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Sorption (from Lat.o A sorbate or sorptive is an absorbed substance

Sorption is the process in which one substance takes up or holds another (adsorption or absorption)

A sorbate or sorptive is the absorbed substance

A sorbent is any agent that absorbs or adsorbs (absorber).Liquid/liquid: in this case molecules of surface active compounds, that were initially dissolved in one or both liquids, are adsorbed on the frontier of two liquids, which are insoluble in each other (water-benzine)

Solid/gas: in this case the gas molecules are adsorbed on the surface of a solid substance.This adsorption involves the formation of chemical linkages adsorbed molecules and the surface of adsorbent Molar heat is high.In other words, the phenomenon of attracting and retaining the molecules of a substance of a liquid or solid resulting into higher concentration of the molecules on the surface is called adsorption.sorbeo - absorb) is the process of absorption of one substance

(gas, liquid or dissolved component) by the surface or volume of another.The surfaces on which adsorption occurs can be divided into two groups: mobile and fixed.Liquid/gas: In this case in frontier between liquid and gas there adsorbed molecules of the so-called surface active compounds, that are dissolved in the liquid.This adsorption first increases with increase in temperature up to a certain extant and decreases regularly.If temperature is increased, the kinetic energy of the gas molecules increases and they leave the surface of the adsorbent.Adsorption on the liquid frontie

A compound can adsorbed on the surface of liquid, if the presence of this compound in the surface of liquid decreases the surface free energy.o Process of sorption of one substance by the volume is called absorption.o A sorbent is a substance (absorber) that absorbs another.Absorption is a process in which one substance binds another in its volume.The process of removal of an adsorbed substance from the surface on which it is adsorbed is called desorption.There aren't physical forces between adsorbent and adsorbate.In physical adsorption, the state of adsorbate is same as in the bulk.Adsorption can occur at the surface of both solid and liquid substances.Solid/liquid: In this case the solute molecules from the liquid phase are adsorbed on the surface of a solid substance.Such compound is called Surface active compound (SAC).o Process of sorption of one substance by the surface is called adsorption.As a result of adsorption, there is decrease of surface energy.The substance on the surface of which adsorption takes place is called adsorbent.The substance adsorbed is a adsorbate.There are chemical forces between adsorbent and adsorbate.The equilibrium is reached rapidly.Absorption.Adsorption is a process in which one substance becomes bound to the surface of another.Chemical adsorption.This attractive forces are strong chemical bonds.It is irreversible process.Physical adsorption.This attractive forces are weak chemical bonds.It is reversible process.Molar heat is low.Most often it is a solid

substance.

Sorption (from Lat. sorbeo - absorb) is the process of absorption of one substance

(gas, liquid or dissolved component) by the surface or volume of another.

• Process of sorption of one substance by the volume is called absorption.

• Process of sorption of one substance by the surface is called adsorption.

• A sorbent is a substance (absorber) that absorbs another. Most often it is a solid

substance.

• A sorbate or sorptive is an absorbed substance

Sorption is the process in which one substance takes up or holds another (adsorption or absorption)

A sorbate or sorptive is the absorbed substance

A sorbent is any agent that absorbs or adsorbs (absorber). Absorption.

Absorption is a process in which one substance binds another in its volume.

Adsorption is a process in which one substance becomes bound to the surface of another.

In other words, the phenomenon of attracting and retaining the molecules of a substance of a liquid or solid resulting into higher concentration of the molecules on the surface is called adsorption. As a result of adsorption, there is decrease of surface energy. The substance on the surface of which adsorption takes place is called adsorbent. The substance adsorbed is a adsorbate. The process of removal of an adsorbed substance from the surface on which it is adsorbed is called desorption.

Chemical adsorption. There are chemical forces between adsorbent and adsorbate. This attractive forces are strong chemical bonds. It is irreversible process. This adsorption first increases with increase in temperature up to a certain extant and decreases regularly. This adsorption involves the formation of chemical linkages adsorbed molecules and the surface of adsorbent Molar heat is high.

Physical adsorption. There aren't physical forces between adsorbent and adsorbate. This attractive forces are weak chemical bonds. It is reversible process. The equilibrium is reached rapidly. If temperature is increased, the kinetic energy of the gas molecules increases and they leave the surface of the adsorbent. In physical adsorption, the state of adsorbate is same as in the bulk. Molar heat is low.

Adsorption can occur at the surface of both solid and liquid substances.

The surfaces on which adsorption occurs can be divided into two groups: mobile and fixed.

Liquid/gas: In this case in frontier between liquid and gas there adsorbed molecules of the so-called surface active compounds, that are dissolved in the liquid.

Liquid/liquid: in this case molecules of surface active compounds, that were initially dissolved in one or both liquids, are adsorbed on the frontier of two liquids, which are insoluble in each other (water-benzine)

Solid/gas: in this case the gas molecules are adsorbed on the surface of a solid substance. Solid/liquid: In this case the solute molecules from the liquid phase are adsorbed on the surface of a solid substance.

Adsorption on the liquid frontie

A compound can adsorbed on the surface of liquid, if the presence of this compound in the surface of liquid decreases the surface free energy. Such compound is called Surface active compound (SAC). Molecule of the surface active compound has biophilic structure ("head" and "tail"). The non-polar part

is indicated by the tail, the polar part is indicated by the head.

