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

Question

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

Step-by-Step Solution

Answer

The product A is (c) \( \mathrm{Na}_2\mathrm{ZnO}_2 \).

Step 1: Identify the Reactants

The reactants in the given chemical equation are zinc \( \mathrm{Zn} \) and sodium hydroxide \( \mathrm{NaOH} \). It's important to consider the conditions given, such as the presence of heat (\( \Delta \)).

Step 2: Consider the Reaction Conditions

The symbol \( \Delta \) indicates that heat is applied. This could suggest that the reaction might produce a different product under thermal conditions compared to those under normal temperatures.

Step 3: Predict the Products

Zinc reacts with \( \mathrm{NaOH} \) under heat to commonly form sodium zincate \( \mathrm{Na}_2\mathrm{ZnO}_2 \). The reaction can be written as: \[ \mathrm{Zn} + 2\mathrm{NaOH} \xrightarrow{\Delta} \mathrm{Na}_2\mathrm{ZnO}_2 + \mathrm{H}_2 \].

Step 4: Identify the Correct Option

From the predicted product \( \mathrm{Na}_2\mathrm{ZnO}_2 \), compare with the given options. Option (c) matches the predicted reaction product.

Key Concepts

Understanding Thermal Reactions

When we talk about thermal reactions, we are looking at how heat impacts chemical reactions. Heat, represented by the symbol \( \Delta \), plays an integral role in many chemical transformations. It is not just a catalyst that speeds up reactions, but it can also fundamentally change the products that are formed.

• Heat can provide the necessary energy to break chemical bonds within the reactants, leading to new arrangements and formations in the products.
• In the case of some reactions, applying heat might lead to completely different products than what would form at room temperature.
• The reaction between zinc \( \mathrm{Zn} \) and sodium hydroxide \( \mathrm{NaOH} \) is an excellent example. When heat is applied, it leads to the formation of sodium zincate \( \mathrm{Na}_2\mathrm{ZnO}_2 \), which might not be the case at lower temperatures.

Understanding these thermal effects is crucial when predicting the outcome of reactions in both academic and real-world scenarios.

Balancing Chemical Equations

Balancing chemical equations involves ensuring that the number of atoms for each element is the same on both sides of the equation. This concept is rooted in the law of conservation of mass.

• When balancing equations, start by listing all the elements involved in the reaction and count their respective atoms in reactants and products.
• Add coefficients to the reactants or products to make sure the atom count matches on both sides.
• Take the zinc and sodium hydroxide reaction as an example: \( \mathrm{Zn} + 2\mathrm{NaOH} \xrightarrow{\Delta} \mathrm{Na}_2\mathrm{ZnO}_2 + \mathrm{H}_2 \). Here, 2 moles of \( \mathrm{NaOH} \) are necessary to balance the reaction, ensuring the same number of each type of atom appears on both sides.

Balancing chemical equations is an essential skill in chemistry, helping to depict accurately how reactants turn into products.

Reactivity of Metals with Bases

Reactivity involves how substances interact with each other, particularly how metals react with substances like acids or bases. Some metals react with bases, leading to interesting outcomes, like the formation of complex ions or compounds.

• Zinc \( \mathrm{Zn} \) is less reactive with bases at normal temperatures, but under special conditions like heating, it can react significantly, forming products such as sodium zincate \( \mathrm{Na}_2\mathrm{ZnO}_2 \).
• Different metals have varying reactivity levels with bases. Zinc's moderate reactivity means it doesn't react with bases like \( \mathrm{NaOH} \) under normal conditions without additional stimuli such as heat.
• Understanding these interactions is important for practical applications, such as in the production of specific metal compounds or in industrial chemical processes.

By examining the reactivity of metals, students can better grasp why certain reactions occur under specific conditions and how to manipulate those conditions in practical applications.