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 affect solubility Concentration units Colligative properties

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 unsaturated If the max or more than the max has been added, solution is saturated Can 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)

Solubility If 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 ºC Ethanol: infinitely soluble in water Gases are infinitely soluble in one another

Trends and Control of Solubility For now, we are examining molecular compounds- not ionic compounds. General rules: 1. polar solutes dissolve in polar solvents 2. 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

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 do Proteins Fold?

Without lipids, you’d fall apart.

What holds DNA together?

DNA, H-Bonding, and Entropy

Introduction to Polymers Polymers are long molecules made of repeating units, called monomers. In general: Specific example:

Forces between polymer chains: Crosslinks Weak: Intermolecular force crosslinks Strong: Colvalent bond crosslinks

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?