The volume of mixing \((\Delta V)\) is not zero for which of the following solutions?

Ethanol and Acetone

The correct answer is option 3. Ethanol and Acetone.

To understand which solution exhibits a non-zero volume of mixing (\(\Delta V\)), it's important to delve into how mixing affects the volume based on the intermolecular interactions between the components. Here's a detailed explanation for each pair of solutions.

1. Chloroethane and Bromoethane

Chemical Nature: Both chloroethane (\(C_2H_5Cl\)) and bromoethane (\(C_2H_5Br\)) are haloalkanes, and they are structurally similar.

Intermolecular Forces: Both substances interact through dispersion forces (Van der Waals forces). Since these molecules are similar in nature and size, their intermolecular interactions are also similar.

Mixing Behavior: When similar molecules mix, the intermolecular forces do not change drastically, resulting in minimal or negligible volume change. The volume of mixing (\(\Delta V\)) for such solutions is typically close to zero.

2. Benzene and Toluene

Chemical Nature: Benzene (\(C_6H_6\)) and toluene (\(C_6H_5CH_3\)) are both aromatic hydrocarbons with very similar structures.

Intermolecular Forces: Both substances interact through dispersion forces and have similar types of intermolecular forces.

Mixing Behavior: Similar aromatic hydrocarbons mix nearly ideally, meaning the volume of mixing is close to zero. There are no significant interactions that lead to a large change in volume.

3. Ethanol and Acetone

Chemical Nature: Ethanol (\(C_2H_5OH\)) is an alcohol with a hydroxyl group that can form hydrogen bonds, while acetone (\((CH_3)_2CO\)) is a ketone with dipole-dipole interactions.

Intermolecular Forces: Ethanol can form hydrogen bonds with itself, which are strong compared to dipole-dipole interactions in acetone.

Mixing Behavior: When ethanol and acetone are mixed, the hydrogen bonds between ethanol molecules interact with the dipole forces of acetone. This can lead to a more complex interaction where the molecules fit together more efficiently, causing a change in volume. Generally, this results in a decrease in volume due to the formation of strong hydrogen bonds between ethanol and acetone. The volume of mixing is often non-zero due to these interactions.

4. n-Hexane and n-Heptane

Chemical Nature: n-Hexane (\(C_6H_{14}\)) and n-Heptane (\(C_7H_{16}\)) are both straight-chain alkanes.

Intermolecular Forces: They interact through dispersion forces, which are weak and similar in nature.

Mixing Behavior: Since n-hexane and n-heptane have similar structures and intermolecular forces, their mixing typically results in minimal volume change. The volume of mixing for such similar non-polar substances is close to zero.

Summary of Volume of Mixing:

Volume of Mixing Close to Zero:

Chloroethane and Bromoethane: Similar molecules with weak Van der Waals forces.

Benzene and Toluene: Similar aromatic hydrocarbons with Van der Waals forces.

n-Hexane and n-Heptane: Similar alkanes with Van der Waals forces.

Non-Zero Volume of Mixing:

Ethanol and Acetone: Different types of intermolecular forces (hydrogen bonding in ethanol and dipole-dipole interactions in acetone) can lead to significant changes in volume when mixed.

Conclusion:

Ethanol and acetone exhibit a non-zero volume of mixing due to the interaction between different types of intermolecular forces, which can result in either a decrease or increase in volume depending on how well the molecules fit together.