Solutions

Question 1

Concentrations

Answer 1

• Percent Composition by Mass: (mass of solute / mass of solution) × 100%.
• Mole Fraction: Xᴀ = moles of gas A / total moles of all species.
• Molarity: M = moles of solute / liters of solution.
• Molality: m = moles of solute / kg of solvent.
• Normality: N = M × n, where the normality of a solution is equal to the number of equivalents of interest per liter solution.

Question 2

Dilution

Answer 2

• M(i) V(i) = M(f) V(f)

Question 3

Solubility Product Constants

Answer 3

• For rxn: AₘBₙ -> mA + nB.
• Kₛₚ = [A+]ᵐ [B-]ⁿ.
• Ion Product (IP) is analogous to Q.
• No denominator, as solids and liquids are not included.
• Solubility product constants, like all other equilibrium constants, are temperature dependent.
• IP < Kₛₚ, solution is Unsaturated and solute will continue to dissolve.
• IP = Kₛₚ, solution is Saturated and at equilibrium.
• IP > Kₛₚ, solution is Supersaturated and solute will precipitate out.
• For salt MX, Kₛₚ = (x)(x) = x².
• For salt MX₂, Kₛₚ = (x)(2x)² = 4x³.

Question 4

Common Ion Effect

Answer 4

• The solubility of a salt is considerably reduced when it is dissolved in a solution that already contains one of its constituent ions as compared to its solubility in a pure solvent.

• If X moles of AB(s) can be dissolved in 1 L of solution to reach saturation, then the molar solubility of AB(s) is X molar.
• The presence of the common ion results in a reduction in the molar solubility of the salt, however the value of the solubility product constant is not changed.
• The common ion effects results in the system reforming more of the solid salt via Le Chatelier’s principle.

Question 5

Vapor Pressure Depression

Answer 5

• Vapor pressure of the solvent decreases as solute concentration increases.
• Raoult’s Law: Pᴀ = Xᴀ Pᴀ°, where Pᴀ is vapor pressure of solvent A when solutes are present, Xᴀ is mole fraction of solvent A in solution, and Pᴀ° is vapor pressure of solvent A in its pure state.
• Xᴀ = mol solvent / total mol.

Question 6

Boiling Point Elevation

Answer 6

• Boiling point is elevated when solute is dissolved in solution. Addition of solute to solvent decreases solvent vapor pressure and thus more energy (higher temperature) is required to raise vapor pressure to ambient pressure levels.
• ΔT(b) = i K(b) m, where ΔT(b) is increase in boiling point, i = Van’t Hoff Factor, K(b) is proportionality constant, and m is molality of solution (mol/kg).
• ΔT(b) is change in temperature, not new boiling point.

Question 7

Freezing Point Depression

Answer 7

• Solute presence interferes with lattice formation of solvent molecules, and the solution requires more energy to be removed from the solution (lower temperature is required) for solution to solidify.
• ΔT(f) = i K(f) m.

Question 8

Osmotic Pressure

Answer 8

• Sucking pressure generated by solution to pull water into solution.
• Π = iMRT, where M is molarity of solution and R is ideal gas constant.