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प्रश्न
Write a note on the Tyndall effect.
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उत्तर
- Tyndall observed that when light passes through a true solution, the path of light through it cannot be detected.
- However, if the light passes through a colloidal dispersion, the particles scatter some light in all directions and the path of the light through colloidal dispersion becomes visible to an observer standing at right angles to its path.
- The phenomenon of scattering of light by colloidal particles and making the path of light visible through the dispersion is referred to as the Tyndall effect and the bright cone of the light is called the Tyndall cone.
- The Tyndall effect is observed only when the following conditions are satisfied.
a. The diameter of the dispersed particles is not much smaller than the wavelength of light used.
b. The refractive indices of the dispersed phase and dispersion medium differ largely. - Significance of Tyndall effect:
a. It is useful in determining the number of particles in the colloidal system and their particle size.
b. It is used to distinguish between colloidal dispersion and true solution.
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संबंधित प्रश्न
Comment on the statement that “colloid is not a substance but a state of substance”.
Write Hardy-Sulze rules.
Draw labelled diagram Tyndall effect.
Draw labelled diagram Dialysis.
Identify the CORRECT statement.
Identify the CORRECT statements from the following.
i. The colour of colloidal dispersion depends on size of colloidal particles.
ii. Tyndall effect is used to distinguish between colloidal dispersion and true solution.
iii. Eosin and congo red are examples of negatively charged sols.
In coagulation of positively charged ferric hydroxide sol, the most and least effective ions are ____________ and ____________ respectively.
Which of the following is a heterogeneous mixture?
Which of the following is an example of liquid-liquid system?
Tyndall effect is observed due to ____________.
Smoke is an example of ____________.
Which of the following can form colloidal sol with water?
Tyndall effect is useful ______.
Pumice stone is an example of ______.
Which of the following ionic species has highest precipitating power?
In which of the following sols there is low affinity between dispersed phase and dispersion medium?
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.
Colloidal solutions are stable due to ______.
Freshly prepared precipitate sometimes gets converted to colloidal solution by ______.
Which of the following substances will precipitate the negatively charged emulsions?
(i) \[\ce{KCl}\]
(ii) glucose
(iii) urea
(iv) \[\ce{NaCl}\]
A colloid is formed by adding \[\ce{FeCl3}\] in excess of hot water. What will happen if excess sodium chloride is added to this colloid?
Why are some medicines more effective in the colloidal form?
Why is \[\ce{Fe(OH)3}\] colloid positively charged, when prepared by adding \[\ce{FeCl3}\] to hot water?
Toluene is oxidised to benzoic acid by
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?
In which of the following, the Tyndall effect is not observed?
Smoke is an example of ______.
