Physical Properties of Solutions Chapter 12 with bits of Chapter 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or.
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Physical Properties of Solutions
Chapter 12
with bits of Chapter 4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Review:
What is a solution?homogenous mixture of 2 or more substances
What is a solute?
What is a solvent?
LIQUID SOLUTIONS
Miscibility
Limit on the amount of one liquid that can dissolve in another
Ethanol and water are miscible in all proportions
Oil and water are immiscible. They cannot mix in any proportions.
Three types of interactions in the solution process:• solvent-solvent interaction• solute-solute interaction• solvent-solute interaction
Hsoln = H1 + H2 + H3
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 solvents
CCl4 in C6H6
polar molecules are soluble in polar solvents C2H5OH in H2O
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
dispersion of particles of one substance throughout a dispersing medium of another substance.
Colloid versus Solution
• collodial particles are much larger than solute molecules
• collodial suspension is not as homogeneous as a solution
COLLOID
TYNDALL EFFECT
Scattering of light beam caused by the reflection from suspended particles
COLLOID – TYNDALL EFFECT
SUSPENSION – TYNDALL EFFECT
SOLUTION – TYNDALL EFFECT
saturated solution: contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature
unsaturated solution: contains less solute than the solvent has the capacity to dissolve at a specific temperature
supersaturated solution: contains more solute than is present in a saturated solution at a specific temperature
SOLUTION SATURATION
WHAT IS A SUPERSATURATED
SOLUTION? Observe the heat pack:
What is inside the container?
Click the disc on the inside:
What happens?
Why does this occur?
SUPERSATURATION
Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate.
Seed Crystal Video
FACTORS AFFECTING THE RATE OF DISSOLUTION
To increase the rate of dissolution:
Increase surface area of solute
Stirring or shaking to increase contact between the solvent and solute surface
Increase temperature, more collisions between solute and solvent
What would you do to
make lemonade mix faster?
CRYSTALLIZATION VS PRECIPITATION
Crystallization:process in which dissolved solute comes out of solution and forms crystals
Precipitation:when an insoluble solid forms from the reaction of two solutions
ELECTROLYTES
Electrolyte: substance that, when dissolved in water, results in a solution that can conduct electricity
• can be strong or weak
Nonelectrolyte: substance that, when dissolved, results in a solution that does not conduct electricity
ELECTROLYTES
____________ ____________ ____________
ELECTROLYTES DEMO
Water
Sodium Chloride Solution
Sugar Solution
Pure Acetic Acid
Acetic Acid Solution
Gatorade
Rubbing Alcohol
Strong Electrolyte – 100% dissociation
NaCl (s) Na+ (aq) + Cl- (aq)H2O
Weak Electrolyte – not completely dissociated
CH3COOH CH3COO- (aq) + H+ (aq)
Cations (+) and Anions (-)
WHAT CAUSES A STRONG
ELECTROLYTE?
Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C6H12O6 (s) C6H12O6 (aq)H2O
Strong Electrolyte Weak Electrolyte Nonelectrolyte
HCl CH3COOH (NH2)2CO
HNO3 HF CH3OH
HClO4 HNO2 C2H5OH
NaOH H2O C12H22O11
Ionic Compounds
WHAT CAUSES A NONELECTROLYTE?
Hydration: process in which an ion is surrounded by water
H2O
HOW DOES A SOLUTION FORM?
Remember the polarity of water:
How will the water molecule arrange around a specific ion?
HYDRATION ON THE PARTICLE LEVEL
the molecules are arranged in a specific manner
Solvation Process Simulation
PRECIPITATION REACTIONS
Precipitate: insoluble solid that separates from solution
molecular equation
ionic equation
net ionic equation
Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3
-
Na+ and NO3- are spectator ions
PbI2
Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)
precipitate
Pb2+ + 2I- PbI2 (s)
WRITING NET IONIC EQUATIONS
1. Write the balanced molecular equation.
2. Determine precipitate from solubility rules
3. Write the ionic equation showing the strong electrolytes
4. Cancel the spectator ions on both sides of the ionic equation
DON’T FORGET YOUR SOLUBILITY RULES!!!
NET IONIC EQUATION PRACTICE
AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)
Ag+ + NO3- + Na+ + Cl- AgCl (s) + Na+ + NO3
-
Ag+ + Cl- AgCl (s)
Write the net ionic equation for the reaction of silver nitrate with sodium chloride.
CONCENTRATION
Concentration: amount of solute present in a given quantity of solvent or solution
Percent by Mass
% by mass = x 100%mass of solutemass of solute + mass of solvent
= x 100%mass of solutemass of solution
Mole Fraction (X)
XA = moles of A
sum of moles of all components
CONCENTRATION CALCULATIONS
M =moles of solute
liters of solution
Molarity (M)
Molality (m)
m =moles of solute
kilograms of solvent
HOW TO CALCULATE CONCENTRATION
Why is molarity not a preferred unit under certain conditions?Volume of a solution
changes with temperature
CALCULATIONS
Molarity:
How many grams of NaOH are needed to make 250 mL of a 5.00 M NaOH solution?
