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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.

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Properties of Solutions

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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 LIKE

Substances 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

DHsoln = DHsolute + DHsolvent + DHmix

in ionic salt-aqueous solutions:

DHsoln = DHlattice + DHhydration of ions

DHsoln < 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 Solvents

Temperature

  • 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!!!!


Mass of component in soln

Mass percent (m %)

Total mass of soln

Mass of component in soln

Mass of component in soln

Parts per million

Parts per billion

Total mass of soln

Total mass of soln

Ways of Experessing Concentration

Concentration Term

Ratio

X 100

X 106

X 109


amount (mol) of solute

Molarity (M)

volume (L) of solution

amount (mol) of solute

Molality (m)

mass (kg) of solvent

mass of solute

Parts by mass

mass of solution

volume of solute

Parts by volume

volume of solution

amount (mol) of component

Mole fraction 

Total moles of all component

Ways of Experessing Concentration

Concentration Term

Ratio


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


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

PROBLEM:

Practice

(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, DP, 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.

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:

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


PROBLEM:

PROBLEM:

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

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?

(a) Which scene depicts the solution best?

Practice

(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)?


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


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