The salt which is efflorescent and the residue after exposure is an anhydrate.
A: Washing soda
B: Calcium chloride
C: Glauber's salt
D: Iron [III] chloride
The salt whose solubility in water decreases with rise in temperature.
A: Calcium sulphate
B: Sodium nitrate
C: Potassium nitrate D: Ammonium chloride
(iii)
The anhydrous salt which changes colour on reaction with water.
A: Calcium sulphate B: Sodium sulphate
C: Cobalt chloride
D: Calcium chloride
Answers
The salt that show effloroscence is : washing soda .
The salt whose solubility in water decreases with rise in temperature is :Calcium sulphate
Explanation:
Washing soda is chemically : Sodium carbonate decahydrate that is Na₂CO₃.10H₂O
This shows a property of effloroscence that is : Loss of 9 molecules of water of crystallization when exposed to air .
The reaction for the same is given below :
Na₂CO₃.10H₂O ---------------------> Na₂CO₃.H₂O + 9H₂O
(on exposure to air )
The solubility of calcium sulphate decreases in water with rise in temperature because :
When the temperature of the system is increased, the equilibrium will shift towards the left according to Le Chatelier principle and as a result the solubility of calcium sulfate decreases, when temperature increases.
Washing soda, Calcium sulphate, and Copper(II)sulphate
Explanation:
(i) Washing soda and Glauber's salt
Efflorescence is a process of loss of water by a hydrated salt, which occurs when the vapour pressure of the hydrate is more than the partial pressure of the water vapour in the air.
The vapour pressures of washing soda and Glauber’s salt is more than that of the water vapour in the atmosphere, these salts lose all or part of their water of hydration and their surfaces leave behind a powdery appearance.
(ii) Calcium sulphate
Calcium sulphate (anhydrous) doesn't give a reaction with water. However, the hydrate corresponding to the salt when reacts with water there is an exothermic reaction which results in a decrease in solubility with the rise in temperature.
(iii) Copper(II)sulphate.
When water is added to any anhydrous compound, it reverses back into the pentahydrate form, regaining its blue colour, and is known as blue vitriol.