Question

Water Formed is tested by:
A.Copper nitrate test
B.Anhydrous copper sulphate test
C.Aqueous copper sulphate test
D.Copper

Answer 1

Hint:There are different salts that have the ability to soak the water molecules from the surroundings and these compounds are called hygroscopic salts. Any compound is called hygroscopic when it has the ability to attract water molecules and hold them in its structure.

Complete answer:
The hygroscopic nature of a salt can be used for the detection of water formed in a sample of salt. Anhydrous salts like anhydrous copper sulphate and anhydrous cobalt chloride change their colour n absorbing water molecules from the environment. The anhydrous copper sulphate salt turns blue on absorption of water molecules and cobalt chloride turns pink on absorption of water.

Hence, the correct option among the above is anhydrous copper sulphate test, option B.
Note:
When anhydrous copper sulphate absorbs water molecules then the molecules of water are trapped in the ionic lattice of the copper cations and the sulphate anions. Though the compound itself is still white, the colour change is only due to the presence of the water molecules. The water molecules act as the ligand and the oxygen atoms of these water molecules contribute their d-orbital electrons to the d-orbitals of the metal atom. The d-orbitals of the metal atom are now no longer degenerate and hence they absorb energy so that d-d transition takes place absorbing red wavelength. Therefore the complementary colour of red, which is blue is reflected by the complex.