Solutions
Part 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