properties of solutions: ways of expressing concentrations weight percentage = mass of component in...
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Properties of Solutions: Ways of Expressing ConcentrationsProperties of Solutions: Ways of Expressing Concentrations
Weight percentage = mass of component in solution
total mass of solution
Parts per million (ppm) = mass of component in solution
total mass of solution
A 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 ppm
6.9g
106.9 gx 100 = 6.5%
x 100
x 106
5.4 x 10-6 2.5 g
x 106ppm =
Wt % of component =
= 2.2ppm
Mole fraction, Molarity , and MolalityMole fraction, Molarity , and MolalityMole fraction of a component = Moles component
Total moles of all components
Calculate the mole fraction of HCl in a solution of HCl containing 36% HCl by weight.
36 g HCl1 mole HCl36.5 g HCl
= 0.99 mol HCl
64 g H2O1 mole H2O
18 g H2O = 3.6 mol H2O
XHCl = Mole HCl
Moles HCl + H2O= 0.99 mol
4.6 mol= 0.22
Mole fraction, Molarity , and MolalityMole fraction, Molarity , and MolalityMolarity = Molarity = Moles of soluteMoles of solute
Liters of solutionLiters of solution
What 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 0.0100 mol ascorbic acid.
1.80 g C6H8O6
1 mol C6H8O6
176 g C6H8O6
= 0.0102 mol C6H8O6
Molarity = 0.0102 mol C6H8O6
.125 L soln= 0.0818 M
Mole fraction, Molarity , and MolalityMole fraction, Molarity , and Molality
Molality = moles of soluteMolality = moles of solute
Kg of solventKg of solvent
What is the molality of a solution made by dissolving 5.0 g of toluene (C7H8) in 25 g of benzene (C6H6)?
5.0 g C7H8 1 mol C7H8
92 g C7H8
= 0.054 mol C7H8
Molality = 0.054 mol C7H8
.025 kg C6H6
= 2.2 m
Properties of Solutions: The Solution ProcessProperties of Solutions: The Solution Process
Na+Cl-
-
-+
+
+
+
-
-
Cl-
Na+
Solvation or hydration
Na+
Na+
Na+
Cl-
Cl-
Cl-
Cl-
Na+
Cl-
Properties of Solutions: The Solution ProcessProperties of Solutions: The Solution ProcessEnergy Changes and Solution FormationEnergy Changes and Solution Formation
Hsoln = H1 + H2
+ H3
Solute-solute interactions
Solvent-solvent interactions
Solute-solvent interactions
Properties of Solutions: The Solution ProcessProperties of Solutions: The Solution ProcessEnergy Changes and Solution FormationEnergy Changes and Solution Formation
The overall change in enthalpy can be exo- or endothermic
NaOH: Hsoln = -44.48 NH4OH: Hsoln
= 26.4
This explains why “like dissolves like”
Properties of Solutions: Solution Formation, SpontaneityProperties of Solutions: Solution Formation, Spontaneityand Disorder…and Disorder…WHY DOES THIS STUFF DISSOLVEWHY DOES THIS STUFF DISSOLVE??
bp = 77 bp = 69
London dispersion forces
Little energy is exchanged
Properties of Solutions: Solution Formation, SpontaneityProperties of Solutions: Solution Formation, Spontaneityand Disorder…and Disorder…WHY DOES THIS STUFF DISSOLVEWHY 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 spontaneously
When molecules of different types are brought together, an increase in disorder occurs spontaneously unless the molecules are restrained sufficiently by strong intermolecular forces. Salt does not dissolve in gasoline because strong forces are holding the Na+ andCl- ions together and the intermolecular forces associated with nonpolar substances is not sufficient to dislodge them.
Properties of Solutions: Saturated Solutions and SolubilitycProperties of Solutions: Saturated Solutions and SolubilitycAs 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.
Solute + Solvent Solutiondissolve
crystallize
Saturated: a solution with undissolvedsolute
Supersaturated: a solution which contains a greater amount of solute than needed toform a saturated solution
Properties of Solutions: Factors Affecting SolubilityProperties of Solutions: Factors Affecting Solubility
•As a rule, solubility increases with increasing molecular mass
•Polar liquids tend to dissolve in polar solvents. If the dissolve they are miscible.If they do not dissolve they are immiscible
Properties of Solutions: Factors Affecting SolubilityProperties of Solutions: Factors Affecting SolubilityHydrogen-boning interactions between solute and solvent may lead to high solubility
Ethanol and ethanol Ethanol and water
Because of H-bonding, solute-solute, solvent-solvent, and solute-solventinteractions are not appreciably different.
There is no significant change in the environment
However, the numbers carbon atoms in an alcohol does effect it solubility in water.
Properties of Solutions: Factors Affecting SolubilityProperties of Solutions: Factors Affecting Solubility
As the length of the chain increases, the OH groups decrease leading to a decrease in solubility
Glocuse has 5-OH groups on a six carbon framework which makes themolecule fairly soluble in water
Properties of Solutions: Factors Affecting SolubilityProperties of Solutions: Factors Affecting SolubilitySubstances with similar intermolecular attractive forces tend to be solublein one another….LIKE DISSOLVES LIKE
Properties of Solutions: Factors Affecting SolubilityProperties of Solutions: Factors Affecting SolubilitySubstances with similar intermolecular attractive forces tend to be solublein one another….LIKE DISSOLVES LIKE
Predict whether each of the following substances is more likely to dissolve in carbontetrachloride or water: C7H16. NaHCO3, HCl
Pressure EffectsPressure 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.
