Q21.11P - Chemistry: Molecular Nature Of Matter And Change

Question

Consider the following balanced redox reaction: 

${\mathbf{\text{2CrO}}}_{\mathbf{2}}^{\mathbf{-}}\left(\text{aq}\right)\mathbf{ }\mathbf{+}\mathbf{2}{\mathbf{\text{H}}}_{\mathbf{2}}\mathbf{\text{O}}\left(\text{l}\right)\mathbf{+}\mathbf{ }\mathbf{6}{\mathbf{\text{ClO}}}^{\mathbf{-}}\left(\text{aq}\right)\mathbf{\to }\mathbf{2}{\mathbf{\text{CrO}}}_{\mathbf{4}}^{\mathbf{2}\mathbf{-}}\left(\text{aq}\right)\mathbf{ }\mathbf{+}\mathbf{3}{\mathbf{\text{Cl}}}_{\mathbf{2}}\left(\text{g}\right)\mathbf{ }\mathbf{+}\mathbf{4}{\mathbf{\text{OH}}}^{\mathbf{-}}\left(\text{aq}\right)$

(a) Which species is being oxidized? 

(b) Which species is being reduced? 

(c) Which species is the oxidizing agent?

(d) Which species is the reducing agent? 

(e) From which species to which does electron transfer occur? 

(f) Write the balanced molecular equation, with the spectator ion.

Step-by-Step Solution

Answer

All the answers to every part are given and explained in the second step.

Step 1: Definition of Redox Reaction

The oxidation states of atoms are changed during redox reactions. Redox reactions are defined by the actual or formal movement of electrons between chemical species, with one species often experiencing oxidation while the other experiences reduction.

Step 2: Solution for all the parts of the question.

Given balanced redox reaction:

$2{\mathrm{CrO}}_2^{-}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+6{\mathrm{ClO}}^{-}\left(\mathrm{aq}\right)\to 2{\mathrm{CrO}}_4^{2-}\left(\mathrm{aq}\right)+3{\mathrm{Cl}}_2( \mathrm{g})+O{H}^{-}\left(aq\right)$

(a) ${\mathrm{CrO}}_2^{-}\left(\mathrm{aq}\right)$ is being oxidized as there is an increase in the oxidation state of $\mathrm{Cr} (+3\to +6)$.

(b) ${\mathrm{ClO}}^{-}\left(\mathrm{aq}\right)$ is being reduced as there is a decrease in the oxidation state of $\mathrm{Cl} (+1\to 0)$.

(c) ${\mathrm{ClO}}^{-}\left(\mathrm{aq}\right)$ is the oxidizing agent as it oxidizing ${\mathrm{CrO}}_2^{-}\left(\mathrm{aq}\right)$ to ${\mathrm{CrO}}_4^{2-}\left(\mathrm{aq}\right)$ and is itself being reduced in the process.

(d) ${\mathrm{CrO}}_2^{-}\left(\mathrm{aq}\right)$ is the reducing agent as it reducing ${\mathrm{ClO}}^{-}\left(\mathrm{aq}\right)$ to ${\mathrm{Cl}}_2( \mathrm{g})$ and is itself being oxidized in the process.

(e) Electron transfer occurs from ${\mathrm{CrO}}_2^{-}\left(\mathrm{aq}\right)$ to  ${\mathrm{ClO}}^{-}\left(\text{aq}\right)$.

(f) Balanced molecular equation, with ${\mathrm{Na}}^{+}$ as spectator ions.

$2{\mathrm{NaCrO}}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+6\mathrm{NaClO}\left(\mathrm{aq}\right)\to 2{\mathrm{Na}}_2{\mathrm{CrO}}_4\left(\mathrm{aq}\right)+3C{l}_2( \mathrm{g})+4\mathrm{NaOH}\left(\mathrm{aq}\right)$