effloresence

Question 1

effloresence intro

Answer 1

is the loss of water of crystallaization from a hydrated salt to the atmosphere on exposure to air
-the loss of water of crystallization by hydrated crystalline substance with water of crystallization to fom anhydrons salts or hydrate with less molecules of water of crystallization is called effloresence

Question 2

hydrates

Answer 2

-Solids that contain water mdlecules as part of their crystalline structure.
-The water in the hydrate is known as the water of hydration or the water of crystallization.
-A large number of compounds crystallize in hydrated form. e.g.,
CuSO4 combines with 5 molecules of water
Na2SO4 combines with 10 molecules of water
-Presence of water of crystallization is not essential for crystal structure, as Sodium chloride, potassium nitrate and many other compounds have definite crystal structures without water of crystallization.

Question 3

principle

Answer 3

-if the vapor pressure of a hydrated salt is greater than the pressure exerted by the water vapors in the surrounding atmosphere then the salt tempt to attain equilibrium with its surroundings and will therefore tend to lose its water to form a lower hydrate or an anhydrous salt
-This phenomenon is called as Efferescence. —–For example, the vapor pressure of washing soda (Na:CO.10H:O) normally exceeds that of the water vapor in the atmosphere, these salts effloresce (ie., lose all or part of their water of hydration). and their surfaces assume a powdery appearance.
-A salt such as copper sulfate may form more than one hydrate, each of which possesses its own definite vapor pressure at a given temperature. The following hydrates of copper sulfate are known:
CuSOSH:O, CuSO3H:O and CuSOLH:0
-When certain substances of low vapor pressure, such as CaCl. HO, are exposed to air, they form higher hydrates. Such salts may be used in the removal of moisture from air or other gases.

Question 4

example

Answer 4

-Pressure of water vapor in the atmosphere is about 13.3X10 N/m2 at 293 k.
-Therefore, the hydrates with vapor pressure greater than this will show efflorescence and will be unstable, provided that the lower hydrate formed still exert a vapor pressure greater than the surrounding atmosphere.
-If this is not so, the water will be taken up from the atmosphere by the lower hydrate as fast as it is formed and the final equilibrium will depend on the rates at which water is lost or taken up by the
two hydrates.
E.g.
o The behavior of various forms of sodium carbonate.
。 Sodium Sulphate
o Certain salts of quinine
-the vapor pressure exerted by the dehydrate is much greater than that of normal atmosphere and it loses water by efflorescence and is converted to monohydrate
-the vapor pressue of it is stil above that of atmosphere, but further apparent loss of water does not occur because the anhydrous salt is rehydrated at a faster rate than dehydration of the monohydrate.
-the vapor pressure of hydrated salts, and therefore the rate of effloresence increases with rise in temp

Question 5

application

Answer 5

-hydrated drug on weight basis is less potent but when it is converted by efflorescne to its correspoding lower hydrates, or anhydrous form then its potency can be increases
-anhydrous form is easy to handle during manufacturing process

Question 6

precutaion

Answer 6

-the container that prevents the loss of water vapors should be used to avoid instability
-store in a cool place because greater is the temperatue greater is the release of water of crystallization