
law of mass action
In chemistry, the law of mass action is the proposition that the rate of the chemical reaction is directly proportional to the product of the activities or concentrations of the reactants. It explains and predicts behaviors of solutions in dynamic equilibrium.
K= [C]^c [D]^d / [A]^a [B]^b
whats different about the law of mass action of solutions?
no denomenation bc pure solids and liquids dont count!
Ksp is ?
temperature dependent ( like all other equilibrium constants)
- -> increases with an increasing temp for non-gas and decreases for gas solutes
- -> greater for gases at higher pressures
a high Ksp means?
lots of products —> more soluble
ion product
analogous to Q- reaction quotient
- it has the same form as Ksp (no denomenator)
- difference is the concentrations are the concentrations used at a given moment in time- whihc may be different from equilibrium concentrations!
supersaturated
IP > Ksp
saturated
IP=Ksp
molar solubility
the molarity of a solute when a solution is saturated (or in dynamic equilibrium)
Molar solubility of Fe(OH)3 is X, what is the Ksp at the same temp and pressure?
MS= the amount of Fe(OH)3 that dissolves to make a saturated solution.
- balance dissosiation reaction FIRST ALWAYS!
Fe(OH)3 –> Fe + 3 OH
Ksp= [Fe] + [OH]^3
- as x amont of Fe(OH)3 dissociates it makes x of Fe and 3x of OH
plug these values into Ksp
Ksp= [x][3x]^3
given Ksp of CuBr, x, then in 3 g of CuBr are dissolved in 1L of solution will solution be saturated, unsat or super sat?
- FIRST- write out balanced dissociation rxn
- CuBr–> Cu + Br
Ksp= [Cu] [Br]
so Ksp= x^2
- therefore MS of Cu=Br=CuBr (the amount of each in a saturated solution is equivalent)
To answer this: we cant compare Ksp to IP, but could compare MS with Molarity of 3g in 1L solution (g–> mol then divide by 1L)
compare
what’s unique about the solubility of complex ions
when these form solubility increases! (we call it Kf ( the formation of the complex in solution)
- water solvates around the complex
- have very high Kf values
kf= [complex]/ [A] + [B]
so there is a denominator- bc (aq)
common ion effect
when salt is added to a solution that already contains one of its constituent ions (ITS OWN)
- the salt being added REDUCES its solubility
- reduces this salts molar solubility (less will dissociate- le Chatelier principle)
- BUT no effect on Ksp itself
- less dissociates but that’s bc there is already some ion in the water- it still settles at its normal Ksp
