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