Lecture 5_190613 Flashcards
Solute
thing being dissolved
Solvent
thing doing the dissolving (often water)
Molarity
M = moles of solute / liters of solution
* volume of solution
density of H2O is 1.000 g/ml at 4˚C (temp H2O is most dense)
Molality
m = moles of solute / kgs of solvent
* mass of solvent
Percent by Weight to Volume
%(w/v) = grams of solute / 100 ml of solution
*see 6/13 lecture example in notes!
NOTE: mg% = mg of solute / 100 ml of solution
mg% = mg/dL
Percent by Weight to Weight
%(w/w) = grams of solute / 100 g of solution\
Parts Per Million
grams of solute / million grams of solution = mass fraction (1 ppm = 1 mg/L; liquids)
moles of solute / million moles of solution = mole fraction (gases)
1 equivalent (Eq)
= 1 mole of “reactivity”
Example:
1 mole of Na+ = 1 equivalent of Na+
1 mole of Ca++ = 2 equivalents of Ca++ (because it has +2 charge)
1 normal solution (N)
1 equivalent / 1 liter of solution
Osmolarity
sum of the molarities of all solutes in a solution
Example:
The osmolarity of a 1 M solution of NaCl is 2 Osm (Na = 1 and Cl = 1)
increased Osm = decreased concentration
Solubility
Maximum amount of solute that will dissolve in a solvent
mass / volume
Like dissolves like – polar solvents dissolve polar solutes. non-polar solvents dissolve non-polar solutes.
Example: solubility (in H2O) of CH4 is 23 mg/l, solubility (in H2O) of CH3F is 2.4 kg/l (~100,000 times more soluble)
Heat of solution
ΔHsoln = ΔHsolute + ΔHsolvent + Δhmix
ΔHsolute = energy to break up solute (usually > 0)
ΔHsolvent = energy to break up solvent (usually > 0) ΔHmix = energy back by new arrangement (usually < 0)
ΔHsoln = total energy change during dissolving of solute
> 0 needs energy (endothermic) – feels cold
< 0 gives off energy (exothermic) – feels hot
Examples:
Acid + water is very exothermic and generates lots of heat.
Dissolving ammonium chloride (NH4Cl) in water is endothermic and it can be used as a cold pack.
Henry’s Law (pressure & solubility)
The solubility of a specific gas can be stated as,
S = k_H * Pgas
Increased pressure causes more gas to dissolve into solution.
where S is solubility, k_H is Henry’s constant, Pgas is partial pressure for specific gas
*k_H is specific for each gas and is temperature dependent
Temperature & solubility
Increased temperature
1) usually increases solubility of liquids and solids, but
2) decreases solubility of gases
*warm H2O = increased gas in H2O = increased life
As more solute is dissolved in a solution, the physical properties of the solution change
1) vapor pressure decreases with increasing solute concentration
2) boiling point increases with increasing solute concentration
3) freezing point decreases with increasing solute concentration
4) osmotic pressure increases with increasing solute concentration
For (2) and (3), think “anti-freeze” in a car. Anti-freeze increases the boiling point, preventing boiling over in summer, and decreases freezing point, preventing coolant freezing in winter.
if (2) is true then (1) is true (THINK SHIFTING TO RIGHT OF PHASE DIAGRAM)
Vapor Pressure Raoult’s law
Ps = Χs * P˚s
Where Ps is the vapor pressure exerted by solute s, Χs is the mole fraction of s in the solution and P˚s is vapor pressure of pure s.
The vapor pressure of a solute in a solution depends on the concentration
Ptotal = Χs1 * P˚s1 + Χs2 * P˚s2 + Χs3 * P˚s3 + …
Any solute that has no vapor pressure (P˚ = 0) will cause a decrease in vapor pressure compared to a solution without it. This results in an increase in boiling point.
Osmotic Pressure
∏ = M * R * T
where ∏ is osmotic pressure, M is molar concentration, R is universal gas constant, and T is temperature (in Kelvin).
high concentration to low
Colloids vs Solutions
Colloids contain particles larger than molecules suspended in a solvent.
These large particles reflect light, while dissolved molecules don’t.
Miscible
2 liquids are miscible if theyare soluble in each other in all proportions.
