--%>
Assignment Help - homework help

What are emulsions?Describe its preparation and tests.

Emulsions are colloidal solutions in which disperse phase as well as dispersion medium is both liquids. Emulsions can be broadly classified into two types:


(i) Oil in water (O/W type) emulsions: in this type of emulsions, oil acts disperse phase and water acts as dispersion medium. Some examples of this type of emulsions are milk, vanishing cream, etc.

(ii) Water in oil (W/O type) emulsions: in this type of emulsions, water acts as disperse phase and oil acts as dispersion medium. Some examples are cold cream, butter, cod liver oil etc.

The two types of emulsions can be interconverted simply by changing the proportion of the dispersed phase and dispersion medium. For example, O/W type of emulsion can be converted W/O type by adding excess of oil to O/W emulsion.

Detection of emulsions

The below mentioned tests may be applied to distinguish between the two types of emulsions:

(i) Dye test: to the emulsion some oil soluble dye is added. If the background becomes coloured, the emulsion is water in oil type and if the droplets become coloured, the emulsion is oil in water type.

(ii) Dilution test: if the emulsion can be diluted with water, this indicates that water act as the dispersion medium and the emulsion is of oil in water type. If the added water forms a separate layer, then in that case the emulsion is water-in-oil type.

Preparation of emulsions

The process of making an emulsion known as emulsification. Emulsions may be obtained by vigorously agitating a mixture of both the liquids. But this gives an unstable emulsion the dispersed drops at once come together and form a separate layer. To stabilize an emulsion, the addition of a small quantity of the third substance known as emulsify agent or emulsifier is essential. The emulsified agents form an interfacial film between suspended particles and the dispersion medium. For example, soaps and detergents are frequently used as emulsifiers. They coat the drops of an emulsion and check them from coming together thereby establishing the emulsion. The principle emulsifying agent for W/O type emulsions are heavy metal salts of fatty acids, long chain alcohols, lamp black, etc. the emulsifying agents used for O/W type emulsions are proteins, gums, natural and synthetic soaps, etc.

   Related Questions in Chemistry

  • Q : Relationship between free energy and

    The free energy of a gas depends on the pressure that confines the gas. The standard free energies of formation, like those allow predictions to be made of the possibility of a reaction at 25°C for each reagent at 

    		•
  • Q : F-centres If a electron is present in

    If a electron is present in place of anion in a crystal lattice, then it is termed as: (a) Frenkel defect  (b) Schottky defect  (c) Interstitial defects (d) F-centre Answer: (d) When electrons are trapped in anion vacancies, thes

    		•
  • Q : Coagulation what is the meaning of

    what is the meaning of fourth power of valency of an active ion?

    		•
  • Q : Partial vapour pressure of volatile

    Choose the right answer from following. For a solution of volatile liquids the partial vapour pressure of each component in solution is directly proportional to: (a) Molarity (b) Mole fraction (c) Molality (d) Normality

    		•
  • Q : Basicity order order of decreasing

    order of decreasing basicity of urea and its substituents

    		•
  • Q : Carnot cycle show how a mathematical

    show how a mathematical definition of entropy can be obtauined from a consideration of carnot cycle?

    		•
  • Q : Problem on mole fraction of glucose

    Provide solution of this question. While 1.80gm glucose dissolve in 90 of H2O , the mole fraction of glucose is: (a) 0.00399 (b) 0.00199 (c) 0.0199 (d) 0.998

    		•
  • Q : Question of vapour pressure Choose the

    Choose the right answer from following. Vapour pressure of a solution is: (a) Directly proportional to the mole fraction of the solvent (b) Inversely proportional to the mole fraction of the solute (c) Inversely proportional to the mole fraction of the solvent (d

    		•
  • Q : Linde liquefaction process Liquefied

    Liquefied natural gas (LNG) is produced using a Linde liquefaction process from pure methane gas at 3 bar and 280 K (conditions at point 1 in figure below). A three-stage compressor with interceding is used to compress the methane to 100 bar (point 2). The first stage

    		•
  • Q : Infrared Adsorption The adsorption of

    The adsorption of infrared radiation by diatomic molecules increases the vibrational energy fo molecules and gives information about the force constant for the "spring" of the molecule.;The molecular motion that has the next larger energy level spacing aft

    		•