Problem 64 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is insoluble in water? (a) \(\mathrm{CaF}_{2}\) (b) \(\mathrm{NaCl}\) (c) \(\mathrm{HgCl}_{2}\) (d) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

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Step 1: Understand the question

The question asks us to find which one of the given compounds does not dissolve in water, which is termed as insoluble.

Step 2: Analyze each compound

We need to determine the solubility of each compound in water by referring to common solubility rules.

Step 3: Solubility of Calcium Fluoride ( 20O)] o)] ^2}bind calcium ions produceoative bonds.forming 20O] o)] ^2} . help Calcium Fluoride ( 20O)] (O)] is generally considered insoluble in water due to its low solubility.

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Step 4: Solubility of Sodium Chloride ( 20O)]

Sodium chloride is known as common table salt and is highly soluble in water.

Step 5: Solubility of Mercury(II) Chloride ( 20O)]

Mercury(II) chloride ( 20O oroscopic{=]5 holog {Br+c HB, chloride 20O)hrl C0wr+ tea(C and sP0WR e{}ty

Key Concepts

Insoluble Compounds

In chemistry, solubility refers to how well a substance can dissolve in a solvent, such as water. When a compound is labeled as insoluble, it means it does not dissolve well in water, or only dissolves to a very small extent. This happens because the forces holding the solid together are stronger than the forces that water can exert to pull the particles apart.

For example, calcium fluoride (\(\mathrm{CaF}_{2}\)) is considered an insoluble compound in water. In the case of \(\mathrm{CaF}_{2}\), strong ionic bonds between calcium and fluoride ions contribute to its insolubility. The lattice structure of \(\mathrm{CaF}_{2}\) is difficult for water molecules to break apart, leading to its low solubility.

This concept is vital for predicting whether a compound will dissolve in water, which can affect its usefulness in various chemical reactions.

Solubility Rules

Solubility rules are guidelines to help predict whether an ionic compound is soluble or insoluble in water. By consulting these rules, it becomes easier to forecast the behavior of compounds in aqueous solutions.

Some general solubility rules include:

• Most nitrate (\(\mathrm{NO}_{3}^{-}\)) salts are soluble.
• Most salts containing alkali metal ions (like \(\mathrm{Na}^{+}\) or \(\mathrm{K}^{+}\)) and ammonium (\(\mathrm{NH}_{4}^{+}\)) are soluble.
• Chlorides, bromides, and iodides are soluble, except for salts with silver, lead, and mercury.
• Sulfates are generally soluble, with exceptions like barium sulfate and calcium sulfate being only sparingly soluble.

By using these rules, students can quickly determine the solubility of compounds without needing to experiment directly. For instance, \(\mathrm{NaCl}\) is highly soluble, as sodium is an alkali metal ion. However, \(\mathrm{HgCl}_{2}\), despite being a chloride, is not as soluble due to the presence of mercury.

Water Solubility

Water solubility is a measure of how much of a substance can dissolve in water at a given temperature. It plays a crucial role in both natural processes and industrial applications. A substance is typically described as soluble if it dissolves significantly, and as insoluble if it remains mostly undissolved.

A compound's solubility in water depends on various factors:

• Temperature: Generally, solubility increases with temperature for solids.
• Nature of Solvent and Solute: Polar solutes tend to dissolve well in polar solvents like water.
• Ionic Strength: Compounds composed of oppositely charged ions may dissolve due to interaction with water molecules.

For instance, compounds such as \(\mathrm{NaCl}\) readily dissolve in water due to the ionic nature and the ability of water molecules to stabilize these ions in solution. Understanding water solubility is essential for predicting the behavior of substances in biological systems, environmental settings, and chemical processes.