Presentation on theme: "Solutions & Colligative Properties"— Presentation transcript:
1Solutions & Colligative Properties AP Chemistry NotesSolutions & Colligative Properties
2Solutions…A solution is a homogenous mixture of two or more substances.The solute is(are) the substance(s) present in the smaller amount(s).The solvent is the substance present in the larger amount.
3Solutions…An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.nonelectrolyteweak electrolytestrong electrolyte
4Solutions…A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
5Solutions… DHsoln = DH1 + DH2 + DH3 Three types of interactions in the solution process:solvent-solvent; solute-solute; and solvent-soluteDHsoln = DH1 + DH2 + DH3
6Solutions…Two substances with similar intermolecular forces are likely to be soluble in each other.‘LIKE DISSOLVES LIKE’Non-polar molecules are soluble in non-polar solventsCCl4 in C6H6Polar molecules are soluble in polar solventsC2H5OH in H2OIonic compounds are more soluble in polar solventsNaCl in H2O or NH3 (l)
7Concentration…The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.Percent by Mass:=x 100%mass of solutemass of solution
8Concentration… Mole Fraction (X) moles of A XA = sum of moles of all components
9Concentration… Molarity: Molality: moles of solute M = liters of solutionm =moles of solutemass of solvent (kg)
10Concentration…What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is g/mL?m =moles of solutemass of solvent (kg)M =moles of soluteliters of solutionAssume 1 L of solution: 5.86 moles ethanol = 270 g ethanol927 g of solution (1000 mL x g/mL)mass of solvent = mass of solution – mass of solute= 927 g – 270 g = 657 g = kgm =moles of solutemass of solvent (kg)=5.86 moles C2H5OH0.657 kg solvent= 8.92 m
13Solubility… Pressure and Solubility of Gases The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).Mathematically expressed: c = kPc is the concentration (M) of the dissolved gasP is the pressure of the gas over the solutionk is a constant (mol/L•atm) that depends only on temperature
14Henry’s Law:The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).high Plow Phigh clow c
16Colligative Properties… Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.Vapor-Pressure LoweringBoiling Point ElevationFreezing Point DepressionOsmosis
17Vapor Pressure Lowering… Raoult’s law:P1 = X1 P 1P 1= vapor pressure of pure solventX1 = mole fraction of the solventIf the solution contains only one solute:X1 = 1 – X2P 1- P1 = DP = X2X2 = mole fraction of the solute
18Vapor Pressure Lowering… At a given temperature water has a vapor pressure of mmHg. Calculate the vapor pressure above a solution of g of sucrose (C12H22O11) in mL of water, assuming the water to have a density of g/mL.
20Vapor Pressure Lowering… 23.00 g of an unknown substance was added to g of water. The vapor pressure above the solution was found to be mmHg. Given that the vapor pressure of pure water at this temperature is mmHg, calculate the Molar Mass of the unknown.
22Vapor Pressure Lowering… PA = XA P AIdeal SolutionPB = XB P BPT = PA + PBPT = XA P A+ XB P B
23Vapor Pressure Lowering… At 20.0 oC the vapor pressures of methanol (CH3OH)and ethanol (C2H5OH) are 95.0 and 45.0 mmHg respectively. An ideal solution contains 16.1 g of methanol and 92.1 g of ethanol. Calculate the vapor pressure.
25Boiling Point Elevation… DTb = Tb – T bT b is the boiling point ofthe solutionT b is the boiling point ofthe pure solventTb > T bDTb > 0DTb = Kb mm is the molality of the solutionKb is the molal boiling-pointelevation constant (0C/m)
26Freezing Point Depression… DTf = T f – TfT f is the freezing point ofthe solutionT f is the freezing point ofthe pure solventT f > TfDTf > 0DTf = Kf mm is the molality of the solutionKf is the molal freezing-pointdepression constant (0C/m)
28DTf = Kf m Kf water = 1.86 0C/m DTf = Kf m What is the freezing point of a solution containing 478g of ethylene glycol (antifreeze) in 3202 g of water? GIVEN: The molar mass of ethylene glycol is g.DTf = Kf mKf water = C/m=3.202 kg solvent478 g x1 mol62.01 gm =moles of solutemass of solvent (kg)= 2.41 mDTf = Kf m= C/m x 2.41 m = CDTf = T f – TfTf = T f – DTf= C – C = C
29Summary…Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.Vapor-Pressure LoweringP1 = X1 P 1Boiling-Point ElevationDTb = Kb mFreezing-Point DepressionDTf = Kf mOsmotic Pressure (p)p = MRT
31Colligative Properties… Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.0.1 m NaCl solution m Na+ ions & 0.1 m Cl- ions0.1 m NaCl solution 0.2 m ions in solutionvan’t Hoff factor (i) =actual number of particles in soln after dissociationnumber of formula units initially dissolved in solni should be123NonelectrolytesNaClCaCl2
32Colligative Properties… Boiling-Point ElevationDTb = i Kb mFreezing-Point DepressionDTf = i Kf mOsmotic Pressure (p)p = iMRT
33Colligative Properties… At what temperature will a 5.4 molal solution of NaCl freeze?Solution:∆TFP = Kf • m • i∆TFP = (1.86 oC/molal) • 5.4 m • 2∆TFP = oCFP = 0 – 20.1 = oC
34Colligative Properties… Osmotic Pressure (p):Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.Osmotic pressure (p) is the pressure required to stop osmosis.moreconcentrateddilute
35Colligative Properties… HighPLowPp = MRTM is the molarity of the solutionR is the gas constantT is the temperature (in K)
36Colloids…A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.Colloid versus solution:Collodial particles are much larger than solute moleculesCollodial suspension is not as homogeneous as a solution