Question

Which of the following reactions does not liberate gaseous product? (a) \(\mathrm{AlCl}_{3}+\mathrm{NaOH} \rightarrow\) (b) \(\mathrm{NaOH}+\mathrm{P}(\) white \()+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (c) \(\mathrm{Al}+\mathrm{NaOH} \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{Zn}+\mathrm{NaOH} \stackrel{\Delta}{\longrightarrow}\)

Short answer

Option (a) does not liberate a gaseous product.

Step-by-step solution

Analyze Option (a)

In reaction (a), \( \mathrm{AlCl}_{3} \) reacts with \( \mathrm{NaOH} \). Typically, this reaction would form \( \mathrm{NaAlO}_2 \), a solid, and \( \mathrm{NaCl} \). No gaseous product is expected in this reaction.

Analyze Option (b)

For reaction (b), \( \mathrm{NaOH} \) reacts with white phosphorus and water. This reaction generally produces \( \mathrm{PH}_3 \), which is phosphine, a gas. Thus, a gaseous product is liberated.

Analyze Option (c)

In reaction (c), \( \mathrm{Al} \) reacts with \( \mathrm{NaOH} \), especially when heat (\( \Delta \)) is involved. The products of this reaction include hydrogen gas (\( \mathrm{H}_{2} \)), which is a gaseous product.

Analyze Option (d)

For reaction (d), \( \mathrm{Zn} \) with \( \mathrm{NaOH} \) under heat is known to produce hydrogen gas (\( \mathrm{H}_{2} \)). Therefore, a gaseous product is liberated.

Key concepts

AlCl3 and NaOH reaction

The reaction between aluminum chloride (\( \mathrm{AlCl}_{3} \)) and sodium hydroxide (\( \mathrm{NaOH} \)) is an interesting one. Typically, when these two compounds react, they form sodium aluminate (\( \mathrm{NaAlO}_2 \)) and sodium chloride (\( \mathrm{NaCl} \)). The important thing to note here is that this reaction results in the formation of solid compounds without any liberation of gaseous substances.

This reaction primarily involves the exchange of ions, often described as a double displacement reaction. Here’s a simplified way to understand it:

• The chlorides from \( \mathrm{AlCl}_{3} \) (aluminum chloride) combine with the sodium from \( \mathrm{NaOH} \) (sodium hydroxide) to form \( \mathrm{NaCl} \) (sodium chloride).
• At the same time, the aluminum ions form a new compound with the hydroxide ions, resulting in the formation of \( \mathrm{NaAlO}_2 \) (sodium aluminate).

Therefore, no gaseous product emerges from this reaction, making it quite straightforward in its outcome.

Phosphine gas formation

When sodium hydroxide (\( \mathrm{NaOH} \)) interacts with white phosphorus (P) in the presence of water, the reaction produces phosphine gas (\( \mathrm{PH}_3 \)). The liberation of this gas is an essential outcome of the reaction.

Phosphine is notable for its gaseous state and is generally characterized by its pungent smell, often described as rotten fish. This quality makes it relatively easy to identify in a laboratory setting.

The reaction process can be understood as follows:

• White phosphorus undergoes a series of chemical transformations under basic conditions created by \( \mathrm{NaOH} \)
• During these transformations, phosphorus acts as a reducing agent, eventually leading to the formation of gaseous \( \mathrm{PH}_3 \)

This type of reaction not only aids in understanding phosphine production but also illustrates the active role phosphorus plays in chemical transformations.

Metal and NaOH reactions

Certain metals, like aluminum (Al) and zinc (Zn), react with sodium hydroxide (\( \mathrm{NaOH} \)) to release hydrogen gas (\( \mathrm{H}_2 \)). This transformation occurs particularly under heat, as indicated by the delta symbol (\( \Delta \)).

Here’s a breakdown of what happens:

• In the case of aluminum (\( \mathrm{Al} \)), it reacts with \( \mathrm{NaOH} \) to produce sodium aluminate (\( \mathrm{NaAlO}_2 \)) and hydrogen gas.
• Similarly, zinc (\( \mathrm{Zn} \)) combines with \( \mathrm{NaOH} \) resulting in sodium zincate (\( \mathrm{Na}_2\mathrm{ZnO}_2 \)) and hydrogen gas.

These reactions are notable because they release hydrogen gas, which is a colorless and odorless gas that can be identified by its rapid bubbling and zero smell.

The fundamental chemical properties involved here highlight both the practicality of producing hydrogen and the reactive nature of metals with strong bases.

Gaseous product identification

Identifying gaseous products in chemical reactions is crucial for understanding the nature and applications of those reactions. In metals reacting with \( \mathrm{NaOH} \), hydrogen gas (\( \mathrm{H}_2 \)) is often the outcome. With phosphorus reactions, phosphine (\( \mathrm{PH}_3 \)) is the gas released.

Here’s how you can identify these gases:

• Hydrogen gas is characterized by its lack of smell, along with its flammability. When a burning splint is introduced to hydrogen gas, it will produce a "pop" sound.
• Phosphine, conversely, has a distinct, pungent odor reminiscent of fish, and is less often encountered.

Understanding these differences is vital when conducting experiments, as it helps in safely verifying and utilizing the products of chemical reactions.

These identification methods not only ensure safety within the lab but also enhance comprehension of gaseous products in various chemical processes.