Transcript Chapter 12. Solutions

Chemistry 102(01) Spring 2002
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Instructor: Dr. Upali Siriwardane
e-mail:[email protected]
Office: CTH 311 Phone 257-4941
Office Hours:
8:00-9:00 & 11:00-12:00 a.m., M, W,
8:00-10:00 a.m., Tu,Th, F
March 27,
April 26,
May 15,
May 16,
2002 (Test 1): Chapter 12 &13.
2002(Test 2): Chapter 14 & 15.
2002 (Test 3): Chapter 15 & 17.
2002 (Comprehensive Test): Chapters 12,13,14,15,17
Chapter 12. Physical
Properties of Solutions
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solutions
Solubility gases :Henry's Law.
Concentration units.
Energy changes that occur in the solution
process
Solubilities of substances in various solvents
Colligative properties.
Colligative properties of electrolyte solutions.
Colloid, true solution and suspension.
Solutions
 Homogeneous
Mixtures
 Types of solutions
• Mixture of Gases
• Liquid solutions (L+S,L+L,L+G)
• Solid solutions (S+S,alloys)
• Aerosols (L+G)
• Foam (S+G)
Solution Components
 Solute
–smaller amount
 Solvent
–larger amount
“Like
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dissolves like.”
Materials with similar polarity are soluble
in each other. Dissimilar ones are not.
Miscible
Liquids that are soluble in each other in
all proportions such as ethanol and water.
Immiscible
Liquids that are not soluble in each other
such as hexane and water.
Solubility of Salts
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SOLUBILITY RULES
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SOME SALTS ARE SOLUBLE
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SOME ARE INSOLUBLE
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THERE ARE DEGREES OF SOLUBILITY
Amount of Solute
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solution that contains as much it
can hold is called Saturated
solution
 A solution that contains less than
maximum amount is called
unsaturated solution
 A solution that contains more than
maximum amount is called
supersaturated solution
Factors Affecting Solubility
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Miscibility of solute and solvent-
”Like dissolves like”
Heat of solution, DH(solution)
exothermic -cooling helps
endothermic-heating helps
 Gases:cooling & pressure helps
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Identify Polar and Non-polar groups in
Covalent Molecules
Acetic acid
HC2H3O2
CH3COOH
Hexanol
C6H13OH
Hexane
C6H14
Like Dissolves Like
Propanoic acid
C2H5COOH
Solution Process of Ionic Compounds
Temperature and solubility
Solubility
(g/100ml water)
300
SO2
KCl
glycine
NaBr
KNO3
sucrose
200
100
0
0
20
40
60
80
Temperature (oC)
100
Pressure and solubility of gases
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Increasing the pressure of a gas above a
liquid increases the concentration of the
gas.
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This shifts the equilibrium, driving
more gas into the liquid.
Henry's law
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At constant temperature, the solubility of
a gas is directly proportional to the
pressure of the gas above the solution.
S = kH p
p= partial pressure of gas above the
solution in atm.
S= concentration of gas in the solution
in mol/L.
kH= Henry's constant which is
characteristic of the gas and the
solvent.
Electrolytes
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Solutes which dissolves in water to form
conducting solution- Electrolytes
Solutes which dissolves in water to from
non-conducting solution-Non-
Electrolytes
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Solutes which dissolves in water to from
weakly conducting solution -Weak-
Electrolytes
Concentration Units
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a) Molarity (M)
b) Normality (N)
c) Molality (m)
d) Mole fraction (Ca)
e) Mass percent (% weight)
f) Volume percent (% volume)
g) "Proof"
h) ppm and ppb
Molarity(M)
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moles of solute
Molarity (M) = -----------------------Liters of solution
Calculate the normality of the
solution, which is prepared by
dissolving 25 g of H2SO4 in
water to a final volume of 2L.
M.W. (H2SO4) = 98.08 g/mole
Molality (m)
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moles of solute
Molality (m) = -----------------------kg of solvent
Calculate the molality of
C2H5OH in water solution which
is prepared by mixing 75.0 mL of
C2H5OH and 125 g of H2O at
o
20 C. The density of C2H5OH is
0.789 g/mL.
