Solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent...
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Transcript of Solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent...
solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent under given conditions of T and P
saturated: soln is in eq. w/undissolved solute
unsaturated: more solute could dissolve
supersaturated: the amount of dissolved solute exceeds the solubility
--
--
soln has a clear, water-like appearance, butis VERY unstable
addition of a seed crystal causes excesssolute to crystallize, leaving a sat. soln. (w/visible solid)
i.e., there is solid at the bottom
i.e., soln is clear (MIGHT be colorless)
A supersaturated solution crystallizingupon the addition of a seed crystal. The
resulting solution is then saturated.
http://www.youtube.com/watch?v=HnSg2cl09PI
http://www.youtube.com/watch?feature=endscreen&v=yxi6nxAqyew&NR=1
T (oC)
So
lub
ility
(g/1
00 g
H2O
)supersaturated
unsaturated
Sol. Curve for a Typical SubstanceDissolved in a Liquid
saturation limit(i.e., solubility)
solid in liquid
gas in liquid
-- for solids, as T , sol. ___
-- for gases, as T , sol. ___
Factors Affecting Solubility
Solute-Solvent Interactions
-- As IMFs between solute and solvent increase, solubility _________.
miscible: describes pairs of liquids that mix in all proportions (v. immiscible)
increases
Methanol, which is used to fuel race cars,is miscible with water due to its highlypolar nature.
d– d–
d+d+
d+
Low molar mass alcohols are completely miscible inwater, due to H-bonding of hydroxyl group (–OH);as molar mass increases, the polarity of the alcoholmolecule... decreases (it behaves more like a purehydrocarbon) and miscibility decreases.
-- Substances with similar IMFs tend to be soluble in one another;
-- Some network solids aren’t soluble in either polar or non- polar solvents because of strong forces within the solid.
e.g., CH3OH vs. CH3CH2CH2CH2OH
“like dissolves like.” (pol/pol and np/np)
k = Henry’s law constant; it depends on solute, solvent, and temp. (M/pres. unit)
Pressure Effects
-- Pressure has no effect on the solubility of solids in liquids, but as P increases, gas solubility ___.
-- Henry’s law: Sg = k Pg
Sg = solubility of the gas in the solution (M)
Pg = partial pressure of the gas over the solution (pres. unit)
William Henry(1775 – 1836)
A bottled soft drink at 25oC has CO2 gas at a pressureof 5.0 atm over the liquid. If the partial pressure of CO2
in the atmosphere is 4.0 x 10–4 atm and the Henry’slaw constant for CO2 over water at 25oC is3.1 x 10–2 M/atm, calculate the solubility of the CO2
both before and after the bottle is opened.
BE
FO
RE
Sg = 3.1 x 10–2 M/atm (5.0 atm)
= 0.16 M (fresh)
AF
TE
R Sg = 3.1 x 10–2 M/atm (4.0 x 10–4 atm)
= 1.2 x 10–5 M (flat)
Sg = k Pg
Ways of Expressing Concentration
qualitative:
quantitative:
concentrated v. dilute
100 x solution of mass
component of mass % mass
x 106ppm =x 109ppb =x 1012ppt =
soln of mg/L 1 ppm 1
moles total
component of moles X fraction, mole
soln of liters
solute of moles M molarity,
solvent of kg
solute of moles m molality,
Unlike molarity, molality doesn’tchange with temp. because...mass remains constant w/changing T. (V changes w/T.)
To go between molarity andmolality, you need…the soln’s density.
A 5.5-g sample of well water contains 0.75 mg oflead ions. In ppm, find the concentration of lead ions.
610 x soln. of mass
comp. of mass ppm
66
10 x g 5.5
g10 x 0.75 ppm
= 0.14 ppm
The federal limit for lead indrinking water is 15 ppb.
140 ppb (!!!)
If a commercial bleach is 4.35% sodium hypochloriteby mass, calculate the bleach’s mole fraction andmolality of the sodium hypochlorite.
g 18.0
mol 1
g 74.5
mol 1= 0.05839 mol NaClO
= 5.3139 mol H2O
kg 0.09565
mol 0.05839 m
5.31390.05839
0.05839 X
= 0.610 m
= 0.0109
4.35 g NaClO
95.65 g H2O
100
gbl
each