COLLOids

Aqueous &Non-aqueous Solutions

Aqueous Solutions

Solutions that contain water as the solvent .

For example:

sugar in water, carbon dioxide in water, etc .

Non-aqueous Solutions

Solutions that contain solvent other than water . Ether, benzene, petrol, carbon tetrachloride etc., are some common solvents.

For example :

sulphur in carbon disulphide, naphthalene in benzene, etc .

Concentrated Solutions and Dilute Solutions

The concentration of a solution is expressed as the amount of solute present in a given amount (mass or volume) of the solution; or the amount of solute dissolved in a given mass or volume of a solvent. It is expressed as a percentage of

these quantities .

Between two solutions, the solute quantity may be relatively more or less. If the proportion of solute is less, the solution is said to be dilute.

Solutions True Solutions:

A true solution is a homogeneous solution in which the solute particles have diameters between 0.1 nm to 1 nm i.e., the solute particles are of molecular dimensions.

Such dispersed particles dissolve in solution to form a homogenous system. These do not settle down when the solution is left standing. The particles are invisible even under powerful microscopes and cannot be separated through filter paper ,parchment paper or animal membranes. For example, sodium chloride in water is a true solution. Most ionic compounds form true solutions in water. Organic compounds like sugar and urea also form true

solutions in water .

solutions colloids suspensions

<1 nm >100 nm

-single atoms-small molecules-ions-polyatomic ions

-aggregates of atoms, molecules or

ions-macromolecules

(proteins)

-clumps of particles,

-mineral grains such as sand

Comparison of Solutions, Colloids, and Suspensions

http://academic.pgcc.edu/~ssinex/Solutions.ppt

Suspensions• Suspensions consist of particles of a solid suspended in

a liquid medium. Suspensions are systems with two distinct phases. The particles in suspensions are bigger than 100 nm to 200 nm across. The particles of a suspension may not be visible to the naked eye but are visible under a microscope. Suspensions are heterogeneous systems. They stay only for a limited period i.e. these are not stable as the particles have a tendency to settle down under the influence of gravity. The particles of a suspension can neither pass through ordinary filter paper nor through animal membranes.

• Examples of suspensions are sodium chloride in benzene, turmeric in water, silver chloride, barium sulphate or sand in water.

Colloidal solution or colloidal state or colloidal dispersion

They represent an intermediate kind of a mixture between true solution and suspension. The size of a colloidal particle lies roughly between 1-100 nm. Colloids are also a two-phase heterogeneous system consisting of

the dispersed phase and dispersion medium .

Colloidal solution or colloidal state or colloidal dispersion

Since the dispersed phase in a colloidal system is uniformly distributed in the dispersion medium, the colloidal state appears homogenous to the naked eye or even an ordinary microscope (due to particles being invisible). However it is a heterogeneous dispersion of two immiscible phases and this is proved by viewing it under an ultra-microscope, where the light reflected by colloidal particles can be seen. Colloidal particles do not settle down under gravity: a colloidal solution of gold prepared by Faraday over 125 years ago continues to be in excellent condition even today. Colloids can pass through ordinary filter paper but do not

pass through animal membranes.•  

Difference Between True Solutions, Suspensions and Colloidal Solutions

solutions colloids suspensions

<1 nm >100 nm

transparent with Tyndall effect

translucent)cloudy(

molecular motion Brownian motion- colloidal particles moved by solvent

movement by gravity

coagulation – can settle

never settle

transparent)clear(

http://academic.pgcc.edu/~ssinex/Solutions.ppt

Classification of Colloids Based on Type of Phases

Each of the two phases of a heterogeneous colloidal system i.e., the dispersed phase and dispersion medium, can be in any one of the three physical states of matter. We have eight different types of colloidal solutions (not nine), since a colloidal state of gas-in-gas forms a single phase (gases consist of molecules, and with molecules of both gases mixing in all proportions, two separate phases do not form).

solutions colloids suspensions

-dissolved in water electrolytes

(salts) gases glucose

-plasma proteins albumins globulins fibrinogen

-cellular stuff red blood cells white blood cells platelets

Using whole blood as an example…

http://academic.pgcc.edu/~ssinex/Solutions.ppt

Types of Colloidal Solutions

Properties of Colloids

1. Heterogeneity

A colloidal solution is heterogeneous system consisting of two phases of dispersed phase (colloidal particles of a solid) and the aqueous dispersion medium. Often a colloidal sol appears to be homogeneous as the particles are small in size and not visible to the naked eye. However, this is disproved when it is viewed under electron microscope.

Properties of Colloids

2-Stable nature

Colloidal solutions are quite stable. The colloidal particles do not settle at the bottom under the influence of gravity. This is because of the constant motion of colloidal particles.

3-Filterability

Colloidal particles do not pass through ultrafilter papers, animal and vegetable membranes. The large pore size of ordinary filter paper enables colloidal particles to pass through.

Colligative properties

In colloidal systems the number of colloidal particles per liter of the sol is relatively much smaller than solute particles in a true solution. Colloidal particles are aggregates of simple molecules and colligative properties such elevation in boiling point, depression in freezing point and lowering of vapour pressure depend upon the number of colloid particles present in system and not on the nature of the particle. The values of colligative properties are consequently

much smaller as compared to true solutions .

Mechanical Properties (Brownian movement)

• When colloidal solutions have been observed through ultra microscope, the colloidal particles are seen in constant and rapid zigzag motion called Brownian movement. Sir Robert Brown first observed the phenomenon in 1827. Suspensions and true solutions do not exhibit Brownian movement.

Optical Properties (Tyndall Effect)

When a strong beam of light is passed through a colloidal solution, the path of the light becomes visible when viewed from a direction at right angle to that of the incident light. This occurs because the colloidal particles absorb light energy and then scatter it in all directions. The phenomenon of scattering of light by sol particles to form illuminated beam or cone is called Tyndall effect or Tyndall beam or Tyndall cone.

solutions colloids suspensions

<1 nm >100 nm

http://academic.pgcc.edu/~ssinex/Solutions.ppt

Passage of light Scattering in beam Scattering inall directions

Absorption of light

Electrical Properties (Electrophoresis)

Colloidal particles of a sol either carry positive or negative charge. Sols in, which the colloidal particles carry positive charge are called positive sols. When colloidal particles carry negative charge, the sols are called negative sols. The existence of charge on the colloidal particles can be demonstrated by a phenomenon called electrophoresis where the colloidal particles, when placed in an electric field, move towards either cathode or anode depending upon the charge on them. Sols of basic dyestuffs, ferric hydroxide, aluminium hydroxide etc., are some common examples of positive sols. Colloidal solutions of gums, starch, soap solution, metals (Ag, Cu, Au, Pt etc.), metal sulphides, and some acid dyestuffs are the examples of negative sols

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