Chapter 12: Solutions and other complex forces

• 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 effect solubility

• Concentration units

• Colligative properties

Solutions

• 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

Trends and Control of Solubility

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 do Proteins Fold?

Without lipids, you’d fall apart.

What holds DNA together?

DNA, H-Bonding, and Entropy

Laundry!