H2S (5 moles) reacts completely with acidified aqueous potassium permanganate solution. In this reac

Q: Why does KMnO4 reduce to Mn2+ and not MnO2?

The reduction product of KMnO4 depends on the medium. In an acidic medium, it reduces to Mn2+. In a neutral or faintly alkaline medium, it reduces to MnO2.

Q: How do we know H2S oxidizes to elemental sulfur?

H2S is a strong reducing agent. When reacted with a strong oxidizing agent like KMnO4, the sulfide ion (S2-) is typically oxidized to elemental sulfur (S).

Q: Why do we multiply the half-reactions by 2 and 5?

To ensure the number of electrons lost in oxidation equals the number of electrons gained in reduction. The lowest common multiple of 2 and 5 is 10.

Q: Do we need to balance the hydrogen atoms to find 'x'?

Not necessarily. Once you balance the oxygen atoms from the 2 moles of MnO4- by adding 8 H2O molecules, you have found 'x'. Balancing hydrogen just completes the full equation.

Q: What does 'moles of electrons involved' mean?

It refers to the total number of electrons transferred from the reducing agent to the oxidizing agent in the balanced stoichiometric equation.

Question

$	ext{H}_2	ext{S}$ (5 moles) reacts completely with acidified aqueous potassium permanganate solution. In this reaction, the number of moles of water produced is x, and the number of moles of electrons involved is y. The value of (x + y) is ____.

Sigma Percentile · Accepted Answer

### The Beauty of Redox Reactions

Imagine a microscopic battlefield where atoms are constantly trading electrons. This is the essence of a redox reaction.

In our problem, we are looking at the reaction between hydrogen sulfide ($	ext{H}_2	ext{S}$) and acidified potassium permanganate ($	ext{KMnO}_4$).

Potassium permanganate is a notorious electron thief—a powerful oxidizing agent. Hydrogen sulfide, on the other hand, is more than willing to give up its electrons, acting as the reducing agent.

### Decoding the Oxidation States

To understand exactly what is happening, we need to track the electrons. We do this by assigning oxidation states to the key elements involved.

Let's start with manganese in the permanganate ion ($	ext{MnO}_4^-$). Oxygen is typically at $-2$, and since the overall ion has a $-1$ charge, manganese must be at a highly oxidized state of $+7$.

In an acidic medium, this $	ext{Mn}^{+7}$ is hungry for electrons and gets reduced all the way down to $	ext{Mn}^{2+}$.

Now, let's look at sulfur in hydrogen sulfide ($	ext{H}_2	ext{S}$). Hydrogen is at $+1$, which puts sulfur at $-2$.

During the reaction, sulfur loses electrons and is oxidized to elemental sulfur ($	ext{S}$), which has an oxidation state of $0$.

### The Dance of Electrons

Now we can see the exact exchange rate of electrons.

Each manganese atom goes from $+7$ to $+2$, meaning it **gains 5 electrons**.

$$ 	ext{Mn}^{+7} + 5e^- ightarrow 	ext{Mn}^{2+} $$

Meanwhile, each sulfur atom goes from $-2$ to $0$, meaning it **loses 2 electrons**.

$$ 	ext{S}^{-2} ightarrow 	ext{S}^0 + 2e^- $$

### Balancing the Equation

Nature demands balance; the number of electrons lost must exactly equal the number of electrons gained.

To achieve this, we find the lowest common multiple of 5 and 2, which is 10. We multiply the manganese half-reaction by 2, and the sulfur half-reaction by 5.

$$ 2	ext{Mn}^{+7} + 10e^- ightarrow 2	ext{Mn}^{2+} $$

$$ 5	ext{S}^{-2} ightarrow 5	ext{S}^0 + 10e^- $$

This tells us two crucial things. First, the total number of electrons transferred in the balanced reaction is 10. Therefore, **our value for $y$ is 10**.

Second, the balanced equation requires exactly 5 moles of $	ext{H}_2	ext{S}$, which perfectly matches the condition given in the question!

### The Final Tally

With the electrons balanced, we must now balance the oxygen atoms.

We have 2 moles of $	ext{MnO}_4^-$, which gives us a total of 8 oxygen atoms on the reactant side.

To balance these in an acidic medium, we add water molecules to the product side. We need exactly 8 molecules of $	ext{H}_2	ext{O}$ to account for the 8 oxygen atoms.

Therefore, the number of moles of water produced is 8. **Our value for $x$ is 8**.

The question asks for the sum of $x$ and $y$.

$$ x + y = 8 + 10 = 18 $$

The final answer is **18**.

Animated Solution for Chemistry - Redox Reactions: $H_{2} S$ (5 moles) reacts completely with acidified aqueous potassium permanganate solution. In this reaction, the number of moles of water produced is x, and the number of moles of electrons involved is y. The value of (x + y) is ____.

Enter Numerical Value:

Visualized Solution

\text{Redox Reaction Setup}

\text{Oxidation States}

\text{Electron Transfer}

\text{Balancing Electrons}

\text{Balancing Oxygen}

\text{Final Calculation}

\text{Effect of Medium}

The Sigma Insight: Chemical Equation Balancing

The Beauty of Redox Reactions

Decoding the Oxidation States

The Dance of Electrons

Balancing the Equation

The Final Tally

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