Question

Write the ionic equation showing the oxidation of Fe(II) salt by acidified dichromate solution.

Answer 1

Hint: The redox reactions occur such that one atom gets oxidized while the other atom gets reduced. The oxidized atom loses electrons to become a cation while the reduced atom gains electrons to become anion. The overall electrons transferred remain the same.

Complete step by step solution:
-Based on the property of the compounds being able to dissociate into their ions, they are classified in 2 groups- electrolytes and non-electrolytes. Electrolytes are further classified as strong and weak electrolytes.
-Electrolyte is a compound which dissociates into its constituent ions, cation and anion in presence of DC current under the process of electrolysis.
-Many types of compound can be used as electrolytes but the most preferred compounds are acids, bases and salts. The electrolytes give redox reactions for dissociation into their ions.
-Electrolysis is a technique used to separate a compound in its different constituents with the help of DC current. It is used in non-spontaneous chemical reactions.
-The amount of voltage to be given depends on the type of the electrolyte used. The voltage is called decomposition potential.
-There are two electrodes, cathode and anode dipped in the electrolyte. They are connected to the battery. In acidified water, water is mixed with dilute sulfuric acid. This mixture acts as electrolyte.
-Cathode is the electrode where the cations are attracted. Reduction takes place at cathode. Anode is the electrode where the anions are attracted. Oxidation takes place at anode.
-There are two types of agents. One is the oxidizing agents and the other is the reducing agents. Oxidizing agents are those which oxidize the other atom by reducing themselves. Reducing agents are those that reduce the other atom by oxidizing themselves.
-Iron gets oxidized from iron(II) to iron(III). The reaction can be shown as $F{{e}^{2+}}-1{{e}^{-}}\to F{{e}^{3+}}$
Dichromate ion has multiple valences and the maximum valency for it is +6. It gains electrons in the process and oxidizes iron by reducing itself and the reaction can be given as

\[C{{r}_{2}}{{O}_{7}}^{-2}\left( aq \right)+14{{H}^{+}}\left( aq \right)+6{{e}^{-}}\to 2C{{r}^{+3}}\left( aq \right)+7{{H}_{2}}O\left( l \right)\]
-Iron loses 1 electron per mole while dichromate ion gains 6 electrons per mole. So the reaction needs to be balanced by equalizing the number of electrons on both the sides. The overall balanced reaction can be shown as
\[C{{r}_{2}}{{O}_{7}}^{-2}\left( aq \right)+14{{H}^{+}}\left( aq \right)+6F{{e}^{2+}}\to 2C{{r}^{+3}}\left( aq \right)+7{{H}_{2}}O\left( l \right)+6F{{e}^{3+}}\left( aq \right)\]

Therefore, the above equation represents the ionic equation showing the oxidation of Fe(II) salt by acidified dichromate solution.

Note: If there are metals which have variable valencies like copper and iron, they have different strengths of their reducing capabilities. Example - Copper is a better reducing agent when it is in (II) form rather than (I) form. So always take care of such metals while observing the reducing power.