SOLUTIONS AND THEIR PHYSICAL PROPERTIES

TYPES OF SOLUTIONS

Solution: A homogenous mixture whos properties are uniform and which contains two or more substances that can be varied

Solvent: The component that is present in the greatest quantity or that determines the state of matter in which the solution exists.

Solute: A solution component that is present in a solution in lesser quantity than the solvent.

Concentrated solution: Solutions containing a relatively high concentrations of solute. Diluted solution: Solution containing a relatively low concentrations of solute.Solubility: The max. amount of the solute that will dissolve in a definite amount of the

solvent and produce a stable system at a specified temperatureSaturated solution: When dissolving and precipitation occur at the same rate, the

quantity of dissolved solute remains constant with time and the solution is said to be saturated.

Supersaturated solution: The solution in which the concentration of solute is higher than that of a saturated solution.

Alloy: Solid solutions with a metal as the solvent ; e.g. brass (Cu-Zn), solder (Sn-Pb)

Some Common Solutions

SOLUTION SOLUTE

GaseousGaseous LiquidLiquid SolidSolid

SOLVENT

GaseousGaseous Air(N2+O2+several others)

LiquidLiquid Mineral water( CO2 in water)

Alcohol(Ethanol)-water, Polyhydrocarbon-gasoline

NaCl in water, Au in Hg

SolidSolid Pt/ H2 Mercury in Gold,Hexane in paraffin

Bronze(Cu-Sn)Brass(Cu-Zn)

Solution ConcentrationA measure of the quantity of the solute present in a given quantity of solvent is called concentration denir. Concentration can be explained in many ways using expressions such as saturated, unsaturated, supersaturated, diluted or concentrated solution. Besides, it can be expressed also with some terms of quantity such as, molarity, ppt, ppm ve ppb, molality, normality. In addition, some other definition such as mole fraction, mole percentage can be used.

Mass Percent, Volume Percent, and Mass/Volume Percent

Mass percentage % (m/m) = msolute/msolution

If we dissolve 5,00 g NaCl, in 95 g water , we get 100 g of a solution that is % 5,00 NaCl .

% Volume (V/V) = Vsolute/Vsolution

25,0 mL methyl alcohol and 75,0 mL water is an antifreeze solution that is % 25,0 CH3OH by volume.

Mass/Volume % (m/V) = msolute/Vsolution

An aqueous solution with 0,9 g NaCl in 100 mL of solution is said to be % 0,9 (mass/volume).

Solution Concentration

Mole Fraction and Mole Percent

Mol fractionAmount of component (in moles)

t

ii n

n

Total amount of all solution components( in moles)

Mole percent 100% t

ii n

n

Molarity ve Molality

MolarityAmount of solute (in moles)

solution

solute

V

nM

Volume of solution (L)

MolalityAmount of solute (in moles)

solvent

solute

m

nM

Mass of solvent ( Kg )

Illustrative ExamplesThe concentration of a solution in different units:

An ethanol-water solution is prepared by dissolving 10,00 mL of C2H5OH (d=0,789 g/mL) in a sufficient volume of water to produce 100 mL of a solution with a density 0,982 g/mL. What is the concentration of ethanol in this solution as (a) volume percent (b) mass percent (c) Mass/Volume percent (d) mole fraction(e) mole percent(f) molarity(g) molality?

ethanol89,7ethanol mL 1

ethanol789,000,10ethanol g

gmLm b)

a) 00,10%100solution mL 100,0

ethanol00,10(volume) ethanol%

mL

solution2,98solution mL 1

solution982,0solution0,100solution g

gmLm

03,8%100solution g 98,2

ethanol89,7m)ethanol(m/%

g

Illustrative Examples

c) 89,7%100solution mL 100,0

ethanol89,7(m/V) ethanol%

g

d) Convert the mass of ethanol from part b) to an amount in moles

OHHCmolOHHC

OHHCmolOHHCgn 52

52

5252ethanol 171,0

g46,07

189,7

If 100,0 mL solution weighs 98,2 g ; 98,2 - 7,89 = 90,3g water.

OHmolOH

OHmolOHgn 2

2

22water 01,5

g02,81

13,90

0330,001,5HC mol0,171

HC171,0

252

52ethanol

OHmolOH

OHmol

Mole Fraction of Ethanol

SOLUTION CONCENTRATION

e) Mole Percent of Ethanol = 30,3%100ethanol

OHHCMOH

OHHCmolM 52

2

52 71,1L1,0

171,0f)

g) OHkgOH

OHkgOHgkgmwater 2

2

22 0903,0

g1000

13,90)(

“Molality of Ethanol”

OHHCmOHg

OHHCmolM 52

2

52 189,0k0903,0

171,0

m: molality (mol/kg)

