Question

What is the oxidation state of calcium in calcium carbonate ($$CaC{O}_3$$ )?
A. $+6$
B. $+5$
C. $+4$
D. $+1$
E. $+2$

Answer 1

Hint:Oxidation state explains the degree of oxidation for an atom in any chemical compound. It is the imaginary charge that would occur on an atom if all the bonds associated with the atoms of different elements were imagined to be completely ionic. Oxidation states can be generally represented by the integers, which can either be positive, negative, or zero.

Complete step by step answer:

In order to determine the oxidation state of any atom in a particular compound, the oxidation state of the other atoms that form the compound, must be known. Thus, let us determine the oxidation state of the calcium atom in calcium carbonate step by step.
(i) The oxidation state of carbon is determined to be $$+4$$ as it has four valence electrons and can readily lose four electrons to attain the nearest noble gas configuration. Along with that, it is surrounded by three oxygen atoms and one calcium atom which clearly shows that all the four valence electrons are being shared by the exterior atoms.
(ii) The oxidation state of one oxygen atom is found to be $$-2$$ because the electronic configuration of an oxygen atom is $1s^{2}2s^{2}2p^4$ and it requires an additional two more electrons to complete its octet and attain the nearest noble gas configuration. But, as we can see that there are a total of three oxygen atoms in calcium carbonate, hence, the overall oxidation state of oxygen is found to be $$-6$$ .
(iii) Now, let the oxidation state of the calcium atom be $x$ . The overall charge on the compound is zero.
$x+1\times (+4)+3\times (-2)=0$
$\Rightarrow x+4-6=0$
$\Rightarrow x=+2$
Thus, the correct option is E. $+2$ .

Note:
We can even directly predict the oxidation state of calcium by simply determining the overall charge on the carbonate ion. According to the structure of the carbonate ion, the two oxygen atoms attached to the carbon atom have $$-1$$ charge over each of them. Thus, the overall charge on the carbonate ion will be $$-2$$ and counteracting that, the calcium atom will have an oxidation state of $$+2$$ .