MnO$_4$(aq) + Y + 5Fe$^{2+}$ (aq) $\mapsto$ Mn$^{2+}$ (aq) + 5Fe$^{3+}$ (aq) + 4H$_2$O (l). In the equation above, Y is

To solve this problem, we need to apply the Law of Conservation of Mass, which states that the number of atoms of each element must be the same on both sides of a chemical equation.

1. Analyze the Equation

The given equation is: MnO$_4^-$ (aq) + Y + 5Fe$^{2+}$ (aq) $\rightarrow$ Mn$^{2+}$ (aq) + 5Fe$^{3+}$ (aq) + 4H$_2$O (l)

We need to determine the value of Y by balancing the atoms that are currently unbalanced.

2. Explain the Concept

In redox reactions occurring in acidic media, we balance the oxygen atoms by adding water (H$_2$O) to the side deficient in oxygen. Then, we balance the hydrogen atoms by adding hydrogen ions (H$^+$) to the opposite side.

3. Step-by-Step Solution

• Step 1: Check the Oxygen atoms. • Left side: There are 4 oxygen atoms in MnO$_4^-$. • Right side: There are 4 oxygen atoms in 4H$_2$O. • Oxygen is balanced.

• Step 2: Check the Hydrogen atoms. • Right side: There are 4 molecules of H$_2$O, which means $4 \times 2 = 8$ hydrogen atoms. • Left side: To have 8 hydrogen atoms, Y must contain 8H$^+$.

• Step 3: Verify the Charge (Optional but recommended). • Left side: $(-1) + 8 + 5(+2) = -1 + 8 + 10 = +17$ • Right side: $(+2) + 5(+3) = 2 + 15 = +17$ • Since the charges are balanced, our identification of Y is correct.

4. Identify the Answer

Comparing our result to the options provided, Y must be 8H$^+$ (aq). This matches option C.

5. Exam Tip

When balancing redox equations in JAMB Chemistry, always remember the "OH-Charge" sequence:

1. Balance the main element (Mn and Fe).
2. Balance Oxygen by adding H$_2$O.
3. Balance Hydrogen by adding H$^+$.
4. Balance the Charge by adding electrons (e$^-$). If you follow this order, you will rarely make a mistake!