Presentation on theme: "Properties of Solutions: Ways of Expressing Concentrations"— Presentation transcript:
1 Properties of Solutions: Ways of Expressing Concentrations Weight percentage= mass of component in solutionx 100total mass of solutionParts per million (ppm)= mass of component in solutionx 106total mass of solutionA solution is made containing 6.9 g NaHCO3 per 100 g water. What is the weight percentage of solute in the solution? A 2.5 g sample of ground water was found to contain 5.4 micrograms of Zn2+. What is the concentration of Zn2+ in ppm6.9gWt % of component =x 100 = 6.5%106.9 g5.4 x 10-6ppm =x 106= 2.2ppm2.5 g
2 Mole fraction, Molarity , and Molality Mole fraction of a component =Moles componentTotal moles of all componentsCalculate the mole fraction of HCl in a solution of HCl containing 36% HCl by weight.1 mole HCl36 g HCl= 0.99 mol HCl36.5 g HCl1 mole H2O= 3.6 mol H2O64 g H2O18 g H2OMole HCl0.99 molXHCl === 0.224.6 molMoles HCl + H2O
3 Mole fraction, Molarity , and Molality Moles of soluteMolarity =Liters of solutionWhat is the molarity of an ascorbic acid solution (C6H8O6) prepared by dissolving1.80 grams in enough water to make 125 mL of solution. How many milliliters of thissolution contain mol ascorbic acid.1 mol C6H8O6= mol C6H8O61.80 g C6H8O6176 g C6H8O6mol C6H8O6Molarity == M.125 L soln
4 Mole fraction, Molarity , and Molality Molality = moles of soluteKg of solventWhat is the molality of a solution made by dissolving 5.0 g of toluene (C7H8) in 25 g of benzene (C6H6)?1 mol C7H85.0 g C7H8= mol C7H892 g C7H80.054 mol C7H8Molality == 2.2 m.025 kg C6H6
5 Solvation or hydration Properties of Solutions: The Solution ProcessSolvation or hydrationCl-Na+Na+-Na++Cl--Cl--Na++Na++Cl--Na++Cl-Cl-Cl-
6 Properties of Solutions: The Solution Process Energy Changes and Solution FormationSolute-solute interactionsSolvent-solvent interactionsSolute-solvent interactions Hsoln = H1 + H2 + H3
7 Properties of Solutions: The Solution Process Energy Changes and Solution FormationNaOH: Hsoln =NH4OH: Hsoln = 26.4The overall change in enthalpy can be exo- or endothermicThis explains why “like dissolves like”
8 Properties of Solutions: Solution Formation, Spontaneity and Disorder…WHY DOES THIS STUFF DISSOLVE?London dispersion forcesbp = 77bp = 69Little energy is exchanged
9 Properties of Solutions: Solution Formation, Spontaneity and Disorder…WHY DOES THIS STUFF DISSOLVE?Processes in which the energy content of the system decreases tend to occurspontaneously.Processes in which the disorder of the system increases tend to occur spontaneouslyWhen molecules of different types are brought together, an increase in disorder occursspontaneously unless the molecules are restrained sufficiently by strong intermolecularforces. Salt does not dissolve in gasoline because strong forces are holding the Na+ andCl- ions together and the intermolecular forces associated with nonpolar substances isnot sufficient to dislodge them.
