Why is it necessary to know the chemical composition of salt?

Answer 1

Ordinary table salt, NaCl, consists mainly of Sodium (Na+) and chloride (Cl-) ions. Nowadays, a small amount of Iodide (about 0.5 g/100g) is also added after it was discovered in Britain that the lack of Iodine caused diseases. Without knowing the chemical composition of salt, there is no guarantee for the consumers what the salt is made up of, or of the purity of the salt. Other than this, knowing the crystalline structure of any type of salt might be of vital importance in a lot of different genres, such as in lasers, optic lenses, piezo electronics, computers etc. The key to understanding the materials themselves are to be able to break down their existence into their basic building blocks, analyse these, and from these results draw conclusions and predictions that might bring research forward.

The composition of salt are, of course, varying, for each different compound (NaCl is not the same as CaF2, for example), and the composition of the same type of salts are also known to locally carry some defects (mainly induced by displacement reactions, where an ion jumps from one position to another, leaving the normal type structure and thus also breaking the stoichiometry). This baffeled scientists at first, because the stoichiometry of a reaction had previously been considered absolute, meaning no consideration had been taken to deal with these "defects" noticed in the crystal salts:

x A + y B → AxBy (normal structure, e.g. Rock-salt)

NOT

x A + y B → A(x+0.05)B0.95y (still rock-salt, but because of the defects, some ions of y have been misplaced from the unit cell, while there is a small excess of A ions).

Anyhow, as previously stated, knowing the chemical composition of salts is key to determining what possible applications and implementations might come out of studying it in the future simply because we usually won't know much before we have conducted an experiment or simulation at least.