Animated Solution for Chemistry - Organic Chemistry: Comprehension Passage

Have you ever looked at a chemical reaction and realized it's actually a beautifully choreographed dance of electrons? This problem is a perfect example of that. We are given a two-step process where a simple metal, tin, ultimately transforms a nitro group into an amine salt. Let's break down this fascinating sequence and uncover the hidden stoichiometry.

The problem begins with a classic inorganic reaction: the reaction of tin ($\text{Sn}$) with hydrochloric acid ($\text{HCl}$). When a metal like tin is dropped into an acid, it dissolves to form a salt, releasing hydrogen gas in the process.

The reaction is:

Here, tin is oxidized from an oxidation state of $0$ to $+2$, forming tin(II) chloride (${\text{SnCl}}_2$). This ${\text{SnCl}}_2$ is not just any salt; it is a potent reducing agent, hungry to give away more electrons and reach its stable $+4$ oxidation state.

Now, the narrative shifts to organic chemistry. The entire amount of this ${\text{SnCl}}_2$ is reacted with nitrobenzene (${\text{C}}_6{\text{H}}_5{\text{NO}}_2$) in the presence of more $\text{HCl}$.

Nitrobenzene is eager to be reduced. The nitro group ($-{\text{NO}}_2$) will accept electrons and protons to become an amine group ($-{\text{NH}}_2$). However, there is a crucial catch here! Because the reaction is taking place in a highly acidic medium (excess $\text{HCl}$), the basic aniline formed will immediately get protonated.

Instead of free aniline, we get an organic salt: anilinium chloride (${\text{C}}_6{\text{H}}_5{\text{NH}}_3^{+}{\text{Cl}}^{-}$).

Let's look at the electron exchange. The nitrogen in nitrobenzene goes from an oxidation state of $+3$ to $-3$ in the amine, requiring $6$ electrons. Each ${\text{Sn}}^{2+}$ ion can only provide $2$ electrons as it oxidizes to ${\text{Sn}}^{4+}$. Therefore, we need exactly $3$ moles of ${\text{SnCl}}_2$ to fully reduce $1$ mole of nitrobenzene.

The balanced equation for this second step is:

With the chemistry fully decoded, the math becomes incredibly straightforward. We are told that $1.29\text{ g}$ of the organic salt (anilinium chloride) is produced.

First, let's find its molar mass. The formula is ${\text{C}}_6{\text{H}}_5{\text{NH}}_3\text{Cl}$:

This makes our calculation beautifully simple. The number of moles of the organic salt is:

From our balanced equation, $1$ mole of nitrobenzene produces $1$ mole of anilinium chloride. Therefore, the moles of nitrobenzene required must also be $0.01\text{ mol}$.

To find the mass of nitrobenzene ($y$), we multiply its moles by its molar mass ($123{\text{ g mol}}^{-1}$):

Finally, let's trace back to the tin. We established that $3$ moles of ${\text{SnCl}}_2$ are needed for every mole of nitrobenzene. Since $1$ mole of $\text{Sn}$ produces $1$ mole of ${\text{SnCl}}_2$, we need $3$ moles of $\text{Sn}$ for every mole of nitrobenzene.

To find the mass of tin ($x$), we multiply its moles by its atomic mass ($119{\text{ g mol}}^{-1}$):

And just like that, by carefully following the electrons and the protons, we have unraveled the entire sequence. The values are $x=3.57$ and $y=1.23$. Chemistry is truly a puzzle where every piece fits perfectly!