COLLIGATIVE PROPERTIES

COLLIGATIVE PROPERTIES OF SOLUTIONS

1.    Colligative Properties depend on the concentration of solute in solvent and not upon the identity of the solute.

a.    Vapor pressure reduction is a colligative property in which the pressure of the vapor over a solvent is reduced when a nonvolatile solute dissolved in the solvent.  It is directly proportional to the concentration of a solution.

b.    Boiling Point Elevation is a colligative property in which the boiling point of a solvent is raised when a nonvolatile solute is dissolved in the solvent.  It is directly proportional to the concentration of a solution.

c.    Freezing point depression is a colligative property in which the freezing point of a solvent is lowered by the addition of a solute.

d.    Osmotic pressure is the force that makes osmosis possible.

2.    The gas pressure resulting from the vapor molecules over the liquid is the vapor pressure.

3.    Boiling Point is the temperature at which the vapor pressure of a liquid becomes equal to the atmospheric pressure.

4.    Osmosis refers to the movement of solvent through a semi permeable membrane from a region of higher concentration to a region of lower concentration.

5.    The most commonly used measurements of concentration are molarity, molality and mole fraction.

Boiling Point elevation	Freezing Point Depression
Tb= Kbm Where: Tb= boiling point elevation (oC)           Kb= molal boiling point elevation constant   of solvent (oC/m) m= molality (m)	Tf= Kfm Where: Tf= freezing point depression (oC) Kb= molal boiling point elevation constant of solvent (oC/m) m= molality (m)

Vapor pressure Reduction	Osmotic pressure
Pa= XaPoa Where: Pa= vapor pressure lowering of solution Xa=  mole fraction of solute Poa=  vapor pressure of pure solvent Units of pressure: mmHg, atm, Pa, torr,	π=MRT Where:   ¶=  osmotic pressure in atm                M=        Molarity (mol/L)                R= 0.0821 L atm/mol K                T=  temperature in Kelvin         K=  oC + 273

2014 4th Quarter : DILUTION WORKSHEET

Dilutions Worksheet - Solutions

1)        If I add 25 mL of water to 125 mL of a 0.15 M NaOH solution, what will the molarity of the diluted solution be?

M₁V₁ = M₂V₂

(0.15 M)(125 mL) = x (150 mL)

x = 0.125 M

2)        If I add water to 100 mL of a 0.15 M NaOH solution until the final volume is 150 mL, what will the molarity of the diluted solution be?

M₁V₁ = M₂V₂

(0.15 M)(100 mL) = x (150 mL)

x = 0.100 M

3)        How much 0.05 M HCl solution can be made by diluting 250 mL of 10 M HCl?

M₁V₁ = M₂V₂

(10 M)(250 mL) = (0.05 M) x

x = 50,000 mL

4)        I have 345 mL of a 1.5 M NaCl solution.  If I boil the water until the volume of the solution is 250 mL, what will the molarity of the solution be?

M₁V₁ = M₂V₂

(1.5 M)(345 mL) = x (250 mL)

x = 2.07 M

5)        How much water would I need to add to 500 mL of a 2.4 M KCl solution to make a 1.0 M solution?

M₁V₁ = M₂V₂

(2.4 M)(500 mL) = (1.0 M) x

x = 1200 mL

            1200 mL will be the final volume of the solution.  However, since there’s already 500 mL of solution present, you only need to add 700 mL of water to get 1200 mL as your final volume.  The answer:  700 mL.

4th Quarter 2012-2013: COLLOIDS HANDOUT

COLLOIDS

Mixtures are either homogeneous or heterogeneous, but sometimes the distinction is not easily made.  These are the systems that appear homogeneous to the naked eye but are actually heterogeneous.  These are the colloids.

Colloidal particles are larger than those of the solution but smaller than those of the suspension.  ( 1nm to 100 nm)

glue-like”, Greek word for glue is Kolla, for like it is eidos.

Thomas Graham is the Father of Colloidal Chemistry.

All colloidal systems have two components; the dispersed phase, the substance that is suspended, and the dispersion medium, the substance in which another substance is suspended.

For the formation of colloids, the dispersed phase and the dispersion medium must be mutually insoluble.

There are two classification of colloids based on the degree of attraction between the dispersed phase and the dispersion medium.  Colloids in which the attraction between the dispersed phase and the dispersion medium.  Colloids in which the attraction is strong are called lyophilic (solvent-loving), and those in which there is very little attraction or no attraction at all are called lyophobic (solvent-hating)

Classifications of Colloidal Systems

Phase of Colloid	Dispersion Medium	Dispersed Phase	Colloid	Examples
Gas	Gas	Gas	-	-
Gas	Gas	Liquid	Liquid aerosol	Fog
Gas	Gas	Solid	Solid aerosol	Smoke
Liquid	Liquid	Gas	Foam	Whipped cream
Liquid	Liquid	Liquid	Emulsion	Milk
Liquid	Liquid	Solid	Sol	Paint
Solid	Solid	Gas	Solid foam	Marshmallow
Solid	Solid	Liquid	Solid emulsion	Butter
Solid	Solid	Solid	Solid sol	Ruby glass

1. Solid emulsion
• lyophilic colloids

Examples: 

                         Jellies, gel, slimy precipitate of aluminum hydroxide, protoplasm

                                    Application:  

Syneresis - skin gets wrinkled as one gets older, Separation of serum from blood clot and sweating of butter.

