Chem Class - April 22, 2010

Ions in Solutions
- The formation of a solution depends on the ability of the solute to dissolve in the solvent
- Solvation is the interaction between solutes and solvents
- Ionic solids (salts) are cyrstals made up of ions
- Molecular solids are crystals made up of neutral molecules
- Dissolving ionic solutions produces ions in a process called disssociation (remember?)

Ionizaiton is the break up of a neutral molecule into charged particles
Examples:
1) FeCl3 (s) ----->Fe 3+ (aq) + 3 Cl -1 (aq)
2) Ag2O (s) -----> 2 Ag + (aq) = O 2- (aq)

3) Na3PO4(s) -----> 3 Na + (aq) + PO4 (aq)

4) (NH4)2SO4 (s) -----> 2NH4 + (aq) + SO4 2- (aq)

Determining concentrations is relatively easy.

Examples:

What is the [Cl-] in a solution of 0.50 M AgCl3?

AgCl3 -----> Ag + (aq) + 3Cl- (aq)
Cl = 3x as many moles = (0.5 M) x 3 = 1.5 M

What is the [NO3-] in a solution of 0.82 M Fe(NO3)2?
Fe(NO3)2 -----> Fe 2+ (aq) + 2 NO 3- (aq)
(0.82 M) x 2 = 1.64 M

What is the [Cr2O7 2-] and [K+] when 3.5 g of K2Cr2O7 dissolved in 40 mL of water?
K2CrO7 -----> CrO7 2- (aq) + 2K + (aq)
3.5 g x 1 mol/294.2 g = 0.0

Here is a video showing the dissociation of salt: