Chapter 13: Control of Solubility

• Many of the forces we’ve talked about occur between ions/molecules in solutions

• Definition: A homogeneous mixture (only one phase)

• Examples: saltwater, tap water, gemstones, brass, air

• Made up of a solvent and a solute:Solvent: the substance present in the larger amount.

Solute: the other substance

• Dissolving depends on attractive forces and entropy

What we’ll cover:

• Definitions

• Control of Solubility

• Things that affect solubility

Part 1: Definitions

• There is a maximum amount of any solute that will dissolve in a given solvent

• If less than the maximum has been added, solution is unsaturatedIf the max or more than the max has been added, solution is saturatedCan also have Supersaturated solutions

• The concentration of a solution is the amount of solute that has been dissolved in a solvent.

• Many units of concentration:molarity (mol/L), weight % (g/g), ppm (mg/L)

SolubilityIf a solute will dissolve in a solvent, it is soluble.

Some solutes have limits,

some are infinitely soluble in a solvent.

Sugar: 200 g in 100 mL water at 20 ºCEthanol: infinitely soluble in waterGases are infinitely soluble in one another

Trends and Control of Solubility

General rules: 1. polar solutes dissolve in polar solvents2. nonpolar solutes dissolve in nonpolar solvents

“Like dissolves Like”

Oil and water don’t mix: is oil polar or nonpolar?

You try: which of these will dissolve in water?

CH3OH CH3CH3 NH3

For now, we are examining molecular compounds- not ionic compounds.

Hydrophilic

Hydrophobic

Which of these will not dissolve in water?

1 2 3

33% 33%33%

1. NH3

2. CH3CH3

3. CH3OH

Which of these is least soluble in water?

1 2 3

33% 33%33%

1. CH3OH

2. CH3CH2CH2OH

3. CH3CH2CH2CH2OH

Introduction to Thermodynamic Control of the World

Enthalpy, H: Stronger bonds/IMFs are favored over weak ones.

Entropy, S: Freedom of movement is favored over constrained states.

Trends and Control of Solubility and Mixing: Why do some

things mix and others do not?What controls Solubility:

Enthalpy (enthalpy of solution)

Negative if new forces are stronger than original forces

Entropy

Depends on the entropy change of both the water and the solute.

Effects of Polarity

Why don’t water and oil mix?

1 2

50%50%1. Enthalpy: Water wants to keep H-bonds

2. Entropy: Water won’t form constricted arrangements

Why do Proteins Fold?

Without lipids, you’d fall apart.

What holds DNA together?

DNA, H-Bonding, and Entropy

Introduction to PolymersPolymers are long molecules made of repeating units, called monomers.

In general:

Specific example:

Common Addition Polymers

Forces between polymer chains: Crosslinks

Weak: Intermolecular force crosslinks

Strong: Colvalentbond crosslinks

Polar Whites!

Laundry!

Part 2: External Control of Solubility

Temperature and Pressure

Predictions:

Will solubility increase or decrease with increasing temperature?

Will solubility of a gas increase or decrease with increasing pressure?

What is the solubility of O2 in grams per liter, given normal atmospheric conditions?

Henry’s Law Constants: when are they constant?

Which is greater, kH for O2 at 20 oC or O2 at 50 oC?

Which is greater, kH for O2 or kH for NH3?

Henry’s Law, Solubility, and my Diet Coke