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 = kPg
Cg = (6.8 x 10-4 mol/l-atm)(1.56 atm) Cg = 0.0011
Temperature EffectsTemperature Effects
In general, the solubility of gases decreases as temperature increases
Temperature EffectsTemperature Effects
In general, the solubility of of ionic compounds, solids, normally increases as the temperature increases.
Colligative PropertiesColligative PropertiesThe increase or decrease of of the concentrations and not the kinds of particles in solutions can effect certain physical properties of solutions
•Freezing point depression of a solution•Boiling point elevation of a solution•vapor pressure; Raoult’s Law•Osmotic pressure
Colligative means “depending upon the collection”; colligative properties depend upon the collective effect of the
number of solute particles
Colligative PropertiesColligative Properties
Lowering the Vapor Pressure: TRY EXPLAINING THIS ONE!!
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 phase
The extent to which a nonvolatile solute lowers the vapor pressureis proportional to the concentration
Raoult’s Law: Calculating the vapor Raoult’s Law: Calculating the vapor pressure of a solution based upon the pressure of a solution based upon the amount of solute being added to the amount of solute being added to the
solution.solution.
PA = XAPA° Where PA is the vapor pressure of the solution, XA is the
mole fraction of solventsolvent, and P°A is the vapor pressure of the pure
solvent
Colligative Properties are the first evidence that salts break up into ions.
Xa = Mole of solvent
Moles of solvent + moles of solute x ii
If 10g of MgClIf 10g of MgCl2 2 is added to 100ml of is added to 100ml of
HH22O at 23O at 23ºC, ºC, what would be the vapor what would be the vapor
pressure. The vapor pressure for water pressure. The vapor pressure for water at this temperature is 21.07 torr.at this temperature is 21.07 torr.
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 torr
P A = XA P°A + P B = XB P°B
Properties of Solutions:Boiling Point Properties of Solutions:Boiling Point Elevation and Freezing Point DepressionElevation 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 constant
For 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 of
0.52°C higher than pure water.
Boiling Point ElevationBoiling Point Elevationand Freezing Point Depressionand Freezing Point Depression
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 solvent
If 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 constant
For 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 of 1.86 °C lower than pure water.
Calculate the freezing point and the boiling point of a solution of 100 g of ethylene glycol (C2H6O2), antifreeze in
900 g of H2O.
m = Moles C2H6O2
Kilograms H2O
100 g C2H6O2
.900 kg H2O1 mol C2H6O2
62.0 g C2H6O2
= 1.79 m
Tf = Kf m = 1.86 °C m
(1.79 m ) = 3.33 °C
Therefore freezing point = -3.33 °C
=
Tb = Kbm = .52 °C m
(1.79 m ) = 100.93 °C
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 3.63
0.49 = 3.63 (.64g mole )
xg
.036kg
Properties of Solutions:OsmosisProperties of Solutions:Osmosis
The net movement of solvent is always toward the more concentratedsolution
The pressure required to prevent osmosis is called theosmotic pressure, , of the solution, where = MRT
Hypertonic Solution Hypotonic Solution
Properties of Solutions:OsmosisProperties of Solutions:Osmosis
Properties of Solutions:OsmosisProperties of Solutions:OsmosisSample problem: The average osmotic pressure of blood is 7.7 atm. At 25°C. What concentration of glucose (C6H12O6) would be isotonic with blood?
Lysozyme is an enzyme that breaks bacterial cell walls. a solution containing 0.150 g of this enzyme in 210 mL of solution has an osmotic pressure of 0.953 torr at 25ºC. What is the molar mass of Lysozyme?
π = MRT
.953 = .150g mole 62.3 298
xg
.21L
Properties of Solutions:ColloidsProperties of Solutions:Colloids
Suspensions that are the dividing Line Between Solutions and Heterogeneous Mixtures
Tyndell effect: a scattering of light by colloidal particles
Properties of Solutions:ColloidsProperties of Solutions:Colloids
Hydrophilic and Hydrophobic Colloids
The most important colloids are those in which the dispersing medium is waterThe most important colloids are those in which the dispersing medium is water
Hydrophilic colloids are kept in suspension by interactionwith surrounding water molecules
Properties of Solutions:ColloidsProperties of Solutions:Colloids
Hydrophilic and Hydrophobic Colloids
The most important colloids are those in which the dispersing medium is waterThe most important colloids are those in which the dispersing medium is water
Hydrophobic colloids can be stabilized in water by the adsorption of ions ontotheir surface
Properties of Solutions:ColloidsProperties of Solutions:Colloids
Hydrophilic and Hydrophobic Colloids
The most important colloids are those in which the dispersing medium is waterThe most important colloids are those in which the dispersing medium is water
Pa = Xa Paº
Xa= moles of solvent
moles of solvent + moles of solute x i
ΔTb = Kbm i
ΔTf = Kfm i
π = MRTi