Question

Sodium chromate (VI), $N{{a}_{2}}Cr{{O}_{4}}$ is manufactured by heating chromite, $FeC{{r}_{2}}{{O}_{4}}$with sodium carbonate in an oxidizing atmosphere. Chromite contains $C{{r}_{2}}{{O}_{4}}^{2-}$ ions.
$2FeC{{r}_{2}}{{O}_{4}}+4N{{a}_{2}}C{{O}_{3}}+3\frac{1}{2}{{O}_{2}}\to 4N{{a}_{2}}Cr{{O}_{4}}+F{{e}_{2}}{{O}_{3}}+4C{{O}_{2}}$
What happens in this reaction?
(A) Chromium and iron are the only elements oxidized.
(B) Chromium, iron and carbon are oxidized.
(C) Only chromium is oxidized.
(D) Only iron is oxidized.

Answer 1

Hint: As we know that sodium chromate is manufactured by heating chromite with sodium carbonate in an oxidizing atmosphere which means it is a redox reaction. It is a type of chemical reaction in which the oxidation states of atoms are changed which is due to the transfer of electrons from one chemical species to the other that participates in the same reaction.

Complete answer:
Let us first discuss the concept of redox reaction as follows:-
-Redox reaction: It is a category of chemical reaction in which the oxidation states of a molecule, atom, or ion changes by gaining or losing electrons or we can say that it is a type of reaction that involves a transfer of electrons between two species.
-It can either be reduction or oxidation of the species during the reaction. This can be checked by comparing the oxidation state of atoms of each reactant side to its product side.
-Now let us check the oxidation state of each atom in the given reaction as follows:-
$2FeC{{r}_{2}}{{O}_{4}}+4N{{a}_{2}}C{{O}_{3}}+3\frac{1}{2}{{O}_{2}}\to 4N{{a}_{2}}Cr{{O}_{4}}+F{{e}_{2}}{{O}_{3}}+4C{{O}_{2}}$

Oxidation state of atom on reactant side:-	Oxidation state of atom on product side:-
Fe = +2	Fe = +3
Cr = +3	Cr = +6
Na = +1	Na = +1
C = +4	C = +4
O = -2	O = -2

As we can see that the oxidation state of iron (Fe) changed from +2 to +3 and the oxidation state of chromium (Cr) changed from +3 to +6 whereas sodium (Na), carbon (C) and oxygen (O) has the same oxidation state. So, only Fe and Cr get oxidized in the given reaction.
-From the above data we can conclude that in the given reaction (A) Chromium and iron are the only elements oxidized.

Note:
-Remember to study and learn the concept of the redox reaction and also understand everything regarding the oxidation state of atoms in each compound as they play an important role in calculation of various concentration terms.
-Oxidation can be described as loss of electrons or addition of oxygen and loss of hydrogen atom whereas reduction can be described as gain of electrons or addition of hydrogen and loss of oxygen atom.