Tuesday, March 12, 2013

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.
  1. 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.