10 Properties of Solutions: Saturated Solutions and Solubilityc As solid solute begins to dissolve in a solvent, the concentrations of solute particlesin solution increases, so the chances of their colliding with the surface of the solidincreases. This may lead to crystallization.Saturated: a solution with undissolvedsolutedissolveSolute + Solvent SolutioncrystallizeSupersaturated: a solution which containsa greater amount of solute than needed toform a saturated solution
11 Properties of Solutions: Factors Affecting Solubility As a rule, solubility increases with increasing molecular massPolar liquids tend to dissolve in polar solvents. If the dissolve they are miscible.If they do not dissolve they are immiscible
12 Properties of Solutions: Factors Affecting Solubility Hydrogen-boning interactions between solute and solvent may lead to high solubilityBecause of H-bonding, solute-solute, solvent-solvent, and solute-solventinteractions are not appreciably different.Ethanol and ethanolEthanol and waterThere is no significant change in the environment
13 Properties of Solutions: Factors Affecting Solubility However, the numbers carbon atoms in an alcohol does effect it solubility in water.As the length of the chain increases, the OH groups decrease leading to a decrease insolubility
14 Properties of Solutions: Factors Affecting Solubility Substances with similar intermolecular attractive forces tend to be solublein one another….LIKE DISSOLVES LIKEGlocuse has 5-OH groups on a six carbon framework which makes themolecule fairly soluble in water
15 Properties of Solutions: Factors Affecting Solubility Substances with similar intermolecular attractive forces tend to be solublein one another….LIKE DISSOLVES LIKEPredict whether each of the following substances is more likely to dissolve in carbontetrachloride or water: C7H16. NaHCO3, HCl
16 Pressure EffectsThe solubility of a gas in any solvent is increased as the pressure of the gas over the solvent increasesBy contrast the solubility of solids and liquids are not appreciable affected by pressure.
17 The relationship between pressure and solubility is expressed by Henry’s Law: Cg = kPg where Cg is the solubility of the gas in the solution phase, Pg is the partial pressure of the gas over the solution, and k is a Henry’s law constant which differs from one solute-solvent pair to another.For example the solubility of N2 gas in water at 25 ° C and 0.78 atm. is 5.3 x 10-4 Mk = 5.3 x 10-4 M/0.78 = 6.8 x 10-4 mol/l-atm. Assume that the partial pressure of the N2 is doubled, Henry’s law, Cg = kPg predicts that the solubility will also double.Cg = kPgCg = (6.8 x 10-4 mol/l-atm)(1.56 atm)Cg =
18 In general, the solubility of gases decreases as temperature increases Temperature EffectsIn general, the solubility of gases decreases as temperature increases
19 Temperature EffectsIn general, the solubility of of ionic compounds, solids, normally increases as the temperature increases.
20 Colligative Properties The increase or decrease of of the concentrations and not the kinds of particles in solutions can effect certain physical properties of solutionsFreezing point depression of a solutionBoiling point elevation of a solutionvapor pressure; Raoult’s LawOsmotic pressureColligative means “depending upon the collection”; colligative properties depend upon the collective effect of the number of solute particles
21 Lowering the Vapor Pressure: TRY EXPLAINING THIS ONE!! Colligative PropertiesLowering the Vapor Pressure: TRY EXPLAINING THIS ONE!!
22 Lowering the Vapor Pressure: Explaining How it is Done!! A non-volatile solute added to a solvent reduces the capacity of thesolvent molecules in the liquid phase to move into the gas phaseThe extent to which a nonvolatile solute lowers the vapor pressureis proportional to the concentration
23 Raoult’s Law: Calculating the vapor pressure of a solution based upon the amount of solute being added to the solution.PA = XAPA° Where PA is the vapor pressure of the solution, XA is the mole fraction of solvent, and P°A is the vapor pressure of the pure solvent
24 Colligative Properties are the first evidence that salts break up into ions. Xa = Mole of solventMoles of solvent + moles of solute x iIf 10g of MgCl2 is added to 100ml of H2O at 23ºC, what would be the vapor pressure. The vapor pressure for water at this temperature is torr.
