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CH 11: Properties of Solutions
1. Describing Solutions – concentration units2. Energetics of solution formation3. Factors impacting solubility – P and T4. Colligative Properties of solutions
• BP elevation• FP depression• Osmotic pressure• Vapor Pressure
Terms
• Solution – homogeneous mixture• Solvent – generally the larger component of
the solution– Determines the physical state of the solution
• Solute – generally the smaller component of the solution– Solute is dispersed in the solvent
Solution Composition
• Concentrated solution – relatively large amount of solute
• Dilute solution – relatively small amount of solute
Solution Composition
• Unsaturated solution –solution with less than the maximum amount of solute that will normally dissolve at a given temperature
• Saturated solution - solution with maximum amount of solute that will normally dissolve at a given temperature
Solution Composition
• Super-saturated solution - solution with more than the maximum amount of solute that will normally dissolve at a given temperature
Concentration Units
Molarity (M) = moles solute/Liters solution
Molality (m) = moles solute/kg solvent
Mass % = Mass solute/mass solution x100%
Mole fraction () = moles A/total moles
Normality
Normality (N) = # gram equivalent wt./L solution– Gew = mass of an acid or base that produces 1
mole of H+ or OH -1
Normality = Molarity x (# H+ or OH -1 /mol)– 1 M HCl = 1 N HCl– 1 M H2SO4 = 2 N H2SO4
For acid base titrations:(NAcid) (VAcid) = (NBase) (VBase)
Starting with Molarity
Solution: – 3.75 M H2SO4 solution with a density of 1.23 g/mL
Calculate: – Mass % – Molality– mole fraction of H2SO4
Starting with Masses
Solution: – A solution is made by combining 66.0 grams of
acetone (C3H6 O) with 146.0 grams of water.– Solution has a density of 0.926 g/mL
Calculate: – Molarity – need volume of solution– Mass %– Molality– Mole fraction of acetone
Starting with Mass %
Solution: – 35.4 % H3PO4
– Density of 1.20 g/mL
Calculate: – Molarity – Molality– Mole fraction of H3PO4
Starting with Molality
Solution: – 2.50 m HCl solution– Density of 1.15 g/mL
Calculate: – Molarity – need _______ – Mass %– Mole fraction of HCl
Solution Formation
Formation of a solution involves 3 steps1. Separate the solute particles• expand the solute
2. Separate the solvent particles• Expand the solvent
3. Form the solution– Solute and solvent interact
Solution Formation
• Each step of solution formation involves energy and has a H.
H1 = energy needed to separate the solute
H2 = energy needed to separate the solvent
H3 = energy released when solution forms
Solution Formation
HsolutionH1 + H2 + H3
Solutions form when the Hsolution is a small value – see page 504
Factors Impacting Solubility
• Pressure– Pressure has little impact on the solubility of
liquids and solids– Pressure has a significant impact on the solubility
of gases in a liquid• The higher the pressure of gaseous solute above a
liquid the higher the concentration of the gas in the solution
Henry’s Law• Henry’s Law: C = kP
C = Concentration of dissolved gask = solution specific constantP = partial P of the solute gas above
the solution• What does Henry’s Law mean?– No calculations required.
Page 506
Temperature and Solubility
• Temperature has variable effects on the amount of solid that will dissolve in an aqueous solution!– See figure 11.6 page 508
• Solutes will dissolve more rapidly at higher temperatures
Temperature and Solubility
• The solubility of a gas in water decreases as temperature increases.– See figure 11.7 on page 508
– Thermal pollution – read the story on page 510 when you get a chance
Vapor Pressure of Solutions
• See Raoult’s Law on page 510
• Psolution = solventsolvent P0 solventsolvent
Colligative Properties
• Colligative properties– properties of a solution that depend upon the
amount of dissolved solute, not the identity of the solute.• Freezing point depression• Boiling point elevation• Osmotic Pressure
• Note: I will be weaving section 11.7 and the van’t Hoff factor (i) into my consideration of these properties and not consider it separately.
1. Calculating the bp or fp of a solution2. Calculating the molar mass of a solute from
fp or bp data