When the following redox reaction is balanced in an acidic medium using the smallest whole… — JAMB UTME

When the following redox reaction is balanced in an acidic medium using the smallest whole-number coefficients:

\text{ClO}_3^-(\text{aq}) + a\text{Fe}^{2+}(\text{aq}) + b\text{H}^+(\text{aq}) \rightarrow \text{Cl}^-(\text{aq}) + c\text{Fe}^{3+}(\text{aq}) + d\text{H}_2\text{O}(\text{l})

What is the value of the coefficient

b

for

\text{H}^+

The stoichiometric coefficient for hydrogen ions is 6.

In the reduction half-reaction,

\text{ClO}_3^-

is reduced to

\text{Cl}^-

. Balancing the 3 oxygen atoms requires

3\text{ H}_2\text{O}

on the product side. Consequently,

6\text{ H}^+

ions are required on the reactant side to balance the 6 hydrogen atoms, giving

b = 6

Determine the oxidation state change for chlorine

\text{ClO}_3^-

, chlorine has an oxidation state of

+5

. In

\text{Cl}^-

, chlorine has an oxidation state of

-1

. The total change is a gain of

6\text{ e}^-

Knowing the electron transfer per mole of chlorate ion establishes the electron requirement for the reduction half-reaction.

Balance oxygen atoms using water

The chlorate ion

\text{ClO}_3^-

contains 3 oxygen atoms, requiring

3\text{ H}_2\text{O}

on the product side.

In acidic redox balancing, oxygen atoms are balanced by adding water molecules to the side deficient in oxygen.

Balance hydrogen atoms using hydrogen ions

To balance the 6 hydrogen atoms in

3\text{ H}_2\text{O}

, add

6\text{ H}^+

to the reactant side.

Hydrogen atoms from the water molecules on the product side must originate from hydrogen ions in the acidic medium.

Verify overall mass and charge balance

The reduction half-reaction is

\text{ClO}_3^- + 6\text{H}^+ + 6\text{e}^- \rightarrow \text{Cl}^- + 3\text{H}_2\text{O}

. Adding the oxidation half-reaction

6\text{Fe}^{2+} \rightarrow 6\text{Fe}^{3+} + 6\text{e}^-

yields the overall balanced equation with

b = 6

Combining half-reactions confirms that electrons cancel out and mass and charge are conserved.

Balancing Redox Equations via Half-Reactions in Acidic Medium

Question