25 What is the vapor pressure of a solution made with 1 mol of Benzene and 2 mol of toluene at 20ºC and the mole fraction of the vapor? Benzene = 75 torr and Toluene = 22 torrP A = XA P°A + P B = XB P°B
26 Properties of Solutions:Boiling Point Elevation and Freezing Point Depression
27 Boiling Point Elevation and Freezing Point Depression Because nonvolatile solutes lower the vapor pressure of a solution, a higher temperature is required to cause the solution to boil.Because the vapor pressure of the solution is lower than that of the solvent at all temps, in accordance to Raoult’s Law, the higher temperature is required to attain a vapor pressure of 1 atm. Tb = Kb m , where Tb is directly proportional to the number of solute particles per moles of solvent molecules, and Kb is called the molal boiling-point-elevation constantFor example, the Kb of water is 0.52 °C/m; therefore a 1m solution of sucrose or any other aqueous solution that is 1m in nonvolatile solute particles will boil at a temperature of0.52°C higher than pure water.
28 The freezing point corresponds to the temperature at which the vapor pressures of the solid and liquid phases are the same. The freezing point of a solution is lowered because the solute is not normally soluble in the solid phase of the solventIf the solute is nonvolatile, the vapor pressure of the solution is reduced in proportion to the mole fraction of solute. Tf = Kf m , where Tf is directly proportional to the number of solute particles per moles of solvent molecules, and Kf is called the molal-freezing-point-depression constantFor example, the Kf of water is 1.86 °C/m; therefore a 0.5 m solution of NaCl or any other aqueous solution that is 1m in nonvolatile solute particles will freeze at a temperature of1.86 °C lower than pure water.
29 = 1.79 m = Therefore freezing point = -3.33 °C = 100.93 °C m Calculate the freezing point and the boiling point of a solution of 100 g of ethylene glycol (C2H6O2), antifreeze in 900 g of H2O.Moles C2H6O2100 g C2H6O21 mol C2H6O2m ==.900 kg H2OKilograms H2O62.0 g C2H6O2= 1.79 m Tf = Kf m= °C(1.79 m )= 3.33 °CmTherefore freezing point = °C Tb = Kbm= °C(1.79 m )= °Cm
30 ΔTb = Kbm KB for adrenaline is 3.63 0.49 = 3.63 (.64g mole ) .036kg Adrenaline is the hormone that triggers the release of extra glucose molecules in times of stress or emergency. A solution of 0.64 g of adrenaline in 36.0 g of CCl4 elevates the boiling pt. by 0.49ºC. What is the molar mass?ΔTb = Kbm KB for adrenaline is 3.630.49 = 3.63 (.64g mole )xg.036kg
31 Properties of Solutions:Osmosis The pressure required to prevent osmosis is called theosmotic pressure, , of the solution, where = MRTThe net movement of solvent is always toward the more concentratedsolution
32 Properties of Solutions:Osmosis Hypertonic SolutionHypotonic Solution
33 Properties of Solutions:Osmosis Sample problem: The average osmotic pressure of blood is 7.7 atm. At 25°C. What concentration of glucose (C6H12O6) would be isotonic with blood?
34 Lysozyme is an enzyme that breaks bacterial cell walls Lysozyme is an enzyme that breaks bacterial cell walls. a solution containing g of this enzyme in 210 mL of solution has an osmotic pressure of torr at 25ºC. What is the molar mass of Lysozyme?π = MRT.953 = .150g molexg.21L
35 Properties of Solutions:Colloids Suspensions that are the dividing Line Between Solutions and Heterogeneous MixturesTyndell effect: a scattering of light by colloidal particles
36 Properties of Solutions:Colloids The most important colloids are those in which the dispersing medium is waterHydrophilic and Hydrophobic ColloidsHydrophilic colloids are kept insuspension by interactionwith surrounding watermolecules
37 Properties of Solutions:Colloids The most important colloids are those in which the dispersing medium is waterHydrophilic and Hydrophobic ColloidsHydrophobic colloids can be stabilized in water by the adsorption of ions ontotheir surface
38 Properties of Solutions:Colloids The most important colloids are those in which the dispersing medium is waterHydrophilic and Hydrophobic Colloids
39 Xa= moles of solvent moles of solvent + moles of solute x i Pa = Xa PaºXa= moles of solventmoles of solvent + moles of solute x iΔTb = Kbm iΔTf = Kfm iπ = MRTi