Compounds, that are adsorbed at surfaces of liquids and cause a decrease of the surface free energy (surface tension) of liquid, are called surface active compounds (SAC) The surface activity, g, is found as:

da

9=-=- AC

and it is defined as the change of surface tension of the solution, caused by an increase of SAC concentration for 1 mole/I. Dissolved substances depending on their nature can influence the surface tension of liquids in different ways. The ability of dissolved substances to change the surface tension of a solvent is called surface activity. According tothe ability to change the surface tension all the substances are divided into three groups:

1. 
   

   Surface-active substances (SAS) which reduce the surface tension of a solvent. With respect to water SAS are a number of organic substances: alco- hols, acids of aliphatic series and their salts (soaps), esters, amines, proteins and so on.

   
   


2. 
   

   Surface-inactive substances (SIS) which increase insignificantly the surface tension of a solvent. With respect to water SIS are a number of inorganic acids, bases, salts and some organic substances like glycine (aminoacetic acid).

   
   


3. 
   

   Surface-non-active substances (SNS) which don't change the surface tension at all. With respect to water SNS is saccharose and some other substanc-es.

   
   

In some cases the biologi-cal activity (e.g. narcotic action, bactericidal action

and so on) of the substances of the same ho-mologous series increases with the increase of their surface ac-tivity. Ducklo-Traube rule is ob-served only for aqueous solutions of SAS. The ability of SAS to de-crease water surface tension can be explained by the fact that SAS molecules consist of non-polar hydrocarbon part and the polar one represented by the following functional groups -COOH; OH, -NH2 and oth- ers. Such substances are called diphilic. Diphilic SAS molecules are denoted by symbol where a circle is a polar group and a dash is a non-polar radical.

COMPARISON OF THE SURFACE ACTIVITY OF DIFFERENT SAC. TRAUBE'S RULE.

The surface activity increases with the increase of the length of hydrocarbon radical in the molecule of SAC. For univalent organic acids an increase of the length of hydrocarbon radical by one -CH2-group causes an increase of surface activity 3-5 times.

The adsorption of SAC at the boundary between liquid and gas is described by the Gibbs equation.

As can you see from Gibbs's equation depends on the following factors:

a) Concentration of SAC-the greater it is, the greater is adsorption;

b) temperature the greater it is, the smaller becomes adsorption;

c) surface activity of solute (-d6/dC) - the greater it is, the greater is adsorption

Adsorption isotherm is a curve, that shows the dependence of adsorption on the concentration of SAC at a given temperature.

This slide shows that the adsorption isotherm has 3 areas.

Area I: While concentration of SAC is very small, all the surface of liquid is free and molecules of SAC immediately finds a free place in the surface, therefore adsorption is proportional to concentration C.

Area II: When the concentration of active substance grows biggerthe adsorption value is described by the Langmuir equation

Area III: At very great concentrations of active compounds, The maximal adsorption is already reached.

Adsorption value on the solid/gas frontier.

The reason for adsorption of gases on solid surfaces is the existence of Van der Vaal's forces

THE VALUE OF ADSORPTION IS DETERMINED BY:

1. 
   

   the specific surface of adsorbent - the greater it is, the greater is adsorption. For this reason the adsorbent has to be ground to a small particle size.

   
   


2. 
   

   temperature - the greater it is, the more intensive is the thermal motion of gas molecules and the smaller becomes adsorption.

   
   


3. 
   

   pressure (concentration) of gas - the greater it is, the greater is adsorption.

   
   


4. 
   

   nature of gas and adsorbent (solid) - polar adsorbents (for instance, silica gel SiO2) better adsorb polar gases, non-polar adsorbents better adsorb molecules of non-polar gases.

   
   


5. 
   

   when adsorption of different gases on the same solid adsorbent is compared, it is found out, that adsorption is greater for the gases, that can be liquefied more easily.

   
   

The theory of Langmuir

1. 
   

   The surface of a solid adsorbent contains active centers that are distributed over its entire surface.

   
   


2. 
   

   The active center can only adsorb one gas molecule, i.e. the adsorption is monomolecular

   
   


3. 
   

   The adsorption is characterized by a dynamic equilibrium of adsorption = desorption.

   
   


4. 
   

   When all active centers are filled, the adsorption value reaches its maximum possible value roo

   
   

The Langmuir adsorption isotherm at the solid-gas interface has the form

Area I: while the concentration is small, causes a proportional increase in adsorption.

Area II:Adsorption grows less then proportionally to the concentration (pressure)

of adsorbate.

Area III: all the surface of adsorbent is already covered by the molecules of adsorbate, no more molecules can be adsorbed at an increase of concentration

(pressure) of adsorbate. A maximal adsorption value is reached

Where I is the value of adsorption [mol/g) roo is the maximal adsorption [mole/g] P is pressure of gas C is concentration of solute K is Langmuir's constant. It is equal to the ratio between the rate adsorption constant and desorption constant, K=kads/kdes

I: If the concentration (pressure) of adsorbate is low and Kc