Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

The products formed when heavy water reacts with magnesium nitride, are \(\ldots .\) (a) \(\mathrm{ND}_{3}, \mathrm{Mg}(\mathrm{OD})_{2}\) (b) \(\mathrm{ND}_{3}, \mathrm{Mg}(\mathrm{OH})_{2}\) (c) \(\mathrm{NH}_{3}, \mathrm{Mg}(\mathrm{OH})_{2}\) (d) \(\mathrm{NH}_{3}, \mathrm{Mg}(\mathrm{OD})_{2}\)

Step-by-Step Solution

Answer

The products are ND₃ and Mg(OD)₂, matching option (a).

Step 1: Understand the Reactants

Heavy water is denoted as \( \mathrm{D}_{2}\mathrm{O} \). It is similar to regular water (\( \mathrm{H}_{2}\mathrm{O} \)) but contains deuterium instead of hydrogen. Magnesium nitride is represented as \( \mathrm{Mg}_3\mathrm{N}_2 \). Our task is to identify the products formed when these substances react.

Step 2: Identify the Chemical Reaction

The reaction between magnesium nitride and heavy water can be written as:\[ \mathrm{Mg}_3\mathrm{N}_2 + 6\mathrm{D}_2\mathrm{O} \rightarrow 3\mathrm{Mg(OD)}_2 + 2\mathrm{ND}_3 \].This equation shows that the reaction produces magnesium deuteroxide (\( \mathrm{Mg(OD)}_{2} \)) and deuterated ammonia (\( \mathrm{ND}_{3} \)).

Step 3: Verify the Balanced Equation

To verify the equation is balanced, count the atoms of each element on both sides. For the reactant side: 3 magnesium (Mg), 2 nitrogen (N), 12 deuterium (D), 6 oxygen (O). On the product side: 3 Mg, 2 N, 12 D, 6 O. Both sides have equal atoms of each element, confirming the equation is balanced.

Step 4: Match with Given Options

From the balanced chemical reaction, the products are \( \mathrm{ND}_{3} \) and \( \mathrm{Mg(OD)}_{2} \). Checking the options, we find that this matches option (a): \( \mathrm{ND}_{3}, \mathrm{Mg(OD)}_{2} \).

Key Concepts

Heavy Water Chemistry

Heavy water is a fascinating alternative form of water. It has a unique chemical composition where deuterium, a heavier isotope of hydrogen, replaces the regular hydrogen atoms.
You might wonder why it's called heavy water. The reason is simple: deuterium's added neutron makes it denser than regular water. Its chemical symbol is denoted as \( \mathrm{D}_{2}\mathrm{O} \), as opposed to regular water, which is \( \mathrm{H}_{2}\mathrm{O} \).
Physically, heavy water looks and behaves very similarly to regular water. However, its properties in chemical reactions often differ, due to the presence of deuterium.
Due to these differences, heavy water is used in nuclear reactors and scientific research to study isotopic effects. It can also replace regular water in certain chemical reactions to produce isotopically labeled compounds. This property is especially helpful in tracing processes in biological systems or conducting experiments requiring precise tracking of chemical fate.

Magnesium Nitride Reactions

Magnesium nitride, denoted as \( \mathrm{Mg}_3\mathrm{N}_2 \), is a compound formed by magnesium and nitrogen. It is known for its reactivity with water, producing ammonia and magnesium hydroxide.
When magnesium nitride reacts with heavy water, this typical reaction converts, due to the deuterium substituting for hydrogen. This alters the products formed.
The general reaction can be expressed as:

• \( \mathrm{Mg}_3\mathrm{N}_2 + 6\mathrm{D}_2\mathrm{O} \rightarrow 3\mathrm{Mg(OD)}_2 + 2\mathrm{ND}_3 \)

As seen here, magnesium nitride reacts with \( \mathrm{D}_2\mathrm{O} \) to form magnesium deuteroxide \( \mathrm{Mg(OD)}_2 \) and deuterated ammonia \( \mathrm{ND}_3 \).
This reaction illustrates a practical application of magnesium nitride's reactivity, adjusted for isotopic variations. It's a crucial example of how changing a simple component like the hydrogen isotope can significantly affect chemical processes and the resulting compounds.

Balanced Chemical Equations

Balanced chemical equations are essential for accurately representing chemical reactions. They reflect the principle of the conservation of mass, meaning the total mass of reactants equals the total mass of products.
To balance an equation, both the reactant and product sides must have the same number of each type of atom. For the reaction of heavy water with magnesium nitride:

• Reactants: 3 magnesium (Mg), 2 nitrogen (N), 12 deuterium (D), and 6 oxygen (O)
• Products: 3 \( \mathrm{Mg(OD)}_2 \) (providing 3 Mg, 6 D, and 6 O) and 2 \( \mathrm{ND}_3 \) (providing 2 N and 6 D)

By counting and comparing these atoms, we can confirm the equation is balanced.
It's vital to achieve this balance to ensure the equation accurately represents the chemical reaction occurring. Understanding how to balance equations is a fundamental skill in chemistry, supporting everything from simple laboratory reactions to complex industrial processes.