Advertisements
Advertisements
प्रश्न
Comment on the statement that “colloid is not a substance but a state of substance”.
Advertisements
उत्तर
Common salt (a typical crystalloid in an aqueous medium) behaves as a colloid in a benzene medium. Hence, we can say that a colloidal substance does not represent a separate class of substances. When the size of the solute particle lies between 1 nm and 1000 nm, it behaves as a colloid.
Hence, we can say that a colloid is not a substance but a state of the substance, which is dependent on the size of the particle. A colloidal state is intermediate between a true solution and a suspension.
संबंधित प्रश्न
Identify the dispersed phase and dispersion medium in the following colloidal dispersions.
- milk
- blood
- printing ink
- fog
Write a note on the Tyndall effect.
Draw labelled diagram of Soap micelle.
Froth and whipped cream are examples of ____________.
Which of the following is multimolecular colloid?
Which of the following is a heterogeneous mixture?
Which of the following statements is CORRECT?
Mixing of two oppositely charged sols leads to ____________.
Froth is a colloidal solution of ____________.
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.
Gelatin is a _________ colloidal system.
Which of the following electrolytes will have maximum coagulating value for AgI/Ag+ solution?
A colloidal system having a solid substance as a dispersed phase and a liquid as a dispersion medium is classified as ______.
What is collodion?
Why are some medicines more effective in the colloidal form?
How does the precipitation of colloidal smoke take place in Cottrell precipitator?
Colloids can
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?
Identify the correct decreasing order of precipitation power of flocculating ion added, from following.
