1. Solutions
College Chemistry

2. Types of Solutions
Remember, a solution is a homogenous mixture of two or more substances
Saturated solution – contains the maximum number of solute that will dissolve in a solvent at a specific temperature
Supersaturate solution – contains more solute than is present in a saturated solution
Not stable
Eventually the extra solute will come out through crystallization as crystals
Unsaturated solution – contains less solute that is present in a saturated solution

3. Types of Solutions

4. Molecular View of the Solution Process
the intermolecular attractions that hold molecules together in liquids in solids is also responsible for the formation of solutions
The ease of solution formation depends on these three types of interactions:
1. solvent-solvent interaction
2. solute-solute interaction
3. solvent-solute interaction

5. Molecular View of the Solution Process
For simplicity, we can think of the solution process as happening in three distinct steps
1. separation of solvent molecules
2. separation of solute molecules
3. solvent and solute molecules mix
Process can be endothermic or exothermic
DHsoln = DH1 + DH2 + DH3

6. Molecular View of the Solution Process

7. Molecular View of the Solution Process
Solute-solvent interaction > solute-solute AND solvent-solvent
Reaction is favorable and exothermic
DHsoln < 0
Solute-solvent interaction < solute-solute AND solvent-solvent
Reaction isn’t favorable and is endothermic
DHsoln > 0

8. Molecular View of the Solution Process
So if particles are more attractive to each other than the solute-solvent, why does dissociation take place?
Two things govern dissociation
1. energy (exothermic is more favorable)
2. tendency towards disorder (entropy)
Molecules want to be in a state of disorder (solution), do not enjoy being in order (just solute or just solvent)

9. Predicting Solubility
BP Oil Spill
Predicting Solubility
“like dissolves like” help us determine what is soluble (or dissolves) in another molecule
non-polar solute will dissolve in non-polar solvents and polar solutes will dissolve in polar solvents
This is why oil (non-polar) and water (polar) will not mix
Also, compounds with similar intermolecular forces will be solubility in each other
Ex: CCl4 (carbon tetrachloride) and C6H6 (benzene) are both non-polar and have dispersion forces only  fairly soluble
Ex: alcohols (with –OH) dissolve in water

10. Predicting Solubility
Miscibility – ability of two liquids to be completely soluble in each other in all proportions
Immiscible – not soluble
Solubility rules allows us to determine what ionic compounds will dissolve in water
Generally, ionic compounds will dissolve in polar solvents and covalent compounds will dissolve only in nonpolar solvents
Covalent compounds lack a dipole moment and cannot effectively solvate an ionic compound (such as NaCl)
Solvation – process in which an ion or molecule is surrounded by solvent molecules in a specific manner

11. Solvation

12. Example 12.1 Predict the relative solubilities of the following cases:
(a) Bromine (Br2) in benzene (C6H6, m = 0 D) and in water (H2O, m = 1.87 D)
(b) KCl in carbon tetrachloride (CCl4, m = 0 D) and in liquid ammonia (NH3, m = 1.46 D)
(c) formaldehyde (CH2O) in carbon disulfide (CS2, m = 0 D) and in water

13. Example 12.1 Predict the relative solubilities of the following cases:
(a) Bromine (Br2) in benzene (C6H6, m = 0 D) and in water (H2O, m = 1.87 D)
Br2 is nonpolar as in benzene (dispersion forces), water is polar
Br2 should only dissolve in benzene
(b) KCl in carbon tetrachloride (CCl4, m = 0 D) and in liquid ammonia (NH3, m = 1.46 D)
KCl is ionic, more soluble in ammonia since it has a larger dipole
(c) formaldehyde (CH2O) in carbon disulfide (CS2, m = 0 D) and in water
Formaldehyde is polar, carbon disulfide is nonpolar, and water is polar
Formaldehyde can also hydrogen bond with water and it is more soluble in water