Problem 42 - A Complete Resource Book in Chemistry for JEE Main

Question

In the reaction \(\mathrm{Zn}+\mathrm{NaOH} \longrightarrow \Delta \longrightarrow\), the product \(\mathrm{A}\) is (a) \(\mathrm{Zn}(\mathrm{OH})_{2}\) (b) \(2 \mathrm{NaZnO}_{2}\) (c) \(\mathrm{Na}_{2} \mathrm{ZnO}_{2}\) (d) none of these

Step-by-Step Solution

Answer

The product \(A\) is \(\mathrm{Na}_{2}\mathrm{ZnO}_{2}\), answer (c).

Step 1: Understanding the Reaction Context

Zinc reacts with sodium hydroxide (NaOH) under heat (denoted by \(\Delta\)) to form a product. In this reaction, zinc behaves as an amphoteric element, which means it can react with both acids and bases. Here, zinc will react with NaOH to produce a zincate compound.

Step 2: Identifying Potential Products

When zinc reacts with sodium hydroxide, it forms sodium zincate. Sodium zincate exists in the form \(\mathrm{Na}_{2} \mathrm{ZnO}_{2}\). This gives us the compound commonly seen in such reactions involving zinc and a strong base like NaOH.

Step 3: Comparing Against Given Options

From the potential products, we learned that the likely product is \(\mathrm{Na}_{2} \mathrm{ZnO}_{2}\). Now we compare it to the given options. The correct option is (c) \(\mathrm{Na}_{2} \mathrm{ZnO}_{2}\) which matches our identified compound.

Key Concepts

Zinc oxide formation

The transformation of zinc into zinc oxide is an important process that involves heat and sometimes additional substances. Zinc oxide (ZnO) is an amphoteric oxide, meaning it can react with both acids and bases.

When zinc is heated in the presence of oxygen, zinc oxide forms as a result of the chemical reaction: \[ \text{2Zn} + \text{O}_2 \rightarrow \text{2ZnO} \]A white powdery substance, zinc oxide is well-known for its applications in ceramics, medicine, and sunscreens due to its reflective and protective properties.

Additionally, zinc oxide formation can occur in the presence of other chemical reactions, such as when it reacts with sodium hydroxide. This reaction highlights zinc's amphoteric nature and opens doors to numerous chemical possibilities.

Sodium zincate

Sodium zincate is a fascinating result of the reaction between zinc and sodium hydroxide. In chemical contexts involving strong bases, zinc tends to form zincates, which are derivatives containing the zincate ion.

• Formed when zinc reacts with a strong base, such as NaOH, under heat.
• The general reaction involves the formation of sodium zincate and hydrogen gas:

\[ \text{Zn} + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow \text{Na}_2\text{ZnO}_2 + 3\text{H}_2 \] Sodium zincate (Na_2ZnO_2) can serve as a precursor in the synthesis of other zinc compounds and helps in understanding the amphoteric behavior of zinc.

It also displays versatility in industrial applications, especially in industries that require the deposition of zinc compounds onto surfaces.

Chemical reactions with NaOH

Understanding chemical reactions with sodium hydroxide ( NaOH ) is essential in grasping the behavior of compounds like zinc. Sodium hydroxide is a strong alkali, capable of breaking down organic and inorganic materials.

In the context of reactions with metals, NaOH tends to react with those that are amphoteric, like zinc. Here’s what occurs:

• Zinc reacts with NaOH, as outlined in the previous section, forming sodium zincate and highlighting zinc’s dual ability to engage with both acids and bases.
• This reaction is crucial in industries such as electroplating and manufacturing.

Sodium hydroxide interactions often result in precipitations or solutions that facilitate further chemical processes. Moreover, NaOH as a reactant in chemical equations helps illustrate the broader concept of base-metal reactions and the funneled outcomes they produce when combined with amphoteric metals like zinc.