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Questions
Write Hardy-Sulze rules.
Write a note on Hardy–Schulze rule.
Solution
- Generally, the greater the valency of the flocculating ion added, the greater is its power to cause precipitation. This is known as the Hardy–Schulze rule.
- In the coagulation of negative sol, the flocculating power follows the following order:
Al3+ > Ba2+ > Na+ - Similarly, in the coagulation of positive sol, the flocculating power is in the following order:
\[\ce{[Fe(CN)_6]^{4-} > PO_4^{3-} > SO_4^{2-} > Cl^-}\]
RELATED QUESTIONS
Define the following with a suitable example, of each:
Multimolecular colloid
Choose the correct option.
The size of colloidal particles lies between ______.
Write a note on the Tyndall effect.
Write a note on Types of emulsion.
What happens when a beam of light is passed through a colloidal sol.
Explain the term emulsion and types of emulsions.
Draw labelled diagram of Bredig’s arc method.
Which type of colloid is formed on the dissolution of soap in water?
Froth and whipped cream are examples of ____________.
Which of the following is multimolecular colloid?
Mist is a colloidal solution of ____________.
The precipitation power of an electrolyte increases with ______.
The order of coagulating power of following ions in the coagulation of a positive sol is:
i. \[\ce{PO^{3-}_4}\]
ii. \[\ce{SO^{2-}_4}\]
iii. \[\ce{[Fe(CN)6]^{4-}}\]
iv. \[\ce{NO^-_3}\]
Smoke is an example of ____________.
Which of the following compounds forms a colloidal solution when dissolved in water?
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.
A colloidal system having a solid substance as a dispersed phase and a liquid as a dispersion medium is classified as ______.
What happens when electric field is applied to colloidal solution?
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?
How do emulsifying agents stabilise the emulsion?
Toluene is oxidised to benzoic acid by
Which of the following substances will precipitate the negatively charge emulsion
The migration of dispersion medium under the influence of an electric potential is called ______.
In which of the following, the Tyndall effect is not observed?
Smoke is an example of ______.
Identify the colloidal molecule containing hydrophilic head and hydrophobic tail within it.
Identify positively charged sol from following.
