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Which method of concentration of ore is ...

Which method of concentration of ore is preferred in the following cases and why ?
(i) The ore has higher density particles mixed with a large bulk of low density impurities.
(ii) The ore consists of copper sulphide intermixed with clay particles. Give an example of amalgam.

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(i) The concentration of ore can be done by Gravity Separation method.
(ii) The concentration of ore is done by Froth Floatation process.
An amalgam of mercury with silver or gold called dental alloy is used to fill cavities in the teeth.
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The method of concentrating the ore which makes use of the difference in density between ore and impurities is called

A tapping vessel opens in a tank like container that is tapering on the lower side. The tank has an outlet for water on the upper side and a water inlet on the lower side. Finely ground ore is released in the tank. A forceful jet of water is introduced in the tank from lower side and gangue particles and pure ore are separated by this method. i. The above description is of which gravitation separation method? ii. Draw labelled diagram of this method.

Give reasons for the following : (i) Zinc can displace copper from copper sulphate solution. (ii) Silver articles become black after sometime when exposed to air. (iii) A metal sulphide is converted to its oxide to extract the metal from sulphide ore.

Read the passage given below and answer the following questions: 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 (source: Sarquis, J. (1980). Colloidal systems. Journal of Chemical Education, 57(8), 602. doi:10.1021/ed057p602 ) Settling down of colloidal particles to form a suspension is called:

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