Question

Which of the following are efflorescent substances?
A. $CuS{O_4}.5{H_2}O$
B. $N{a_2}C{O_3}.10{H_2}O$
C. ${K_2}S{O_4}A{l_2}{(S{O_4})_3}.24{H_2}O$
D. ${\left( {N{H_4}} \right)_2}S{O_4}$

Answer 1

An efflorescent substance is a chemical compound that has water molecules associated with its crystal, and when it is exposed to air, loses this water through evaporation. A common example of this phenomenon is the drying of cement.

Complete step by step answer:
$CuS{O_4}.5{H_2}O$ is a blue color compound. When $CuS{O_4}.5{H_2}O$ is exposed to air it evaporates the water molecules of crystallization and forms a white color crystalline compound.
When $N{a_2}C{O_3}.10{H_2}O$ is exposed to air, at first it evaporates 9 water molecules after that it evaporates all molecules of water and becomes anhydrous.

So, the correct answer is A and B.

Additional information:
When Sulphur is boiled with $N{a_2}{S_2}{O_3}$ a solution, the compound formed is sodium thiosulphate.
The reaction is as shown,
$8N{a_2}{S_2}{O_3} + S \to 8N{a_2}{S_2}{O_3}$
Sodium thiosulphate is an inorganic compound. Typically, it is available as the white or colorless pentahydrate, $N{a_2}{S_2}{O_3}.5{H_2}O$ .
The solid is an efflorescent crystalline substance that dissolves well in water.
It is a reducing agent and is often used to control the reductive-oxidative properties of the sulfide mineral surface during floatation. It is used to reduce iodine back to iodide before iodine can complex with the starch to form the characteristic blue-black color.

Note: The chemical formula of soda ash is $N{a_2}C{O_3}$ . Soda ash is also known as washing soda or soda crystals. Baking soda is known as sodium bicarbonate. Soda ash is also known as washing soda or soda crystals. It is used to produce glass, soap, paper, etc. in industry, as a detergent ingredient, as a medicinal ingredient and also used in photography, etc. soda ash is also used to remove the hardness of water by the formation of insoluble carbonates of the ions present in the water.