SOLUTIONS
A. Solution formation and solubility
1. Factors that influence the rate of dissolving (how fast it dissolves)
a. Stirring (agitation) -- Increase rate of shaking, increase rate of dissolving
b. Temperature -- increase temperature, increase rate of dissolving
c. Particle size (surface area) -- decrease particle size, increase surface area, increae rate of dissolving
2. Saturated Solution -- contains maximum amount of solute for a given amount of solvent at a constant temperature
a. Crystals are solvated and solvated ions are desolvated at same rate -- dynamic equilibrium
3. Solubility -- amount of solute dissolved in a given quantity of solvent at a given temperature to make a saturated solution
4. Unsaturated -- a solution that contains less solute than a saturated solution (less than the max)
5. Miscible -- two liquids that dissolve in each other
6. Immiscible -- two liquids that do not dissolve in each other
B. Factors Affecting Solubility
1. Affect of Temperature
a. solid solute --> solubility generally increases as temperature increases
b. Gas solutes --> solubility generally decreases as temperature increases
2. Affect of Pressure
a. Gas solute --> solubility increases as pressure increases
b. Henry's Law -- solubility is directly proportional to pressure
1. S1/P1 = S2/P2
3. Supersaturated Solution -- a solution contains more solute than it should theoretically at a given temperature
a. Make by heating solution, adding more solute, and cooling back to original temperature
II. Concentrations of Solutions
A. Molarity (M) -- number of moles of solute dissolved per liter solution
1. Concentration -- a measure of amount of solute dissolved in a given amount of solvent
2. Dilute Solution -- contains low concentration of solute
3. concentrated solution -- contains high concentration of solute
a. Both are qualitative terms relative to each other
4. Quantitatively expressed as Molarity or "Molar"
a. M = (moles of solute)/(liters of solution)
B. Making Dilutions and Percent Solutions
1. Make solutions less concentrated by diluting it with a solvent
a. since only solvent changes, the number of moles stays the same
b. Moles solute before dilution = moles solute after dilution
c. Moles of solute = M x V (liters of solution)
1. Moles = M1V1 = M2V2
2. Percent of liquid solute in liquid solvent
a. % (v/v) = (volume of solute)/(volume of solution) x 100 %
3. Percent of solid solute in liquid solvent
a. % (m/v) = (mass solute)/(volume solution) x 100 %
III. Colligative Properties of solutions
A. Vapor Pressure
1. Colligative Properties -- properties that only depend on the number of particles dissolved in a given mass of solvent
2. Vapor Pressure is lowered by adding a solute
3. Reason: The solute particles occupy solvent molecules when solvated, therefore they can not escape
B. Boiling Point
1. boiling Point is raised by adding a solute
2. Reason: vapor pressure must equal atmospheric pressure, since vapor pressure is lowered, more energy is needed to boil, temperature rises
C. Freezing Point
1. Freezing Point is lowered by adding a solute
2. Reason: solute particles interfere with the formation of solid
D. All three colligative properties are proportional to the number of solute particles
1. Boiling point elevation -- difference in temperature between solution and pure solvent
2. freezing point depression -- difference in temperature between solution and pure solvent
IV. Calculations involving colligative Properties
A. Molality (m) -- the number of moles of solute dissolved per kilogram of solvent
1. m = (moles of solute)/(kilograms of solvent) = (moles of solute)/(1000 g of solvent)
B. Mole Fraction -- ratio of moles of solute in solution to the total muber of moles of solvent and solute
1. Xa = na/(na +nb) and Xb = nb/(na + nb)
a. Xa = mole fraction of solute, Xb = mole fraction of solvent, na = moles of solute, nb = moles of solvent
C. Boiling Point Elevation --- DeltaTb = Kb x m
1. Delta Tb = change in boiling point temperature, Kb = molal boiling point elevation constant
a. Units of Kb are in degrees C/m
2. Molecular solutes --> use equation as is written
3. Ionic solutes --> multiply number of ions by molality for m
4. Water: Kb = 0.512 C/m
D. freezing Point Depression -- Delta Tf = Kf x m
1. Delta Tf = change in freezing point temperature, Kf = molal freezing point depression constant
a. Units of Kf are in degress C/m
2. Water: Kf = 1.86 C/m
Outline based upon:
Matta, M. S., Staley, D. D., Waterman, E. L., & Wilbraham, A. C. (2000). Chemistry, Addison-Wesley. (5th ed.). Menlo Park, CA: Prentice Hall, pp. 501-527.
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