Question

H₂S (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 ____.

Answer 1

Correct Answer: 18

Redox Equation and Calculation 

We commence with the equilibrium redox equation:

\[2KMnO_4 + 3H_2SO_4 + 5H_2S \rightarrow K_2SO_4 + 2MnSO_4 + 5S + 8H_2O\]

We aim to determine the quantity of water molecules (\(x\)) generated and the quantity of electrons (\(y\)) engaged in this reaction.

Upon examining the balanced equation, it is evident that 8 moles of water are produced during the reaction. Hence, we can conclude:

\(x = 8\)

In this reaction, hydrogen sulfide (\(H_2S\)) undergoes oxidation to form sulfur (\(S\)). Each molecule of \(H_2S\) loses 2 electrons during this transformation (as sulfur transitions from an oxidation state of -2 in \(H_2S\) to 0 in \(S\)).

Consequently, for every mole of \(H_2S\), 2 moles of electrons are implicated. Given that 5 moles of \(H_2S\) are participating in the reaction, the overall number of moles of electrons involved amounts to:

\(5 \times 2 = 10\)

Thus, we can affirm:

\(y = 10\)

We are tasked with determining the sum of \(x\) and \(y\), so by adding these two values together, we obtain:

\(x + y = 8 + 10 = 18\)

Therefore, \(x + y = 18\).