Problem 97 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is formed when mercurous nitrate reacts with \(\mathrm{NaCl}\) ? (a) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Hg}\left(\mathrm{Na}_{2}\right) \mathrm{Cl}\) (c) \(\mathrm{HgCl}_{2}\) (d) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

The product formed is \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\), option (d).

Step 1: Write the Reactants

The reactants in this chemical reaction are mercurous nitrate, \( \text{Hg}_2(\text{NO}_3)_2 \), and sodium chloride, \( \text{NaCl} \).

Step 2: Determine Possible Products

When mercurous nitrate \((\text{Hg}_2(\text{NO}_3)_2)\) reacts with sodium chloride \((\text{NaCl})\), one possible product is a mercury chlorides, like \(\text{Hg}_2\text{Cl}_2\). Another product is likely to be sodium nitrate \((\text{NaNO}_3)\).

Step 3: Write the Balanced Equation

The balanced chemical equation is:\[ \text{Hg}_2(\text{NO}_3)_2 + 2\text{NaCl} \rightarrow \text{Hg}_2\text{Cl}_2 + 2\text{NaNO}_3 \]This equation shows that one mole of mercurous nitrate reacts with two moles of sodium chloride to produce one mole of mercurous chloride \((\text{Hg}_2\text{Cl}_2)\) and two moles of sodium nitrate.

Step 4: Analyze the Choices

Based on the products from the balanced equation, \(\text{Hg}_2\text{Cl}_2\) is formed, which corresponds to option (d). The other options do not match the product of this reaction.

Key Concepts

Understanding Mercurous Nitrate

Mercurous nitrate is a chemical compound, usually appearing as a colorless or white crystalline solid. Its chemical formula is \( \text{Hg}_2(\text{NO}_3)_2 \). In this compound, mercury is in the +1 oxidation state, which is somewhat unique compared to other mercury compounds.

Here are a few key points about mercurous nitrate:

• It is commonly used in various chemical reactions and compounds preparation.
• Due to its mercurial content, it has specific handling and disposal requirements to prevent environmental contamination.
• Reacting it with certain agents, like sodium chloride, can lead to the formation of other mercury compounds, such as mercurous chloride.

Understanding the properties and behavior of mercurous nitrate is crucial for predicting the outcomes of its reactions.

The Role of Sodium Chloride

Sodium chloride, commonly known as salt, has the chemical formula \(\text{NaCl}\). It is among the most familiar chemical compounds, essential in many chemical reactions and processes in nature and industry.

Some important aspects of sodium chloride include:

• It is a key reactant in many neutralization and precipitation reactions, including those involving mercury compounds.
• In reactions, such as with mercurous nitrate, sodium chloride helps to form new compounds by exchanging ions.
• This process often results in a precipitate, highlighting the vital role of sodium chloride as a participant in numerous chemical transformations.

With its ubiquitous presence and efficiency in reactions, sodium chloride remains a fundamental compound in chemistry.

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry, ensuring that matter is conserved throughout a reaction. This process involves making sure that the number of atoms for each element is the same on both sides of the equation.

Here's a simple approach to balancing equations:

• Write down the unbalanced equation with all reactants and products.
• Count the number of atoms of each element present in both reactants and products.
• Adjust coefficients to balance each element one at a time, beginning with the most complex molecule.
• Check to ensure that all atoms balance and that you have the simplest set of coefficients.

For example, in the reaction between mercurous nitrate and sodium chloride, the balanced equation: \[ \text{Hg}_2(\text{NO}_3)_2 + 2\text{NaCl} \rightarrow \text{Hg}_2\text{Cl}_2 + 2\text{NaNO}_3 \] shows that one unit of mercurous nitrate and two units of sodium chloride produce one unit of mercurous chloride and two units of sodium nitrate. Balancing ensures that chemical equations accurately reflect the conservation of mass.

Formation of Mercurous Chloride

Mercurous chloride, with the formula \(\text{Hg}_2\text{Cl}_2\), is commonly known as calomel. It is a grayish-white powder and is used in various applications, from electrochemistry to historical medicinal uses.

Key characteristics of mercurous chloride include:

• It is insoluble in water and often appears as a precipitate in reactions.
• Historically, it was used in medicine, but now its application is limited due to mercury's toxic effects.
• In chemistry, mercurous chloride is an example of a complex mercury compound featuring a +1 oxidation state.

The formation of mercurous chloride in our reaction highlights a fundamental aspect of chemical reactions: the creation of a new substance through the combination and rearrangement of atoms from the reactants.