ch 9 - Solutions Flashcards
solutions
homogeneous throughout - same phase. All of them are mixtures but not all mixtures are solutions
solute
dissolved or dispersed in a solvent
solvent
component of solution that remains in the same phase after mixing, in which solute is dissolved; if already in same phase as solute, the solvent is that which is present in greater quantity
Solvation
the electrostatic interaction between solute and solvent molecules; also called dissolution; when water is solvent called hydration
when solvation is exothermic
when new interactions between molecules are stronger than the original ones; favored at low temps
when solvation is endothermic
when the new interactions formed are weaker than the original ones; favored at high temps; most dissolutions are this
ideal solution
enthalpy of dissolution is equal to zero; solutions get close to this when overall strength of new interactions is approximately equal to overall strength of original interactions
entropy of dissolution
second property (along with enthalpy) that contributes to whether a dissolution is spontaneous or not - at constant temp and pressure, entropy always increases upon dissolution
solubility of a substance
the max amount of that substance that can be dissolved in a particular solvent at a given temp
saturated solution
when the max amount of solute has been added and the dissolved solute is in equilibrium with its undissolved state
if more solute is added to an already saturated solution
solute will not dissolve but precipitate to the bottom
dilute solution
solution in which proportion of solute to solvent is small ; still unsaturated
concentrated solution
solution in which proportion of solute to solvent is large; still unsaturated
when is a solute considered soluble
when Gibbs free energy is negative and reaction will proceed spontaneously
sparingly soluble salts
those solutes that dissolve minimally in a solvent (molar solubility under 0.1 M)
aqueous solution
solvent is water
hydronium ion
H3O+
solubility rules for aqueous solutions (know rules one and two)
- All salts containing ammonium (NH4)+ and alkali metal (group 1) cations are water-soluble; 2. all salts containing nitrate (NO3)- and acetate (CH3COO-) anions are water-soluble; 3. Halides (Cl-, Br-, I-) except fluorides, are water soluble except those formed with Ag+, Pb2+, and (Hg2)2+; 4. All salts of sulfate ion (SO4)2- are water soluble, except those formed with Ca2+, Sr2+, Ba2+, and Pb2+; 5. all metal oxides are insoluble except ones formed with alkali metals, ammonium, and CaO, SrO, and BaO; 6. all hydroxides are insoluble except ones formed with alkali metals, ammonium, and Ca2+, Sr2+, and Ba2+; 7. all carbonates (CO3)2+, phosphates (PO4)3-, sulfides S2-, and sulfites (SO3)2- are insoluble except ones formed with alkali metals and ammonium
complex ion - or coordination compound
refers to a molecule in which a cation is bonded to at least one electron pair donor (which could include the water molecule) [complexation reactions]
ligands
electron pair donor molecules
coordinate covalent bonds
bonds that hold complexes together, in which an electron pair donor (a Lewis base) and an electron pair acceptor (a Lewis acid) form very stable Lewis acid-base adducts
chelation
central cation of a complex is bonded to the same ligand in multiple places; usually requires large organic ligands that can double back to form second or third bond with the central cation
concentration
denotes the amount of solute dissolved in a solvent
percent composition by mass
mass of solute/mass of solution x 100
mole fraction (X)
XsubA = moles of A/total moles of all species; used to calculate the vapor pressure depression of a solution
molarity (M)
M = moles of solute/liters of solution
molality (m)
m = moles of solute/kilograms of solvent; for dilute aqueous solutions at 25 degrees C, the molality is approx equal to molarity because the density of water at this temp is 1 kg per L. situations where it is required are boiling point elevation and freezing point depression
normality (N)
equal to the number of equivalents of interest per liter of solution; equivalent is measure of the reactive capacity of a molecule (equal to a mole of the species of interest); how many moles of electrons an ion will accept in a certain solution
equation for concentration of solution after dilution
M sub i (V sub i) = M sub f (V sub f); M = molarity, V = volume and subscripts i and f = initial and final values
saturation point
in process of creating a solution, this is the equilibrium, where the solute concentration is at its max value for the given temp and pressure; rates of dissolution and precipitation are equal, and concentration of dissolved solute reaches a steady state (constant) value; neither is favored thermodynamically
reaction example that represents dissociation of such a solute in solution
A sub m (B sub m) ->
solubility product constant (K sub sp) for example formula A sub m B sub n
K sub sp = [A^(n+)]^m[B^(m-)]^n; where concentrations of ionic constituents are equilibrium (saturation) concentrations
Ion product (IP)
used to determine where the system is with respect to the equilibrium position; analogous to the reaction quotient, Q, for other chemical reactions: IP = [A^(n+)]^m[B^(m-)]^n; concentrations used here are the ionic constituents at that given moment in time, which may differ from equilibrium concentration
unsaturated solution
if a salt’s IP is less than the salt’s Ksp; dissolution is thermodynamically favored over precipitation
supersaturated solution
IP is greater than Ksp, solution is beyond equilibrium; thermodynamically unstable and any addition or further cooling will cause spontaneous precipitation (achieved by dissolving more solute and then cooling solution)
molar solubility
molarity of a solute in a saturated solution
common ion effect
the reduction in molar solubility that occurs to solubility of salt when it is dissolved in a solution that already contains one of its constituent ions
colligative properties
physical properties of solutions that are dependent on the concentration of dissolved particles but not on the chemical identity of the dissolved particles: vapor pressure depression, boiling point elevation, freezing point depression, osmotic pressure
Raoult’s law
accounts for vapor pressure depression caused by solutes in solution; as solute is added to a solvent, vapor pressure of the solvent decreases proportionately: P sub A = X sub A x P, degree sign, sub A; P sub A = vapor pressure of solvent A when solutes are present; X sub A = mole fraction of the solvent A in the solution; P, degree sign, sub A = vapor pressure of solvent A in its pure state
formula for which the boiling point of a solution is raised relative to that of the pure solvent
delta T sub b = iK sub b (m); delta T sub b = increase in boiling point; i = van’t Hoff factor; K sub b = proportionality constant characteristic of a particular solvent; m = molality of the solution
boiling point
temperature at which the vapor pressure of the liquid equals the ambient (incident) pressure; higher in solutions than pure solvents
Van’t Hoff factor
corresponds to the number of particles into which a compound dissociates in solution
causes of freezing point depression
presence of solute particles interferes with formation of lattice arrangement of solvent molecules associated with the solid state causing a need for a greater amount of energy to
formula for freezing point depression
delta T sub f = i(K sub f)m; delta T sub f = freezing point depression; i = van’t Hoff factor; K sub f = proportionality constant characteristic of a particular solvent; m = molality of solution
osmotic pressure
refers to a “sucking” pressure generated by solutions in which water is drawn into a solution: pi symbol = iMRT; where pi = osmotic pressure; i = van’t Hoff’s factor; M = molarity of the solution; R = ideal gas constant; T = temp
boiling point of water
100 C; 212 F, 273.2 K
ideal solutions
solutions that obey Raoult’s law which holds only when the attraction between the molecules of the different components of the mixture is equal to the attraction between the molecules of any one component in its pure state.
