SolutionsPart I: The Solution Process

Solution:

Solutions:

Solute:

Solvent

Types of Solutions

The solution process To dissolve a solute in

a solvent, the intermolecular attractions between solute and solute must be strong enough to compete with solvent-solvent and solute-solute attractions.

Solvation

Hydration

Dissolving an ionic solid in water The ion-dipole

attractions between the salt and the solvent must be strong enough to overcome the lattice energy

“Steps” of the solution process

Step 1

“Steps” of the solution process

Step 1

Step 2

“Steps” of the solution process

Step 1

Step 2

Step 3

Endothermic vs. exothermic?

Why do processes occur? Achieve a lower energy state

Exothermic processes lead to lower enthalpy

Why do processes occur? More randomness

Greater “entropy” Can more than

compensate for increasing enthalpy

Did it dissolve, or did it react? Just because a substance “disappears” into a

solvent doesn’t mean that the substance dissolved!

Dissolving vs. reaction Dissolving

Physical change Can recover the original substance by evaporating the

solvent

Dissolving vs. reaction Dissolving

Physical change Can recover the original substance by evaporating the

solvent

Chemical change New substances form

Solutions saturated unsaturated

Supersaturated solutions

Will this substance dissolve?

“Like dissolves like” Non-polar substances tend to dissolve in

non-polar solvents

“Like dissolves like” Non-polar substances tend to dissolve in

non-polar solvents Polar substances tend to dissolve in polar

solvents.

“Like dissolves like” It comes down to

having similar intermolecular attractions.

Gases in solution Solubility depends on

intermolecular attractions

Gases in solution Solubility depends on

intermolecular attractions London forces

As molar mass increases, dispersion forces are stronger

Henry’s Law The solubility of a gas

in a liquid is directly dependent on the gas pressure

Henry’s Law The solubility of a gas

in a liquid is directly dependent on the gas pressure

Pressure really doesn’t affect solubility of solids and liquids

Henry’s Law Sg = kPg

Solubility and temperature Usually, solubility of

ionic solids increases with temperature

Gas solubility and temperature Solubility of gases

typically decreases with increasing temperature