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