Properties of Solutions

SC 132 CHEM 2 Chemistry: The Central Science

CM Lamberty

Homework Chapter 13

14, 16, 18, 20 22a, 24, 28, 30, 32, 34 36, 38, 40, 42, 44, 46, 48, 50, 52, 54 60, 64, 66, 68, 70, 72, 74, 76, 78, 86, 89, 91, 98, 112

The Solution Process The Effect of Intermolecular Forces

The Solution Process

LIKE DISSOLVES LIKESubstances with similar types of intermolecular forces dissolve in each

other.When a solute dissolves in a solvent, solute-solute interactions and solvent-solvent interactions are being replaced with solute-solvent interactions. The forces must be comparable in strength in order to have a solution occur.

Solvation: Interactions between solute and solvent molecules. Hydration: when solvent is water

Intermolecular Forces in Solution

Predicting Solubilities in Different Solvents

The Solution Process

Hsoln = Hlattice + Hhydration of ions

Hsoln = Hsolute + Hsolvent + Hmix

in ionic salt-aqueous solutions:

Hsoln < 0 means that solution formation is favored!

Why Oil and Water do not mix Give an explanation for this phenomena

based on what we have just learned.

Sol’n Formation, Spontaneity & Entropy CCl4 and C6H14 dissolve at all proportions

Similar bp, both nonpolar, similar forces Spontaneity determined by

Energy generally if E content decreases, or exothermic

Distribution of each component generally greater entropy

Entropy: the randomness or dispersal in space of the system System is no longer ordered substances

Practice

Saturated Solutions and Solubility Crystallization

Solute particles reattaching to each other Saturated

Solution in equilibrium w/ undissolved solute Solubility

Max. amt of solute that will dissolve in given amt of solvent at specific temperature

Unsaturated Less solute than needed for saturated solution

Supersaturated More solute than needed for saturated solution

Factors Affecting Solubility Solute-Solvent Interactions

The stronger the attractions between solute and solvent the greater the solubility

Like dissolves like Miscible: mix in all proportions Immiscible: do not dissolve in one another Table 13.3 Sol of alcohols in water and hexane solute-solute, solute-solvent and solvent-

solvent

Factors Affecting Solubility Pressure Effects

Solubilities of solids/liquids not affected Great effect on gases Solubility of gas increases in direct proportion

to is partial pressure above the solution Henry’s Law: Sg = kPg

Sg is solubility of gas K is Henry’s constant (solvent-solute pair dependent) Pg is partial pressure of gas over the solution

Carbonated Beverages

Factors Affecting Solubility in Liquid Solvents

Pressure Only relevant to Sgas

Sgas = kHPgas

Practice

Factors Affecting Solubility Temperature Effects

Solubility of most solid solutes in water increases as the temperature of the solution increases

Solubility of gases in water decreases with increasing temperature

Decreased O2 solubility result of thermal pollution

Factors Affecting Solubility in Liquid SolventsTemperature Ssolids increase w/temp

increase Sgases decrease w/temp

increase

Solution Concentration• Measure of the proportion of a substance

in a mixture– Units can always be expressed in fractions– Solute quantity is in numerator,

solvent/solution quantity is in denominator

• When solving problems involving solution concentration, use fraction representation of concentration unit

• UNITS, UNITS, UNITS!!!!

Concentration Term Ratio

Mass percent (m %) Mass of component in solnTotal mass of soln

Parts per millionMass of component in soln

Total mass of soln

Ways of Experessing Concentration

X 100

X 106

Parts per billionMass of component in soln

Total mass of solnX 109

Concentration Term Ratio

Molarity (M)amount (mol) of solutevolume (L) of solution

Molality (m) amount (mol) of solute

mass (kg) of solvent

Parts by massmass of solute

mass of solution

Parts by volumevolume of solute

volume of solution

Mole fraction amount (mol) of component

Total moles of all component

Ways of Experessing Concentration

Interconverting Concentration Terms To convert a term based on amount (mol) to one

based on mass, you need the molar mass. These conversions are similar to mass-mole conversions.

To convert a term based on mass to one based on volume, you need the solution density.

Molality involves quantity of solvent, whereas the other concentration terms involve quantity of solution (solvent + solute).

Practice

Practice PROBLEM: Hydrogen peroxide is a powerful oxidizing agent used in

concentrated solution in rocket fuels and in dilute solution a a hair bleach. An aqueous solution H2O2 is 30.0% by mass and has a density of 1.11 g/mL. Calculate its

(a) Molality (b) Mole fraction of H2O2 (c) Molarity

PROBLEM: A sample of commercial concentrated hydrochloric acid is 11.8M and has a density of 1.190g/mL. Calculate its

(a) Molality (b) Mole fraction of H2O2 (c) Mass %

Colligative Properties of Solutions 4 properties for which only the amount of

solute particles affect values, not chemical identity of solute Vapor pressure lowering → P = XAP°A

Boiling point elevation → Tb = kbm

Freezing point depression → Tf = kfm Osmotic pressure → = MRT

UNITS, UNITS, UNITS!!!!!

Colligative Properties of Electrolyte Solutions P, Tf, Tb, and are always greater for

an electrolyte solution with the same concentration as a nonelectrolyte one

This is because electrolyte solutions dissociate into separate pieces making the apparent solution concentration greater

Deviations from expected values can be quantified by the van’t Hoff factor, i

Practice PROBLEM: Calculate the vapor pressure lowering, P, of a solution of 2.00g of

aspirin (MM-180.15 g/mol) in 50g of methanol (CH3OH) at 21.2°C. Pure methanol has a vapor pressure of 101 torr at this temperature.

PROBLEM: You add 1.00 kg of ethylene glycol (C2H6O2) antifreeze to your car radiator which contains 4450g H2O. What are the boiling points and freezing points of the solution? (kf = 1.86°C/m and kb = 0.512°C/m for water)

PROBLEM: How many grams of NaCl must be added to a 5.00 gallon bucket filled with water (d = 1.00g/mL) to prevent the water from freezing at -10°C (kf = 1.86°C/m for water)

PROBLEM: A physician studying a particular variant of hemoglobin associated with sickle cell anemia must first determine its molar mass, which she will do by measuring its osmotic pressure. She dissolves 21.5mg of hemoglobin in water at 5.0°C to make 1.50mL of solution and measures an osmotic pressure of 3.61 torr. What is the molar mass of this variety of hemoglobin

Practice

PROBLEM: A 0.952-g sample of magnesium chloride is dissolved in 100. g of water in a flask.

(a) Which scene depicts the solution best?

(b) What is the amount (mol) represented by each green sphere?

(c) Assuming the solution is ideal, what is its freezing point (at 1 atm)?

PROBLEM: The MgCl2 in the above problem has a density of 1.006g/mL at 20.0°C. What is the osmotic pressure of the solution?

Colloids Intermediate type of dispersion or

suspension Dividing line between solutions and

heterogeneous solutions Size of dispersed particle 5-1000nm May be several atoms/ions or one large

one Scatter light Homogenized milk

Colloids Hydrophilic and Hydrophobic Colloids

Hydrophilic (water loving) Hemoglobin, enzymes and antibodies Molecules fold so that hydrophobic groups on inside

away from water Hydrophobic (water fearing)

Must be stabilized in water Adsorption of ions on sfc Oil slick on water Bile from gallbladder helps digest fats (emulsify the

fat)

Colloids Removal

Filtration will not work Coagulation: process by which the particles

clump together Semipermeable membranes

Dialysis