Question

On passing a gas, ‘X’, through Nessler’s reagent, a brown precipitate is obtained. The gas ‘X’ is

• A. $\text{H}_2\text{S}$
• B. $\text{CO}_2$
• C. $\text{NH}_3$
• D. $\text{Cl}_2$

Answer 1

The Correct Option is C

To determine which gas 'X' produces a brown precipitate with Nessler's reagent, we will analyze the reagent's reaction and evaluate the given options.

Nessler's Reagent Reaction:

Nessler's reagent is used for the detection of ammonia (\(\text{NH}_3\)). The reaction of ammonia gas with Nessler's reagent yields a brown precipitate of mercuric amido-iodide, signifying the presence of ammonia.

The reaction equation is:

\(\text{NH}_3 + 2\text{K}_2\text{HgI}_4 + 3\text{KOH} \rightarrow \text{HgO}\cdot\text{Hg(NH}_2\text{I}) + 7\text{KI} + 2\text{H}_2\text{O}\)

Option Analysis:

• \(\text{H}_2\text{S}\): Hydrogen sulfide does not produce a brown precipitate with Nessler's reagent. It typically forms black metal sulfides with metal ions.
• \(\text{CO}_2\): Carbon dioxide does not react with Nessler's reagent to form a precipitate.
• \(\text{NH}_3\): This gas reacts with Nessler's reagent, resulting in a brown precipitate indicative of ammonia.
• \(\text{Cl}_2\): Chlorine does not react with Nessler's reagent to produce a brown precipitate.

Consequently, the gas that reacts with Nessler's reagent to form a brown precipitate is \(\text{NH}_3\).

Conclusion:

Gas 'X' that yields a brown precipitate with Nessler's reagent is identified as \(\text{NH}_3\), which is ammonia.