Chapter 14: Solutions 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

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 unsaturated If the max or more than the max has been added, solution is saturated 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 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? CH 3 OH CH 3 CH 3 NH 3

Trends and Control of Solubility What controls Solubility: Enthalpy (enthalpy of solution) negative if new forces are stronger than original forces Entropy more complicated

“Forcing” Solubility How do you make something dissolve if it is normally insoluble in a solvent? Grease and grime are made up of nonpolar compounds. Will they dissolve in water? They will dissolve in nonpolar solvents, like turpentine, gasoline. Good for cleaning hands? Soap: the substance that makes nonpolar compounds dissolve in water. How would you design a soap molecule? What chemical properties should it have?

Soap and Detergent Soap is both polar and nonpolar Attracted to water (polar) and grime (nonpolar) Soap is the salt of a fatty acid, it is a surfactant molecule. hydrophobic end hydrophilic end

Soap Soap is both polar and nonpolar Attracted to water (polar) and grime (nonpolar) Made from fats, which contain 3 fatty acids and glycerol

Soap Nonpolar end is attracted to grime Polar end is attracted to water Dirt is picked up off clothes, skin, and rinsed away See: Soap movie

Soap Hard water and soap Hard water contains high concentration of Ca 2+ and Mg 2+ ions Ion-ion forces between Ca 2+, Mg 2+ and soap anion results in soap scum (soap forms a solid compound on your skin, bathtub, etc.) Water softeners replace Ca 2+, Mg 2+ with Na + How does dry-cleaning work? Previously used CCl 4, now less carcinogenic solvents

Fabric Softener: Cationic Surfactants What effect will softener use have on absorptivity? without with

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

Cotton Cellulose polymer Absorbs water. Cellulose chains crosslinked by H-bonding.

Wrinkling

Chemical crosslinking agent. Permanent Press Cotton