Mole fraction (Ca)
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Ca
moles of solute (substance)
= ------------------------------------moles of solute + solvent
Calculate the mole fraction of
benzene in a benzene(C6H6)chloroform(CHCl3) solution
which contains 60 g of benzene
and 30 g of chloroform.
M.W. = 78.12 (C6H6)
M.W. = 119.37 (CHCl3)
When 100. mL of 0.125 M HCl is
diluted to 250. mL, the resulting
MOLARITY of the HCl solution
is:
a) 0.625 M
b) 0.250 M
c) 0.0500 M
d) 0.0250 M
e) none of these
Mass (w/w) % or Weight %
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Mass of solute
Mass (w/w) % = ---------------------- x 100
Mass of solution
What is the mole fraction of
ethanol, C2H5OH, in a methanol
solution that is 40.%(w/w)
ethanol, C2H5OH, by mass?
a. 0.40 b. 0.46 c. 0.21 d. 0.54
Calculate the molarity of a
solution of water/alcohol
containing 35% C2H5OH by
weight. The density of this
solution is 1.10 g/mL.
Volume (v/v) % or Volume %
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Volume of solute
Volume (v/v) % =----------------------x 100
Volume of solution
Proof = Volume % x 2
A solution of hydrogen peroxide
is 30.0% H2O2 by mass and has a
density of 1.11 g/cm3. The
MOLARITY of the solution is:
a) 7.94 M b) 8.82 M c) 9.79 M
d) 0.980 e) none of these
M.W. = 34.02 (H2O2)
ppm & ppb (w/w or v/v)
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Mass (volume) of solute
ppm = -------------------------------- x 106
Mass (volume) of solution
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Mass (volume) of solute
ppb = -------------------------------- x 109
Mass (volume) of solution
ppm and ppb conversions
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1 ppm = (1g/ 1x 106g) 1x 106
= (1/1000 g)
1x 106/1000g
= mg/ 1x 103 g
= mg/ L
1 ppb = (1g/ 1x 109g) 1x 109
= (1/1000000 g)
1x 109/1000000g
= mg/ 1x 103 g
= mg/ L
Effect of solutes on Solution
Properties
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Solution Properties
– a) Vapor Pressure
– b) Freezing Point
– c) Boiling Point
– d) Osmotic Pressure
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There are two types of solutes
– a) Volatile solutes (covalent)
– b) nonvolatile solutes (ionic)
Colligative properties
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“Bulk” properties that change when you
add a solute to make a solution.
• Based on how much you add but not
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what the solute is.
Effect of electrolytes is based on number of
ions produced.
Colligative properties
• vapor pressure lowering
• freezing point depression
• boiling point elevation
• osmotic pressure
Colligative Property
A
property which depends
only on the concentration or
number of solute particles
not on the nature of solutes
Vapor Pressure
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Raoult's Law
Nonvolatile solutes
Psolution = Csolvent Po(solvent)
Psolution = (1-Csolute )Po(solvent)
– vapor pressure lowering
Volatile solutes
Psolution = Ca Po(solute) + CbPo(solvent)
The vapor pressure above a
o
glucose-water solution at 25 C is
23.8 torr. What is the mole
fraction of glucose (nondissociating solute) in the
solution. The vapor pressure of
o
water at 25 C is 30.5 torr.
At a given temperature the vapor
pressures of pure liquid benzene
and toluene are 745 torr and 290
torr,respectively. A solution
prepared by mixing benzene and
toluene obeys Raoult's law. At this
temperature the vapor pressure
over a solution in which the mole
fraction of benzene is equal to
0.340 is
Benzene and toluene form an ideal
solution. At 298K, what is the
mole fraction of benzene in the
liquid that is in equilibrium with a
vapor that has equal partial
pressures of benzene and toluene?