2. Emulsion

lyophobic colloids

An emulsion is a colloid that contains tiny droplets of a liquid dispersed in another liquid.  It is formed only in the presence of a substance called emulsifying agent that helps disperse tiny particles of one liquid to another.

Oil and water in mayonnaise will not mix normally.  But in the presence of egg yolk intimately mixed with them, oil and water will not separate.

prepared by shaking two immiscible liquids

            Emulsifying agent/ stabilizing agent/ protective colloids

a substance used to make or form an emulsion

                                    Example: 

Milk- casein

                                                Mayonnaise- egg yolk

                                                Oil and water- soap

                                    Application: 

Removing dirt using soap

Preparation of Colloidal System

The dispersion method of preparing colloids involves is the breaking down of large particles into colloidal size.

Grinding - a colloid mill is used (preparation of paint pigments or face powders)

beating, stirring, whipping -  examples:  mayonnaise, creams

Peptization - chemicals are used to break down big particles (NaOH, sodium hydroxide is used to break up clay, glue, starch).  Gelatin peptized in water

homogenizing

using an emulsifying agent

     2.  The condensation method involves the clustering of small particles into colloidal size.  This is accomplished by chemical reactions in which the starting materials are in true solutions.

Carbon black is prepared by burning methane in limited air and collecting the soot or carbon atoms on cool surfaces.  Carbon black is used as filler for rubber tires and in dispersions such as printers ink and Indian ink

favorable weather conditions can lead to formation of clouds, fogs and mists

Properties of colloidal systems

A colloidal system is a two-phased mixture with particles that are not large enough to be seen by an ordinary microscope but big enough to diffuse light, giving a Tyndall Effect.

Colloidal systems manifest five properties that distinguish them from the true solutions and suspensions.  These properties are:

a.) Tyndall Effect – ability of colloidal particles to scatter a beam of light that passes through them.  (John Tyndall)

                        Applications:

blue color of the sky and sea

brilliant colors of  sunset

of different shades or even blue and violet colors are obtained with different sizes of dispersed gold particles

different colors of your eyes and those of other people are not due to pigments, but rather to the scattering of light by colloidal substance in the iris

            b.)  Adsorption - a surface property

the ability of a substance to physically hold another substance on its surface

                                                            Absorption vs. Adsorption (laboratory results)        

the greater the surface area, adsorption increases

colloids make good adsorbers

                        Applications:

Toxic hydrocarbons accumulate on the surface of asbestos particles.  For this reason, asbestos is more hazardous when inhaled than when ingested.  The same reason may apply to smoking marijuana.  The smoke particles carry along with it more toxic compounds.

Activated carbon is widely used to remove objectionable odors and colors in foods or chemical products and to eliminate contaminating gases such as oil vapor and sulfur dioxide from industrial gases like Hydrogen, acetylene, CO₂ and CO.  The sugar industry uses large quantities of activated carbon in refining.  Similarly the activated carbon is used in refining corn syrup and corn sugar. Low boiling petroleum components are recovered by fractional adsorption with gas adsorbing carbon.  The military utilizes activated carbon in gas masks.

Filtration plants also treat the domestic water supply with activated carbon to remove unpleasant odor, color and taste.

Piece of charcoal can put inside the refrigerator to remove unpleasant odors.

Cigarette filters contain activated charcoal to remove carcinogenic compounds from tobacco smoke.

c.) Electrical Charge Effect – the positive or negative charge acquired by colloidal particles due to the ions adsorbed on their surface.

What causes the colloidal particles to carry a charge?  Colloid particles, because of their high adsorptive capacity, adsorb on their surface ions from water or from solutions of electrolytes.  A given kind of colloid adsorb on its surface only one kind of ions, hence the particles become either all negative or all positive.

Electrophoresis - the movement of charged colloidal particles toward the electrodes.

Example: clay and water

Clay becomes negative in water because it adsorbs the hydroxyl ion (OH^–1).  Since all the particles in a colloid have the same charge, they repel each other.  This is the principal reason why colloidal particles do not aggregate or precipitate.

  

Applications:

Electrodeposition of rubber latex into anodes of various shapes e.g. tires, gloves, etc.

in industry, electrostatic precipitates are used to remove colloidal particle pollutants from smoke (Cottrell precipitator)

d.) Brownian Movement - rapid zigzag movement of colloidal particles.  (Robert Brown)

The zigzag movement of colloidal particles is caused by unequal number of collisions of colloidal particles on different sides of the molecules.  This property of colloidal system explains why colloidal particles do not settle.

Applications:

Formation of fogs, mist and smog.  Traveling becomes dangerous.  Too much colloid in the air also endangers a person’s health.  Colloidal particles in the air contributes to the air pollution problems

e.)  Rate of Settling - dependent on the size of particles, the gravitational force acting on the colloidal particles and the viscosity of the medium.

Applications: 

The above factors are useful in identifying viruses, proteins, plastics and other macromolecules.

Importance of Colloids to Daily Life

Colloid chemistry is important in the manufacture of paint, ceramics, plastics, textile, glue, adhesive, ink, cement, rubber, leather, photographic paper and film, salad dressing, spray, detergent, and many more. 

It is also involved in processes like bleaching, deodorizing, tanning, dyeing, and purification and flotation of minerals.

The protoplasm of living cells and tissue, most of the body fluids, glandular secretions, blood, and many foods are colloidal substances.  Thus, the essential vital processes – nutrition, digestion, and secretion – are concerned with colloidal systems.

Dialysis – is the process of separating ions from colloids by diffusion through a semi permeable membrane.