Molality:
What is the molality of a solution of 10.0 g of NaOH dissolved in 0.100 kg of water?
m =moles of solute
mass of solvent (kg)
M =moles of solute
liters of solution
Total mass of solution = mass of solute + mass of solvent
IMPORTANT RELATIONSHIPS
WHAT IS THE MOLALITY OF A 5.86 M ETHANOL (C2H5OH) SOLUTION
WHOSE DENSITY IS 0.927 G/ML?1. Assume 1 L of solution
5.86 moles ethanol (solute)2. Find grams of solute
= 270 g eth3. Find grams of solution
(1000 mL x 0.927 g/mL) = 927 g solution4. Find kg of solvent
g of solvent = g of soln – g of solute = 657 g = .657 kg
5. Calculate molality= 8.92 m
WHAT IS THE MOLALITY OF A 62.5% SODIUM CHLORIDE
SOLUTION?1. Assume 100 grams of solution
2. Find moles of solute
3. Find kg of solvent
4. Calculate molality
ADDITIVE CONCENTRATION
If 25.0 mL of 3.75 M NaCl solution is added to 50.00 mL of 1.35 M NaCl solution. What is the molarity of the resulting solution?
SOLUTION STOICHIOMETRY
50.0 mL of a 2.0 M solution of AgNO3 is reacted with a 50.0 mL of a 1.5 M solution of Na3PO4. How many grams of Ag3PO4 are produced?
1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
GRAVIMETRIC ANALYSIS
GRAVIMETRIC ANALYSIS CONT.
3. Filter and dry precipitate
4. Weigh precipitate
5. Use chemical formula and mass of precipitate to determine information about unknown reactants
Dilution
Add Solvent
Moles of solutebefore dilution (i)
Moles of soluteafter dilution (f)=
MiVi MfVf=
DILUTIONprocedure for preparing a less concentrated solution from a more
concentrated solution
How would you prepare 60.0 mL of 0.2 MHNO3 from a stock solution of 4.00 M HNO3?
MiVi = MfVf
Mi = 4.00 Mf = 0.200 Vf = 0.06 L Vi = ? L
Vi =MfVf
Mi
=0.200 x 0.06
4.00= 0.003 L = 3 mL
3 mL of acid + 57 mL of water = 60 mL of solution
HOW TO PREPARE A SOLUTION
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature
TEMPERATURE AND SOLUBILITY
Gas solubility and temperature
solubility usually decreases with
increasing temperature
TEMPERATURE AND SOLUBILITY
HENRY’S LAW IS USED TO MEASURE VAPOR
PRESSURE Some gases react with water and cause a
greater solubility than expected
Exceptions to Henry’s Law
Carbon Dioxide
CO2 + H2O H2CO3
Ammonia
NH3 + H2O NH4+OH-
SOLUBILITY CURVES
Identify the solubility at a specific temperature.
Identify the temperature at which something can dissolve.
Identify whether something is saturated, unsaturated, or supersaturated.
Identify which one is a gas.
Identify solubility in different amounts of water.
Identify how much will crystallize with a temperature change.
COLLIGATIVE PROPERTIES OF
NONELECTROLYTES Colligative properties: properties that
depend only on the number of solute particles in solution and not on the nature of the solute particles
Vapor Pressure Lowering
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure
Calculating Partial Vapor Pressure for Solvent
Finding the change in partial pressure with one solute:
X2 = 1 – X1
P 10 = vapor pressure of pure solvent
X1 = mole fraction of the solvent
X2 = mole fraction of the solute
P1 = X1 P 10
VAPOR PRESSURE LOWERING
(Xsolute + Xsolvent = 1)
P = X2 P 10
Tb = Tb – T b0
T b = boiling point of the pure solvent0
T b = boiling point of the solution
Tb = Kb m
m = molality of the solution
Kb = molal boiling-point elevation constant (0C/m)
BOILING-POINT ELEVATION
Tf = T f – Tf0
T f = freezing point of the pure solvent0
T f = freezing point of the solution
Tf = Kf m
m = molality of the solution
Kf = molal freezing-point depression constant (0C/m)
FREEZING-POINT DEPRESSION
What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g.
Tf = Kf m
m =moles of solute
mass of solvent (kg)= 2.41 m=
3.202 kg solvent
478 g x 1 mol62.01 g
Kf water = 1.86 0C/m
Tf = Kf m = 1.86 0C/m x 2.41 m = 4.48 0C
Tf = T f – Tf0
Tf = T f – Tf0 = 0.00 0C – 4.48 0C = -4.48 0C
Osmosis: selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.
semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.
Osmotic pressure () : pressure required to stop osmosis
dilutemore
concentrated
OSMOTIC PRESSURE ()
HighP
LowP
= MRT
M = molarity of the solution
R = gas constant (0.0821 L·atm/mol·K)
T = temperature (in K)
OSMOTIC PRESSURE ()
OSMOTIC PRESSURE CALCULATION
The average osmotic pressure of seawater is about 30.0 atm at 25oC. Calculate the molar concentration of an aqueous solution of urea that is isotonic with seawater.
Solution:M = π = 30.0 atm
RT (0.0821 Latm/molK)(298 K)
= 1.23 M
Vapor-Pressure Lowering P1 = X1 P 10
Boiling-Point Elevation Tb = Kb m
Freezing-Point Depression Tf = Kf m
Osmotic Pressure () = MRT
EQUATION SUMMARY
0.1 m NaCl solution 0.1 m Na+ ions & 0.1 m Cl- ions
0.1 m NaCl solution 0.2 m ions in solution
van’t Hoff factor (i) = actual number of particles in soln after dissociation
number of formula units initially dissolved in soln
nonelectrolytesNaCl
CaCl2
i should be
12
3
COLLIGATIVE PROPERTIES OF
ELECTROLYTE SOLUTIONS
Boiling-Point Elevation Tb = i Kb m
Freezing-Point Depression Tf = i Kf m
Osmotic Pressure () = iMRT
ELECTROLYTE SOLUTION EQUATIONS
VAN’T HOFF FACTOR
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