Question

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.

Short answer

Use \(\mathrm{NaOH}\); it reacts with \(\mathrm{NH}_{4} \mathrm{Cl}\) to produce ammonia gas, while \(\mathrm{KCl}\) shows no reaction.

Step-by-step solution

Understanding the compounds

Both potassium chloride (\(\mathrm{KCl}\)) and ammonium chloride (\(\mathrm{NH}_{4} \mathrm{Cl}\)) are salts that appear as white solids. However, they contain different ions: \(\mathrm{KCl}\) contains \(\mathrm{K}^+\) and \(\mathrm{Cl}^-\), while \(\mathrm{NH}_{4} \mathrm{Cl}\) contains \(\mathrm{NH}_{4}^+\) and \(\mathrm{Cl}^-\). The strategy is to find a reagent that reacts with one of these ions to produce a noticeable difference.

Choosing the reagent - NaOH

Sodium hydroxide (\(\mathrm{NaOH}\)) is a suitable reagent. When added to \(\mathrm{NH}_{4} \mathrm{Cl}\), it will react to release ammonia gas (\(\mathrm{NH}_{3}\)), which has a distinct smell. The reaction is: \(\mathrm{NH}_{4}^+ + \mathrm{OH}^- \rightarrow \mathrm{NH}_{3(g)} + \mathrm{H}_2\mathrm{O}\). In contrast, \(\mathrm{KCl}\) does not react with \(\mathrm{NaOH}\) to release a gas or produce a smell, thus allowing you to distinguish between them.

Testing the reaction with NH4Cl

Add \(\mathrm{NaOH}\) to \(\mathrm{NH}_{4} \mathrm{Cl}\). You will observe the release of ammonia gas, which can be confirmed by its characteristic pungent smell. \(\mathrm{NH}_{4} \mathrm{Cl} + \mathrm{NaOH} \rightarrow \mathrm{NH}_{3}(\text{g}) + \mathrm{NaCl} + \mathrm{H}_2\mathrm{O}\).

Testing the reaction with KCl

Add \(\mathrm{NaOH}\) to \(\mathrm{KCl}\). You will observe no reaction and no gas is released. \(\mathrm{KCl}\) remains unchanged, confirming its presence since no smell is detected.

Key concepts

KCl properties

Potassium chloride (KCl) is a fairly common compound that you might find in various applications, such as being a part of fertilizers or even as a substitute for table salt in certain diets. It is important to understand that KCl consists of two ions: potassium ions (\( \mathrm{K}^+ \)) and chloride ions (\( \mathrm{Cl}^- \)).

**Appearance**
KCl is a white crystalline solid. This appearance is quite typical for salts and is shared with other compounds, including \( \mathrm{NH}_4\mathrm{Cl} \), which can sometimes make visual identification difficult.

**Non-reactivity with NaOH**
When it comes to chemical reactions, KCl is quite stable. This stability is important when distinguishing it from NH4Cl using \( \mathrm{NaOH} \). When NaOH is added to KCl, there is no visible reaction; no gas is released, and the solution remains unchanged. This inert behavior towards NaOH is key when differentiating between KCl and NH4Cl.

Knowing the properties of KCl helps in recognizing it in various mixtures and understanding its behavior in reactions.

NH4Cl properties

Ammonium chloride (NH4Cl) is another commonly encountered white crystalline solid, consisting of ammonium ions (\( \mathrm{NH}_4^+ \)) and chloride ions (\( \mathrm{Cl}^- \)). Despite its similar appearance to KCl, NH4Cl has distinct properties that set it apart, particularly in chemical reactions.

**Basic Use and Behavior**

• NH4Cl is used in several applications, including as a nitrogen supply in fertilizers and in some cold medications as an expectorant.
• It dissolves easily in water and has interesting thermal properties, such as sublimation upon heating.

**Reactivity with NaOH**
One of the most telling reactions for NH4Cl is with sodium hydroxide (NaOH). When NaOH is added to a solution of NH4Cl, it reacts to form ammonia gas (\( \mathrm{NH}_3 \)), which is easy to identify due to its distinctive pungent smell. The reaction can be represented as: \( \mathrm{NH}_4^+ + \mathrm{OH}^- \rightarrow \mathrm{NH}_3(g) + \mathrm{H}_2\mathrm{O} \). This chemical property is particularly useful for distinguishing NH4Cl from KCl.

Being aware of these properties makes it easier to recognize NH4Cl in a reaction and understand how it behaves when mixed with other substances.

NaOH reactivity

Sodium hydroxide, commonly known as NaOH, is a strong base widely used in industries and laboratories. Its reactivity is a crucial aspect that makes it useful in distinguishing between different chemical compounds.

**Reactions with Common Compounds**
NaOH is well-known for its ability to react with acids and certain salts. When added to NH4Cl, as earlier noted, it produces ammonia gas, characterized by a pungent odor. This reactivity is crucial for differentiating NH4Cl from KCl, which remains unreactive and does not release gas when treated with NaOH.

**Handling and Safety**

• NaOH is highly caustic and can cause severe burns, so it should be handled with care.
• In a laboratory setting, protective gear such as gloves and goggles are essential when working with NaOH.

Understanding NaOH's reactivity is important for safely conducting laboratory experiments and accurately identifying compounds based on their reactions. Its ability to differentiate NH4Cl from KCl is just one example of its usefulness in practical chemistry applications.