Problem 6 - A Complete Resource Book in Chemistry for JEE Main

Question

In liquid \(\mathrm{CCl}_{4}\) which of the following has maximum solubility? (a) \(\mathrm{I}_{2}\) (b) \(\mathrm{Br}_{2}\) (c) \(\mathrm{NaCl}\) (d) \(\mathrm{Cl}_{2}^{-}\)

Step-by-Step Solution

Answer

The substance with maximum solubility in CCl_4 is I_2.

Step 1: Understanding Solubility Concepts

In this exercise, we're asked to determine which substance has the maximum solubility in carbon tetrachloride (CCl_4). To solve this, we need to consider the nature of CCl_4 as a non-polar solvent, which typically dissolves non-polar solutes more effectively than polar or ionic solutes.

Step 2: Classify the Options

Let's classify the solubility type of each option: 1. I_2 (Iodine) is non-polar due to its homonuclear diatomic structure. 2. Br_2 (Bromine) is also non-polar for the same reason. 3. NaCl (Sodium chloride) is highly ionic. 4. Cl_2^- (chlorine ion) is an ionic species (hypothetical here as typically incorrect notation for a free anion in solution without a counter-cation).

Step 3: Apply 'Like Dissolves Like' Principle

Non-polar solvents like CCl_4 are most effective at dissolving non-polar substances due to similar attractive forces. Therefore, we expect non-polar substances such as I_2 and Br_2 to be more soluble in CCl_4 than ionic ones like NaCl and Cl_2^-.

Step 4: Compare Non-polar Solutes

Among the non-polar options I_2 and Br_2, I_2 has a larger atomic size compared to Br_2. This results in stronger London dispersion forces in I_2, making it slightly more soluble in CCl_4.

Step 5: Conclusion

Therefore, the substance with the maximum solubility in liquid CCl_4 is I_2 due to it being a non-polar molecule with strong dispersion forces.

Key Concepts

Non-Polar Solvents

Non-polar solvents are chemical compounds that lack a significant difference in electronegativity between their atoms, leading to molecules that do not have a net electric charge. Carbon tetrachloride ( CCl_4 ) is an excellent example of a non-polar solvent. This chemical is often used to dissolve non-polar substances. Non-polar molecules share electrons equally between their atoms, resulting in a balanced structure that doesn't interact well with ions or polar substances.
Common characteristics of non-polar solvents include:

• A symmetric molecular structure that prevents the formation of partial charges.
• Being composed of similar or identical atoms, such as chlorine atoms in CCl_4 .
• Interaction through Van der Waals forces rather than ionic or hydrogen bonds.

Due to these properties, non-polar solvents effectively dissolve other non-polar substances. This is because similar forces between solvent and solute molecules overshadow those with polar molecules or ions.

Like Dissolves Like Principle

The 'Like Dissolves Like' Principle is a guiding concept in chemistry which suggests that polar solvents typically dissolve polar solutes, whereas non-polar solvents dissolve non-polar solutes. It is based on the type of intermolecular forces present. Every molecule experiences forces between its particles, such as Van der Waals forces for non-polar molecules and dipole-dipole interactions for polar molecules.
This principle helps predict solubility and is a useful rule of thumb:

• Polar solvents dissolve ionic or polar substances because of dipole interactions binding the substances together.
• Non-polar solvents dissolve non-polar substances as they do not disturb each other's electron clouds significantly.

Applying this principle to carbon tetrachloride ( CCl_4 ), we recognize it will easily dissolve non-polar substances such as iodine ( I_2 ) and bromine ( Br_2 ), but not ionic compounds like sodium chloride ( NaCl ). This is crucial in solving solubility problems.

London Dispersion Forces

London dispersion forces, also known simply as dispersion forces, are a type of weak intermolecular force that arises from temporary fluctuations in electron density within molecules. These forces occur between all atoms and molecules but are particularly significant in non-polar substances. They become more pronounced with larger and more electron-rich molecules, leading to greater inducement of these temporary attractions.
Key characteristics of London dispersion forces include:

• They increase with the size of the molecules involved, as larger atoms or molecules have more electrons that can shift temporarily.
• They are the predominant force keeping non-polar molecules together, such as in iodine ( I_2 ).
• Being weak relative to stronger bonds like hydrogen or ionic bonds yet crucially important for solubility in non-polar solvents.

In the case of CCl_4 , iodine ( I_2 ) experiences significant London dispersion forces due to its large atomic size, contributing to its high solubility. This concept is pivotal when evaluating which substances dissolve better in non-polar solvents.