INTERMOLECULAR FORCES AND THE SOLUTION PROCESS

In this section we focus on the behaviour of molecules in solution, specifically on intermolecular forces

I. aşama

II. aşama

III. aşama

ΔHsoln= 0

Pure solvent seperated solvent molecules ΔHa >0

Pure solute seperated solute molecules ΔHb >0

Seperated solvent and solid molecules solution ΔHc <0

ΔHsoln= ΔHa+ ΔHb + ΔHc

INTERMOLECULAR FORCES IN MIXTURES

• The values ΔHa, ΔHb, and ΔHc depend on the strengths of intermolecular forces of attraction

• If all intermolecular forces of attraction are of about equal strength, a random of intermingling of molecules occurs. A homogenous mixture or solution results and this is called as ideal solutionsideal solutions.

• ΔHa + ΔHb ~ -ΔHc ΔHsoln ~ 0,

Intermolecular forces between:

ΔHa = solvent molecules A

ΔHb = solute molecules B ,

ΔHc = solvent molecules A and solute molecules B (A-B)

IDEAL SOLUTIONS

Substances with similar molecular structures have similar intermolecular forces of attraction. Example: The solution of the liquid hydrocarbons (Benzene- Toluene mixture). ΔHsoln ~ 0 .

NONIDEAL SOLUTIONS

• If forces of attraction between same molecules, A-A or B-B (molecules between solvent or solute), are SMALLER, than forces of attraction of unlike molecules A-B, (forces between solute and solvent), a solution is formed but its properties can not be predicted. These are identified as non-ideal solutions. Interactions between solute and solvent(ΔHc) release more heat than the heat

absorbed to seperate the solvent and solute molecules (ΔHa + ΔHb). The work of

solubility is an exothermic reaction (ΔHsoln <

0).

A-A < A-BOR

B-B < A-B

CHCl3 Chloroform -- (CH3)2CO Acetone

(CH3)2CO Acetone ----- CS2 Carbon disulfide(Polar-Non polar solution)

• If forces of attraction between same molecules, A-A or B-B (molecules between solvent or solute), are ONLY A LITTLE GREATER, than forces of attraction of unlike molecules A-B, (forces between solute and solvent), a NON-IDEAL solution is formed as a complete mixture. The solution has a higher enthalpy(ΔHc) than the pure

componentsΔHa+ ΔHb); so the solution

process is endothermic (ΔHsoln > 0).

A-A > A-Bveya

B-B > A-B

NONIDEAL SOLUTIONS

NONIDEAL SOLUTIONS

• If forces of attraction between same molecules, A-A or B-B (molecules between solvent or solute), are MUCH GREATER, than forces of attraction of unlike molecules A-B, (forces between solute and solvent), dissolving does not occur to any siginificant extent. The components remain segregated in a heterogenous mixture. In a mixture of water and octane( a constituent of gasoline) strong hydrogen bonds hold water molecules together in clusters. The non-polar octane molecules are not able to exert a strong attractive force on the water molecules, and two liquids do not mix.

A-A >> A-Bor

B-B >> A-B

Water molecules

Octane molecules

Strong H bonds

IONIC SOLUTIONS

• If the ion-dipole forces of attraction are strong enough to overcome the interionic forces of attraction in the crystal, dissolving will occur. An ion surrounded by a cluster of water molecules is said to be hydrated.

KCl(s) K+(g) + Cl-(g) ΔH1=(- lattice energy of KCl)=701,2 kJ

K+(g) + Cl-(g) K+(aq) + Cl-(aq) ΔH2= - 684,1 kJ

ΔHf= ΔH1 + ΔH2= 17,1 kJ

a)Diluted b)Concentrated c)Saturated

SOLUTION FORMATION AND EQUILIBRIUM

• When the solute and the solvent are mixed up;

• a) First dissolving occur,

• b) Then precipitation starts and increases with time

• c) After a while the dissociation and precipitation rates become equal.The quantity of dissolved solid remains constant with time

• These solutions are called as saturated solutions

• The concentration of the saturated solution is called the solubility of the solute in the given solvent . It can be expressed as Molarity or Mass Percent

• Solubility varies with temperature.

SOLUTION FORMATION AND EQUILIBRIUM

• If in preparing a solution we start with less solute than would be present in the saturated solution, the solution is unsaturated.

• The precipitation occurs when a saturated solution is cooled.

• Occasionally all the solute may remain in the solution(as at that temperature the solvent dissolves a greater amount of solute than that in the saturated solution) We identify these solutions as supersaturated solutions.

• KNO3 dissolves in 100 g water and 30oC at an amount of ~32g .This solution is saturated. At the same temp., if 30g KNO3 are dissolved, it is unsaturated, 35g KNO3 are dissolved, it is supersaturated. Solubility Curve for various substances

SOLUTION FORMATION AND EQUILIBRIUM

• The solubilities of ionic substances increaseincrease with increasing temperature increasing temperature Exceptions to this generalization are:SO3

2-, SO42-, SeO4

2-, AsO43-, PO4

3- .