At 298K, the vapor pressures of
pure benzene and pure toluene are
95 and 28 torr, respectively.
a) 0.50 b) 0.77 c) 0.23 d) 0.30
Boiling Point Elevation (DT)
 DTb
= Kb msolute
Kb = molal boiling point
elevation constant
 molal means concentration is
given in molality(m).
 msolute= concentration of solute
expressed as molality(m).
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What is the boiling point of a
0.500 m aqueous solution of
glucose?
(Kb for H2O is 0.512 oC/m)
DTb = Kb msolute
Freezing Point Depression (DT)
 DTf
= Kf msolute
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– Kf = molal Freezing Point Depression
constant
– molal means concentration is
given in molality(m).
– msolute= concentration of solute
expressed as molality(m).
What is the freezing point of a
0.500 m aqueous solution of
glucose? (Kf for H2O is 1.86
oC/m)
DTf = Kf msolute
A 2.25g sample of a compound is
dissolved in 125 g of benzene.
The freezing point of the solution
is 1.02oC. What is the molecular
weight of the compound? Kf for
benzene = 5.12 oC/m, freezing
point = 5.5oC.
Osmotic Pressure
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Process of solvent moving through a
semi-permeable membrane is called
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Osmosis
The pressure created by moving solvent
is called
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Osmotic Pressure
Osmotic Pressure (P)
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P = MRT
P = Osmotic pressure of the solution
M= Molarity of the solute in the solution
R = Ideal gas constant
T= Temperature of the solution in Kelvin
Calculation
Calculate the osmotic pressure in
atm at 20oC of an aqueous
solution containing 5.0 g of
sucrose (C12H22O11), in 100.0 mL
solution.
M.W.(C12H22O11)= 342.34
P = MRT
R = 0.0821 L-atm/mol K
= 62.4 L-torr/mol K
Ionic vs. covalent substances
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Ionic substances have a greater effect per
mole than covalent.
1 mol/kg of water for glucose
=1
molal
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1 mol/kg of water for NaCl
ions
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1 mol/kg of water for CaCl2 = 3 molal
ions
Effects are based on the number of
particles!
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= 2 molal
Colligative Properties of
Electrolytes
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Number of solute particles in the solution
depends on dissociation into ions expressed
as Van’t Hoff facotor(i)
Van’t Hoff facotor (i)
moles of particles in solution
moles of solutes dissolved
Colligative Properties of Electrolytes
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Vapor Pressure
 Psolution
= (1- iCsolute )Po(solvent)
Boiling Point Elevation
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DT = i Kb msolute
 Freezing Point Depression
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DT = i Kf msolute
 Osmotic Pressure
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P = i MRT
 i =Van’t Hoff factor
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Calculation
Calculate the osmotic pressure in
torr of a 0.500 M solution of
o
NaCl in water at 25 C. Assume a
100%
dissociation of NaCl.
Ideal, Negative, Positive Behavior
Predict the type of behavior (ideal,
negative, positive) based on vapor
pressure of the following pairs of
volatile liquids and explain it in terms of
intermolecular attractions:
a) Acetone/water(CH3)2CO/H2O
b) Ethanol(C2H5OH)/hexane(C6H14)
c) Benzene (C6H6)/toluene CH3C6H5.
Acetone/water(CH3)2CO/H2O
Ethanol(C2H5OH)/hexane(C6H14)
Benzene (C6H6)/toluene CH3C6H5
Define the Van't Hoff factor (i).
Which of the following solutions
will show the highest osmotic
pressure:
a) 0.2 M Na3PO4
b) 0.2 M C6H12O6 (glucose)
c) 0.3 M Al2(SO4)3
d) 0.3 M CaCl2
e) 0.3 M NaCl
5.00
M.W. = -------- = 128 g/mol
0.0391
Types of Solutions
a) True solutions
3
(diameter less than 1 x10 pm)
b) Colloids (Tyndall effect)
(range 1 x103 to 1 x105 pm)
c) Suspensions.
5
(greater than 1 x10 pm)
Tyndall Effect