Question

40. The post precipitation can be avoided by
Using water immiscible liquid
Using water miscible liquid
O Digestion for longer time
Delaying the filtration​

Answer 1

Answer:

Gravimetric analysis, which by definition is based upon the measurement of mass, can be generalized into two types; precipitation and volatilization. The quantitative determination of a substance by the precipitation method of gravimetric analysis involves isolation of an ion in solution by a precipitation reaction, filtering, washing the precipitate free of contaminants, conversion of the precipitate to a product of known composition, and finally weighing the precipitate and determining its mass by difference. From the mass and known composition of the precipitate, the amount of the original ion can be determined.

For successful determinations the following criteria must be met: The desired substance must be completely precipitated. In most determinations the precipitate is of such low solubility that losses from dissolution are negligible. An additional factor is the "common ion" effect, this further reduces the solubility of the precipitate. When Cl- is precipitated out by addition of Ag+

Ag+ + Cl- AgCl(s)

The (low) solubility of AgCl is reduced still further by the excess of Ag+ which is added, pushing the equilibrium to the right. We can further decrease the solubility by decreasing the temperature of the solution by using an ice bath. The weighed form of the product should be of known composition. The product should be "pure" and easily filtered. It is usually difficult to obtain a product which is "pure", i.e. one which is free from impurities but careful precipitation and sufficient washing helps reduce the level of impurity.

Explanation:

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Answer 2

The post precipitation can be avoided by using water-immiscible liquid.

Explanation:

• Post precipitation is the kind of precipitation where the precipitation of the undesirable compound takes place after the formation of the precipitate of the desired compound.
• In post precipitation degree of contamination is low.
• It is the precipitation where it transpires as a layer upon the already formed precipitate.
• Post precipitation occurs when the solution is in supersaturated form and here a foreign substance gets precipitated very slowly.
• It can be prevented by filtering the ppt.
• Post precipitation is the precipitation of a second solution, which is often related to the substance upon the surface of an initial precipitate.