• When Hsoln > 0, raisingraising the temperature increasesincreases the solubility.

• When, Hsoln < 0, the solubility

decreasesdecreases with increasing increasing temperature.

• We prepare a concentrated solution at a high temperature. Then we let the solution cool. At lower temperatures the solution becomes saturated in the desired compound. The excess compound crystallizes from solution and the impurities remain in solution. This method of purifying a solid called fractional crystallisation.

SOLUBILITY OF GASES

• Effect of Temperature In a gas, the molecules are much farther apart than they will be in the solution(solid-liquid mixtures). Hence, the gas must condense to a liquid before it dissolves in another liquid. Condensation is an exothermic reaction and “The solubilities of gases decrease with increased temperature”. Ex: Beverages which contain CO2 are consumed cold. Fish require cold watersince there is not enough dissolved air(oxygen) in hot water

• Effect of Pressure

The solubility of a gas increases as the gas pressure is increased.This is called Henry’s law. C = solubility of gas mL/Lk = proportionality constant

gasPkC If the gas pressure increases, the

solubility rises

Henry’s Law fails for gases at high pressures and it also fails if the gas ionizes in water or reacts with water.

We only expect Henry’s law to apply to equilibrium between molecules of a gas and the same molecules in solution

Solubility: The amount of gas which is able to dissolve at 0oC and 1 atm pressure in 1 L water.

SOLUBILITY OF GASES

Example: At 0oC and 1 atm pressure N2 gas has the solubility of 23,54 mL N2/L. in order to reach a solubility of 100,0 mL N2 per liter, what pressure must be exerted at 0oC?

2

/0,100

00,1

/54,23 22

Ngaz P

LNmL

atm

LNmL

P

Ck atmPN 25,4

2

Example: At 0oC and O2 pressure of 1,00 atm, the aqueous solubility of O2(g) is 48,9 mL O2/L. What is the molarity of O2 in a saturated water solution when the O2 is under its normal partial pressure in air (0,2095 atm)?

Molarity of O2 at 0oC and 1 atm

242

3

1057,42095,000,1

1018,2OMC

atm

C

atm

OM

P

Ck

gaz

232

22

1018,21

)(4,221

0489,0

2OM

SolutionLNKOL

OmolOL

MO

VAPOR PRESSURES OF SOLUTIONS

Fractional Distillation

We find the vapor pressures of solutions to be important when we want devise a method of seperating volatile liquid mixtures by distillation. Also, boiling point and osmotic pressure play an important role in the fractional distillation. In 1880, the French chemist Raoult found that a dissolved solid lowers the vapor pressure of the solvent.

The partial pressure exerted by solvent vapor above an ideal solution, PA, is the vapor pressure of the pure solvent at the given temperature PA

o, multiplied by the mole fraction of the solvent in the solution, XA

oAAA PP Raoult’s Law:

VAPOR PRESSURES OF SOLUTIONS

Predicting Vapor Pressures of Ideal Solutions: The vapor pressures of pure benzene and toluene at 25 oC are 95,1 ve 28,4 mmHg. A solution is prepared in which the mole fractions of benzene and toluene are both 0,500. What are the partial pressures of benzene and toluene in this solution? What is the total pressure? What is the composition of the vapor of benzene-toluene at equilibrium ?

230,08,61

2,14

770,08,61

6,47

8,61

2,146,47

2,144,28500,0

6,471,95500,00

0

mmHg

mmHg

P

P

mmHg

mmHg

P

P

mmHgP

mmHgmmHgP

mmHgmmHgPP

mmHgmmHgPP

top

toltol

top

benzbenz

top

top

toltoltol

benzbenzbenz

Composition of solution

Composition of vapor

LIQUID-VAPOR EQUILIBRIUM: IDEAL SOLUTIONSThe line combining the 3 - 4 points is called “tie line”. The vapor ends of these ties lines can be joined by the green curve. From the relative placement of the liquid-vapor curves we see for ideal solutions of two components, the vapor phase is richer in the more volatile component than is the liquid phase.

500,0ben

When this solution is again vaporized;

The process of re-vaporisation and condensation can be continiued. This is called fractional distillation.

Comp. of Vapor

920,0ben080,0tol

500,0benComposition of Solution

500,0tol

Comp. of Vapor770,0ben230,0tol

LIQUID- VAPOR EQUILIBRIUM:NONIDEAL SOLUTIONS

Propanol-Water Azeotrope Mixture contains 71,69% propanol and 28,31% water.

