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प्रश्न
Explain the term emulsion and types of emulsions.
उत्तर
- A colloidal system in which one liquid is dispersed in another immiscible liquid is called an emulsion.
- There are liquid-liquid colloidal systems in which both liquids are either completely or partially immiscible.
- There are two types of emulsions:
- Emulsion of oil in water (o/w type):
An emulsion in which a dispersed phase is oil and the dispersion medium is water is called emulsion of oil in water.
Example:
1. Milk consists of particles of fat dispersed in water.
2. Other examples include vanishing cream, paint, etc. - Emulsion of water in oil (w/o type):
An emulsion in which the dispersed phase is water and dispersion medium is the oil is called emulsion of water in oil.
Example:
1. Cod liver oil consists of particles of water dispersed in oil.
2. Some other examples of this type include butter, cream, etc.
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संबंधित प्रश्न
Choose the correct option.
The size of colloidal particles lies between ______.
Define the term Electrophoresis.
Identify the dispersed phase and dispersion medium in the following colloidal dispersions.
- milk
- blood
- printing ink
- fog
Write Hardy-Sulze rules.
Write a note on Brownian motion.
Explain micelle formation in a soap solution.
Draw labelled diagram of Bredig’s arc method.
Draw labelled diagram of Soap micelle.
Froth and whipped cream are examples of ____________.
In coagulation of positively charged ferric hydroxide sol, the most and least effective ions are ____________ and ____________ respectively.
Which of the following is an example of liquid-liquid system?
The movement of colloidal particles towards respective electrode under electric field is called ______.
Some colloids are stable by their nature, i.e., gels, alloys, and solid foams. Gelatin and jellies are two common examples of a gel. The solid and liquid phases in a gel are interdispersed with both phases being continuous. In most systems, the major factor influencing the stability is the charge on the colloidal particles. If a particular ion is preferentially adsorbed on the surface of the particles, the particles in suspension will repel each other, thereby preventing the formation of aggregates that are larger than colloidal dimensions. The ion can be either positive or negative depending on the particular colloidal system, i.e., air bubbles accumulate negative ions, sulphur particles have a net negative charge in a sulphur sol, and the particles in a metal hydroxide sol are positively charged. Accumulation of charge on a surface is not an unusual phenomenon-dust is attracted to furniture surfaces by electrostatic forces. When salts are added to lyophobic colloidal systems the colloidal particles begin to form larger aggregates and a sediment forms as they settle. This phenomenon is called flocculation, and the suspension can be referred to as flocculated, or colloidally unstable. If the salt is removed, the suspension can usually be restored to its original state; this process is called deflocculation or peptization. The original and restored colloidal systems are called deflocculated, peptized, or stable sols.
Why does a small amount of salt have such a dramatic effect on the stability of a lyophobic colloidal system? The answer lies in an understanding of the attractive and repulsive forces that exist between colloidal particles. Van der Waals forces are responsible for the attractions, while the repulsive forces are due to the surface charge on the particles. In a stable colloid, the repulsive forces are of greater magnitude than the attractive forces. The magnitude of the electrical repulsion is diminished by addition of ionized salt, which allows the dispersed particles to aggregate and flocculate. River deltas provide an example of this behaviour. A delta is formed at the mouth of a river because the colloidal clay particles are flocculated when the freshwater mixes with the salt water of the ocean.
Gelatin is a _________ colloidal system.
Some colloids are stable by their nature, i.e., gels, alloys, and solid foams. Gelatin and jellies are two common examples of a gel. The solid and liquid phases in a gel are interdispersed with both phases being continuous. In most systems, the major factor influencing the stability is the charge on the colloidal particles. If a particular ion is preferentially adsorbed on the surface of the particles, the particles in suspension will repel each other, thereby preventing the formation of aggregates that are larger than colloidal dimensions. The ion can be either positive or negative depending on the particular colloidal system, i.e., air bubbles accumulate negative ions, sulphur particles have a net negative charge in a sulphur sol, and the particles in a metal hydroxide sol are positively charged. Accumulation of charge on a surface is not an unusual phenomenon-dust is attracted to furniture surfaces by electrostatic forces. When salts are added to lyophobic colloidal systems the colloidal particles begin to form larger aggregates and a sediment forms as they settle. This phenomenon is called flocculation, and the suspension can be referred to as flocculated, or colloidally unstable. If the salt is removed, the suspension can usually be restored to its original state; this process is called deflocculation or peptization. The original and restored colloidal systems are called deflocculated, peptized, or stable sols.
Why does a small amount of salt have such a dramatic effect on the stability of a lyophobic colloidal system? The answer lies in an understanding of the attractive and repulsive forces that exist between colloidal particles. Van der Waals forces are responsible for the attractions, while the repulsive forces are due to the surface charge on the particles. In a stable colloid, the repulsive forces are of greater magnitude than the attractive forces. The magnitude of the electrical repulsion is diminished by addition of ionized salt, which allows the dispersed particles to aggregate and flocculate. River deltas provide an example of this behaviour. A delta is formed at the mouth of a river because the colloidal clay particles are flocculated when the freshwater mixes with the salt water of the ocean.
Settling down of colloidal particles to form a suspension is called ______.
A colloidal system having a solid substance as a dispersed phase and a liquid as a dispersion medium is classified as ______.
An emulsion cannot be broken by:
(i) heating
(ii) adding more amount of dispersion medium
(iii) freezing
(iv) adding emulsifying agent
Which of the following substances will precipitate the negatively charged emulsions?
(i) \[\ce{KCl}\]
(ii) glucose
(iii) urea
(iv) \[\ce{NaCl}\]
What happens when electric field is applied to colloidal solution?
Why are some medicines more effective in the colloidal form?
How does the precipitation of colloidal smoke take place in Cottrell precipitator?
For coagulating 200 ml of arsenious sulphide sol, 10 ml of 1 m NaCl solution is required find out the flocculation value of NaCl.
The size of a raw mango shrinks to a much smaller size when kept in a concentrated salt solution. Which one of the following processes can explain this?
The migration of dispersion medium under the influence of an electric potential is called ______.
Which of the following is most powerful to coagulate the negative colloid?
Smoke is an example of ______.
Blood may be purified by ______.
Van Arkel's method of purification of metals involves converting the metal to a ______.
Identify positively charged sol from following.
Identify the correct decreasing order of precipitation power of flocculating ion added, from following.
