Question

The following reactions are carried out with HCl(aq) containing some tritium ( \(_{1}^{3} \mathrm{H}\) ) as a tracer. Would you expect any of the tritium radioactivity to appear in the \(\mathrm{NH}_{3}(\mathrm{g}) ?\) In the \(\mathrm{H}_{2} \mathrm{O} ?\) Explain. $$\begin{array}{c} \mathrm{NH}_{3}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow \mathrm{NH}_{4} \mathrm{Cl}(\mathrm{aq}) \\ \mathrm{NH}_{4} \mathrm{Cl}(\mathrm{aq})+\mathrm{NaOH}(\mathrm{aq}) \longrightarrow\\\\\mathrm{NaCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(1)+\mathrm{NH}_{3}(\mathrm{g})\end{array}$$

Short answer

Yes, we would expect the tritium radioactivity to appear in both the \( NH_3(g)\) and \( H_2O(l)\). This is because the tritium in the HCl(aq) could end up as part of the \( NH_4+\) ion in the first reaction, which then can be part of both \( NH_3(g)\) and \( H_2O(l)\) in the results of the second reaction.

Step-by-step solution

Analyze the chemical reactions

The first thing to do is to understand each chemical reaction. In the first reaction, \( NH_3(aq)\) and \( HCl(aq)\) combine to form \( NH_4Cl(aq)\). In the second reaction, \( NH_4Cl(aq)\) reacts with \( NaOH(aq)\) to produce \( NaCl(aq)\), \( H_2O(l)\) and \( NH_3(g)\)

Understand the role of the tracer

Next, focus on where the tritium, which is a tracer in the HCl(aq), would end up in the products of the reactions. When \( HCl(aq)\) reacts with \( NH_3(aq)\) to form \( NH_4Cl(aq)\), the tritium in HCl could end up in the NH4+ ion as the hydrogen part of the HCl becomes part of the NH4+.

Understand the second reaction

In the second reaction, \( NH_4Cl\) then reacts with \( NaOH\) to produce \( NaCl(aq)\), \( H_2O (l)\) and \( NH_3(g)\). In this reaction, it's crucial to understand that \( NH_4+\) ion breaks apart. This means the tritium, if it was part of the ammonia in the \( NH_4+\) ion, could be released as \( NH_3(g)\). The other product, \( H_2O\), also contains hydrogen atoms, which means the tritium could end up here as well. Hence, tritium radioactivity should appear in both \( NH_3(g)\) and \( H_2O(l)\).

Key concepts

Chemical Reactions

Chemical reactions involve the reorganization of atoms that leads to the formation of new substances. In our exercise, we look at two reactions. First, an acid-base reaction where ammonia ( H_3(aq) ) and hydrochloric acid ( HCl(aq) ) react to produce ammonium chloride ( NH_4Cl(aq) ). In this process, the hydrogen ion from HCl combines with the ammonia to form the ammonium ion ( NH_4^+ ).
The second is another acid-base reaction where NH_4Cl(aq) reacts with sodium hydroxide ( NaOH(aq) ). This reaction results in the production of sodium chloride ( NaCl(aq) ), water ( H_2O(l) ), and releases NH_3(g) . Notably, in both reactions, hydrogen ions play a key role, being transferred from one molecule to another. This is why it is crucial to trace the hydrogen atoms, especially when dealing with tritium as a tracer.

Radioactive Tracers

Radioactive tracers are a unique tool in chemistry that help track where elements move in a reaction. Tritium ( _{1}^{3} H ) is a radioactive isotope of hydrogen used as a tracer here. When included in a reactant, it can suggest where hydrogen atoms end up in the products.
In our example, tritium is initially part of the HCl(aq) . As chemical reactions occur, the tritium exchanges locations as hydrogen atoms are transferred. When HCl a reacts with NH_3(aq) , the tritium can move to the ammonium ion ( NH_4^+ ). As the reaction proceeds to the formation of NaCl(aq) , H_2O(l) , and NH_3(g) , tritium remains where hydrogen is present, often being released in the NH_3(g) or in H_2O(l) , demonstrating the movement and transformation of hydrogen atoms.

Hydrogen Isotopes

Hydrogen isotopes are atoms of hydrogen with differing numbers of neutrons. The most common is protium, with no neutrons. Deuterium has one, and tritium ( _{1}^{3} H ) has two. It's these additional neutrons that give tritium its radioactive properties.
In chemical reactions, isotopes generally behave alike because they have the same number of electrons, which determine chemical behavior. Therefore, tritium as an isotope of hydrogen will react similarly to its non-radioactive counterparts. However, its radioactive decay is beneficial for chemical tracking. As tritium is incorporated into products like NH_3(g) or H_2O(l) , it allows chemists to track the path of the hydrogen it represents, providing essential insights into reaction mechanisms.