In nonideal solutions, if the departures from ideal solution behaviour are sufficiently great, certain solutions may vaporize to produce a vapor that has the same composition as the liquid. These solutions, called azeotropes boil at a constant temperature and because the liquid and vapor have the same composition, they can not be seperated by fractional distillation

LIQUID-VAPOR CURVES IN AZEOTROPE MIXTURES

Ethyl alcohol-water azetrope mixture has the boling point of 78,2˚C with the composition 95.6% ethyl alc. and 4.4% water

Freezing Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions

The properties such as Vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure whose values depend only on the concentration of solute particles in solution and not on what the solute is, are called colligative properties.

mKT FPFP Freezing point depression

FPFPFP TTT 0

mKT BPBP Boiling point elevation

0BPBPBP TTT Temperature

fp fp0

ΔTFP

bp0 bp

ΔTBP

Establishing a molecular formula with freezing point data: Nicotine, extracted from tobacco leaves, is a liquid completely miscible with water at temperatures below 60 oC . (a)What is the molality of nicotine in an aqueous solution that starts to freeze at -0,450 oC ? (b) If the solution is obtained by dissolving 1,921 g of nicotine in 48,92 g of water, what must be the molar mass of nicotine? KFP=1,86 oC/m

a)

mCC

K

Tm

mC

FP

FP 242,086,1

)450,0(0

b)

waterkg

mol

waterkg

MAg

m

nm ineni

water

242,004892,0

/921,1 cot

molgmol

gMA ineni /162

)242,004892,0(

921,1cot

Freezing Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions

OSMOTIC PRESSURE

An aqueous sucrose(sugar) solution in a long glass tube is seperated from pure water by a semipermeable membrane(permeable to water only). Water molecules can pass through the membrane in either direction. But because the concentration of water molecules is greater in the pure water than in the solution, there is a net flow from the pure water into the solution. This net flow called osmosis, causes the solution to rise up the tube.

Applying a pressure to the sucrose solution slows down the net flow of water into the solution. The necesssary pressure to stop osmotic flow is called the osmotic pressure and represented by the symbol . This pressure is 15 atm for a 20% sucrose solution. Osmotic pressure is a colligative property because its magnitude depends only on the number of solute particles per unit volume of solution

TRc

TRV

n

Osmotic Pressure ()

R(gas constant) = 0,08206 L atm/(mol K)

c = Molarity of the solution

OSMOTIC PRESSURE

Calculating osmotic pressure: What is the osmotic pressure at 25 oC of an aqueous solution that is 0,0010 M C12H22O11 (sucrose)?

)18(024,01

298)/(08206,00010,0mmHgatm

L

KKmolatmLmol

Establishing a molar mass from a measurement of osmotic pressure: A 50,00 mL sample of an aqueous solution is prepared containing 1,08 g. of a blood plasma protein, human serum albumin. The solution has an osmotic pressure of 5,85 mmHg at 298 K. What is the molar mass of the albumin?

atmmmHg

atmmmHgPalb

31070,7760

185,5

V

mRTMA

V

RTMAm

)/(

molgL

KKmolatmLgMAalb /1086,6

050,01070,7

298)/(08206,008,1 43

Freezing Point Depression and Boiling Point Elevation of Electrolyte Solutions

Some solutes produce a greater effect on colligative properties. For example consider a 0,0100 m aqueous solution. The predicted freezing point depression of this solution is

If the 0,0100 m solution is urea, the measured freezing point is just -0,0186, if the solution is 0,0100 m NaCl (electrolyte), the measured freezing point is -0,0361. The ratio of the measured value of a colligative property to the expected value, if the solute were electrolyte is called Van’t Hoff factor (i) .

CmmCmKT FPFP 0186,00100,0/86,1

292,10186,0

0361,0

)(

)(

exp

C

C

T

Ti

ectedFP

measuredFP

Van’t Hoff factor

For a non-electrolyte i = 1

NaCl i = 2

MgCl2 i = 3

Equations of Colligative Properties for some electrolytes

mKiT FPFP

mKiT BPBP

TRci

Freezing Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions

Predicting Colligative Properties for electrolyte solutions: Predict the freezing point of aqueous 0,00145 m MgCl2 . KFP = 1,86 oC/m

MgCl2 (aq) Mg2+(aq) + 2Cl-

(aq) Van’t Hoff factor, i = 3

CT

mmCT

mKiT

FP

FP

FPFP

0081,0

00145,0/86,13

REVERSE OSMOSIS-DESALINATION

In this case, the membran is only permeable for the water molecules. Under normal conditions in the event of OSMOSIS , there is a net flow from the pure water to the salty water. When a pressure is applied on side B (P> Pos), a net flow of water from salty water to the pure water occurs. This is called REVERSE OSMOSIS . By means of DESALINATION, pure water can be obtained from seawater and other waste water can be reused by this way .

Practical Applications -FP lowering

Salt can be used to deice roads.

Automobile antifreeze ethylene glycol (C2H4(OH)2)