Both \(\mathrm{KCl}\) and \(\mathrm{NH}_{4} \mathrm{Cl}\) are white solids. Suggest one reagent that would enable you to distinguish between these two compounds.

Understanding the chemical properties of salts is crucial when we attempt to distinguish between compounds such as potassium chloride (KCl) and ammonium chloride (NH₄Cl). Salts are ionic compounds that are formed by the chemical combination of cations (positively charged ions) and anions (negatively charged ions). In general, salts are known for their high melting points, electrical conductivity when molten or in solution, and their ability to form crystals.

KCl, a salt composed of potassium ions (K+) and chloride ions (Cl-), showcases properties typical of ionic salts, including solubility in water and stability under heat. Unlike KCl, NH₄Cl consists of the ammonium ion (NH₄+) paired with a chloride ion (Cl-). Despite also being an ionic compound, NH₄Cl exhibits distinct chemical behavior upon heating, which facilitates its identification. Therefore, understanding these foundational chemical properties enables us to predict and explain the behavior of these salts under various conditions.

The decomposition of ammonium chloride (NH₄Cl) is a key reaction that occurs when this compound is heated. Unlike KCl, which remains stable when exposed to heat, NH₄Cl undergoes thermal decomposition according to the chemical equation:\[\begin{equation}NH_4Cl(s) \rightarrow NH_3(g) + HCl(g)\end{equation}\]This reaction can be visualized as the breaking apart of the ammonium ion into ammonia (NH₃) and hydrogen chloride gas (HCl). The formation of ammonia gas is a unique trait of NH₄Cl upon heating, making it one of the distinguishing factors in qualitative analysis between NH₄Cl and other salts such as KCl.

Qualitative chemical analysis is the process of determining the chemical constituents of a substance through observations and reactions, rather than quantifying the amounts present. This kind of analysis involves observing color changes, precipitation, gas evolution, and other property changes.

For example, distinguishing between KCl and NH₄Cl can be achieved through simple qualitative tests like heating the compounds. KCl, being stable, will not exhibit any change, while NH₄Cl decomposes to release gases that can be detected through further qualitative tests. The ability to understand and utilize qualitative analysis allows individuals to make informed identifications of substances in various contexts, including academic and industry settings.

Identifying the presence of ammonia gas (NH₃) is an important aspect of chemical analysis, especially when distinguishing compounds like NH₄Cl from KCl. Upon the decomposition of ammonium chloride, ammonia gas is released, which has distinct properties that allow for its detection. These properties include a characteristic pungent smell and being less dense than air.

To confirm the presence of NH₃, red litmus paper can be used as an indicator. Ammonia is a basic gas and it will turn red litmus paper blue, a property not observed with many other gases. This qualitative test not only confirms that a gas is present but directly identifies it as ammonia, reinforcing the initial hypothesis that the substance undergoing decomposition is NH₄Cl.