FACTORS AFFECTING SOLUBILITY

Structure effects- Vitamins

Fat-soluble (nonpolar) Water-soluble (polar) hydrophilic ( ’s H2O)

hydrophobic (’s H2O)

Pressure Effects

As pressure increases, gas solubility…

INCREASES!

Henry’s Law

P=kC P= partial pressure of gaseous

solute above sol’n C= conc of dissolved gas k = const for specific sol’n

Henry’s Law

The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution

Henry’s Law Works best when: dilute sol’ns of gases do not dissociate with

solvent do not react with solvent

Try this...

The solubility of O2 is 2.2 x 10-4 M at 0oC and .10 atm. Calculate the solubility of O2 at 0oC and 0.35 atm.

Temperature Effects

As the temperature of a liquid increases, the ability for a solute to dissolve…

increases? SOMETIMES!

Temperature Effects

Most substances are more soluble at higher temps, but NOT ALL!

Na2SO4, Ce2(SO4)3

Temperature Effects

For gases… solubility goes DOWN as

temperature increases

Raoult’s Law

Raoult’s Law animation

An Experiment

Two beakers are placed in a sealed chamber. One has water and the other has salt water.

An Experiment

Eventually, the water beaker is empty and the salt water beaker has twice the water…

WHY?

The Reason

The vapor pressure of the water is greater than the vapor pressure of the salt water.

The Reason

The water tries to achieve equilibrium by evaporating.

The salt water tries to absorb the water.

Key Idea

The presence of a nonvolatile solute lowers the vapor pressure of a solvent.

Think about it…

The solute lowers the number of gas molecules that can reach the surface and turn to vapor.

Raoult’s Law

Psol’n = solventPosolvent

Psol’n=obs vp of sol’nsolvent= mol fract of solv

Posolvent=vp of pure solv

Raoult’s Law C3H8O3 is a nonvolatile liq. What

is the vp of a sol’n made by adding 164g of glyceryn to 338 mL of H2O at 39.8oC? The vp of pure H2O at 39.8oC is 54.74 torr and its density is 0.992 g/mL.

Multiple Ions?

When a substance breaks up into more than one ion, it essentially has twice the effect that it is supposed to have.

Such as... What is the vp of a sol’n made

by adding 52.9 g of CuCl2 to 800.0 mL of water at 52oC? The vp of water at 52.00C is 102.1 torr and its density is 0.987 g/mL.

Molar Mass? Mass of cmpd is dissolved in

a solvent and the vp of resulting sol’n is measured. This will give us # of moles.

g/mol is molar mass!

LOOK! At 29.6oC, H2O has a vp of 31.1

torr. A sol’n is prepared by adding 86.7 g of “Y” (nonvolatile, nonelectro) to 350.0 g H2O. The vp of sol’n is 28.6 torr. What is MM of Y?

But what if solute is volatile? It will contribute to the

vapor pressure of the system!

PTOT=APAo + BPB

o

PTOT=APAo + BPB

o

PTOT = Total vp

A, B=mol fraction A,B

Pao,Pb

o=partial pressures of A and B

Ideal Solution When a liquid-liquid solution

obey Raoult’s law When sol-sol, solv-solv and

sol-solv interactions are similiar

Negative deviation

If the solute has an affinity for the solvent (H-bond)

Obs vapor pressure will be less than expected

Negative deviation

Often when Hsol’n is large and neg

EX: acetone and water

Positive deviation

Solute-solvent interactions are weaker than the interactions in the pure liquids

higher vp then expected

Positive deviation

EX: polar ethanol and nonpolar hexane

Ideal Solution

Very similar molecules benzene and toluene

For you to do... The vp of pure hexane (C6H14) at

60.0oC is 573 torr. That of pure benzene (C6H6) at 60.0oC is 391 torr. What is the expected vp of a sol’n prepared by mixing 58.9g hexane and 44.0g benzene. (ideal sol’n)

Homework

P 544 47, 51, 55, 58