CHEM 1312 Chapter 10: Properties of Solutions

Molarity (M)

mol solute / L solution

Molality (m)

mol solute / kg solvent

Mole Fraction (χ)

mol component / total mol (all components)

solute

the substance BEING dissolved (lesser amount)

solvent

the substance doing the dissolving (greater amount)

solubility

the maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature (a solution at the limit is “saturated”)

Aqueous solution

a solution where water is the solvent

ΔH_solution

ΔH₁ (separate solute) +ΔH₂ (separate solvent) +ΔH₃ (solute-solvent attraction forms)

“like dissolves like”

solutes and solvents with similar IMFs dissolve well, because the energy trade between broken and formed attractions is favorable

Henry’s Law

C = k_H * P

gas solubility increases with increasing partial pressure

Temperature effect on solid solubility

generally increases with increasing temperature

Temperature effect on gas solubility

decreases with increasing temperature

Raoult’s Law

P_solution = χ_solvent * P°_solvent

Nonvolatile solute

a solute that doesn’t evaporate/contribute its own vapor pressure

Two volatile components

P_total = χ_AP°_A + χ_BP°_B

Dalton’s Law applied to Raoult’s Law

Colligative property

a property that depends on the number of dissolved particles, not their identity

ΔT_b (boiling point elevation)

i*K_b*m

ΔT_f (freezing point depression)

i*K_f*m

T_{b, solution}

T°_b+ΔT_b

T_{f, solution}

T°_f − ΔT_f

K_b/K_f

boiling-point-elevation/freezing point depression constant (solvent specific)

Osmosis

movement of solvent across a semi-permeable membrane from LOW to HIGH solute concentration

Osmotic pressure (Π)

iMRT

van’t Hoff factor (i)

number of particles one formula unit produces in solution upon dissociation

strong electrolyte

i ≈ number of ions in formula

nonelectrolyte

i=1 (doesn’t dissociate)

Ion pairing

temporary clumping of oppositely charged ions in solutions, causing actual i to be slightly less than ideal i