Question

Which species is acting as a reducing agent in the following reaction?
\[14{{H}^{+}}+C{{r}_{2}}O_{7}^{2-}+3Ni\,\to \,2C{{r}^{3+}}+7{{H}_{2}}O+3N{{i}^{2+}}\]
(A) $C{{r}_{2}}O_{7}^{2-}$
(B) $Ni$
(C) ${{H}^{+}}$
(D) ${{H}_{2}}O$

Answer 1

Hint: It is a transition metal. It is hard and ductile. It has a silvery-white luster. Its atomic mass is 28. It is used in making alloys such as stainless steel.

Complete step by step solution:
To answer this question, first we should know what a reducing agent is:
Let’s take a look at the definitions of
-Reduction: It is a chemical reaction in which one of the atoms gains electrons and decreases their oxidation state while the other atom loses the electron.
-Oxidation: It is a chemical reaction in which one of the atom loses electron and increase their oxidation state while the other atom gains electron,
-Reducing Agent: It is an element which easily loses electrons and reduces its oxidation state. Generally metals are good reducing agents.
-Oxidizing Agent: It is an element which easily gains electrons and increases its oxidation state. Generally non-metals are good oxidizing agents.
Now, we know that Ni is a transition metal and it easily loses electron to come to its stable configuration which is in +2 oxidation state.
In the given reaction Ni acts as the reducing agent. It reduces dichromate ion. Hence, Ni is the reducing agent in the above redox reaction.

So, the answer for the given question is option (B).

Note: Metals have low ionization energy and complete their octet by losing electrons. This makes them a good reducing agent. As the size of metals increases down the group, their reducing character also increases. Dichromate is a mild oxidizing agent and it is used to convert primary alcohols into aldehydes.