Question

The equivalent weight of carbonate is 30 g.eq. Then, its valency is:

Answer 1

Hint: The atomic weight of a compound is the product of its valency and equivalent weight. Thus, we can easily find the valency if we know the equivalent weight and calculate the molecular weight from the periodic table of elements.

Complete step by step solution:
Valency or Valence factor refers to the valency in element, acidity of bases, basicity of acids and total charge of cation or anion in an ionic compound.
It is the ability of an atom or a group of atoms to combine with other atoms. The valency is determined by the number of electrons that an atom can gain, lose or share.
It is the ions or the combining atoms making up the compound that have different valencies and these valencies give rise to different chemical formulae for different components.
For ions, the valency is equal to the charge possessed by the molecule.
We know,
\[Valency\,=\,\dfrac{Atomic\,weight}{Equivalent\,weight}\]
First we need to calculate the atomic weight of Carbonate ($CO_3$)
Atomic weight = (1 $\times$ mass of C) + (3 $\times$ mass of O)
= (1x12) + (3x16)
=12+48
=60 g
Now, we substitute the values in the equation:
\[Valency\,=\,\dfrac{60}{30}\,=\,2\]
Hence, the answer is 2.

Note: We must not confuse valency and oxidation number as there is a difference between them. Valency is the property of an isolated atom while the oxidation number is for an atom in a bonded state in a molecule.
We must remember that valency is a combining capacity, it does not have +or - charge, while oxidation number shows whether it can gain (+ve charge) or lose (-ve charge) electrons.