Chemistry 102(01) Spring 2002 Instructor: Dr. Upali Siriwardane e-mail:upali@chem.latech 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, 2002 (Test 1): Chapter 12 &13. April 26, 2002(Test 2): Chapter 14 & 15. May 15, 2002 (Test 3): Chapter 15 & 17. May 16, 2002 (Comprehensive Test): Chapters 12,13,14,15,17

Chapter 12. Physical Properties of Solutions

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 dissolves like.”Like dissolves like.” Materials with similar polarity are soluble

in each other. Dissimilar ones are not. MiscibleMiscible Liquids that are soluble in each other in

all proportions such as ethanol and water. ImmiscibleImmiscible Liquids that are not soluble in each other

such as hexane and water.

Solubility of Salts

SOLUBILITY RULES

SOME SALTS ARE SOLUBLE

SOME ARE INSOLUBLE

THERE ARE DEGREES OF SOLUBILITY

Amount of Solute A 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

Miscibility of solute and solvent-

”Like dissolves like” Heat of solution, H(solution)

exothermic -cooling helps endothermic-heating helps

Gases:cooling & pressure helps

Identify Polar and Non-polar groups in Covalent Molecules

Acetic acidHC2H3O2

CH3COOH

HexanolC6H13OH

HexaneC6H14

Propanoic acidC2H5COOH

Like Dissolves Like

Solution Process of Ionic Compounds

Temperature and solubility

0

100

200

300

0 20 40 60 80 100

SO2

KClglycineNaBrKNO3

sucrose

Solu

bili

ty(g

/100

ml w

ate

r)

Temperature (oC)

Pressure and solubility of gases Increasing the pressure of a gas above a

liquid increases the concentration of the gas.

This shifts the equilibrium, driving more gas into the liquid.

Henry's law 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. S1/S2 =p1/p2

Electrolytes

Solutes which dissolves in water to form conducting solution- Electrolytes

Solutes which dissolves in water to from non-conducting solution-Non- Electrolytes

Solutes which dissolves in water to from weakly conducting solution -Weak- Electrolytes

Concentration Units

a) Molarity (M) b) Normality (N) c) Molality (m) d) Mole fraction (a) e) Mass percent (% weight) f) Volume percent (% volume) g) "Proof" h) ppm and ppb

Molarity(M)

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)

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 20oC. The density of C2H5OH is 0.789 g/mL.

Mole fraction (a)

moles of solute (substance) a = ------------------------------------- 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 %

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 %

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)

Mass (volume) of solute ppm = -------------------------------- x 106 Mass (volume) of solution Mass (volume) of solute ppb = -------------------------------- x 109

Mass (volume) of solution

ppm and ppb conversions 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 = g/ 1x 103 g = g/ L

Effect of solutes on SolutionProperties Solution Properties

– a) Vapor Pressure– b) Freezing Point– c) Boiling Point– d) Osmotic Pressure

There are two types of solutes– a) Volatile solutes (covalent)– b) nonvolatile solutes (ionic)

Colligative properties “Bulk” properties that change when you

add a solute to make a solution.

• Based on how much you add but not– what the solute is.

• Effect of electrolytes is based on number of ions produced.

Colligative propertiesColligative 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

Raoult's Law Nonvolatile solutes

Psolution =solvent Po(solvent) Psolution =solute )Po(solvent)

– vapor pressure lowering Volatile solutes

Psolution = aPo(solute) +bPo(solvent)

The vapor pressure above a glucose-water solution at 25oC is 23.8 torr. What is the mole fraction of glucose (non-dissociating solute) in the solution. The vapor pressure of water at 25oC 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 (T)

Tb = Kb msolute

Kb = molal boiling point elevation constant

molal means concentration is given in molality(m).

msolute= concentration of solute expressed as molality(m).

What is the boiling point of a 0.500 m aqueous solution of glucose? (Kb for H2O is 0.512 oC/m)

Tb = Kb msolute

Freezing Point Depression (T) Tf = Kf msolute

– 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)

Tf = 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

Process of solvent moving through a

semi-permeable membrane is called

Osmosis

The pressure created by moving solvent

is called

Osmotic Pressure

Osmotic Pressure (

= MRT = Osmotic pressure of the solution M= Molarity of the solute in the solution R = Ideal gas constant T= Temperature of the solution in Kelvin

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

= MRT R = 0.0821 L-atm/mol K = 62.4 L-torr/mol K

Calculation

Ionic vs. covalent substances

Ionic substances have a greater effect per mole than covalent.

1 mol/kg of water for glucose = 1 molal

1 mol/kg of water for NaCl = 2 molal ions

1 mol/kg of water for CaCl2 = 3 molal

ions Effects are based on the number of Effects are based on the number of

particles!particles!

Colligative Properties ofElectrolytes

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 Vapor Pressure

Psolution = (1- isolute )Po(solvent) Boiling Point Elevation T = i Kb msolute Freezing Point Depression T = i Kf msolute

Osmotic Pressure = i MRT i =Van’t Hoff factor

Calculate the osmotic pressure in torr of a 0.500 M solution of NaCl in water at 25oC. Assume a 100%dissociation of NaCl.

Calculation

Predict the type of behavior (ideal, negative, positive) based on vapor pressure of the following pairs ofvolatile liquids and explain it in terms of intermolecular attractions: a) Acetone/water(CH3)2CO/H2Ob) Ethanol(C2H5OH)/hexane(C6H14) c) Benzene (C6H6)/toluene CH3C6H5.

Ideal, Negative, Positive BehaviorIdeal, Negative, Positive Behavior

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

5.00M.W. = -------- = 128 g/mol 0.0391

a) True solutions (diameter less than 1 x103  pm)b) Colloids (Tyndall effect) (range 1 x103  to 1 x105 pm) c) Suspensions. (greater than 1 x105 pm)

Types of Solutions

Tyndall Effect