Question

Ethyl ether, \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}\), is \(7 \%\) miscible in water. Explain why ether is only partially miscible even though molecules contain an electronegative oxygen atom.

Short answer

Ether's partial miscibility in water is due to its larger non-polar hydrocarbon chain, which limits mixing despite its polar oxygen atom.

Step-by-step solution

Understanding Ether's Structure

Ethyl ether (C₄H₁₀O) consists of a saturated hydrocarbon chain (four carbon atoms and ten hydrogen atoms) and an electronegative oxygen atom. This structure has two distinct parts: a hydrophobic hydrocarbon chain and a polar oxygen atom, which contributes to ether's partial miscibility in water.

Identifying Polar and Non-Polar Aspects

The presence of the electronegative oxygen atom imparts a polar character to ether, which typically encourages interaction with water because water is also polar. In contrast, the majority of the ethyl ether molecule consists of a non-polar hydrocarbon chain, which does not interact well with water, as water generally does not mix well with non-polar substances.

Analyzing Solubility Behavior

The solubility of a substance in water depends on the balance between the polar and non-polar characteristics of the molecule. As the polar influence of the oxygen atom in ether is overshadowed by the larger non-polar hydrocarbon chain, ether is only partially miscible in water. Thus, only a small percentage (7%) is miscible.

Concluding the Explanation

Ether is only partially miscible in water due to its mixed molecular characteristics. Although the oxygen atom facilitates partial mixing, the larger non-polar hydrocarbon chain limits the extent of miscibility, as it does not effectively interact with the polar nature of water.

Key concepts

Hydrophobic Hydrocarbon Chain

In chemistry, hydrophobic hydrocarbon chains play a critical role in determining the properties of a molecule, especially its interaction with water. A hydrocarbon chain consists primarily of carbon and hydrogen atoms linked by covalent bonds, forming a structure that is non-polar. This non-polar nature means that these chains do not readily form hydrogen bonds with water molecules.
Hydrocarbons, being non-polar, tend to repel water, classifying them as hydrophobic. The term "hydrophobic" literally means "water-fearing."
When integrated into a molecule like ethyl ether, these chains can significantly influence the molecule's overall behavior and solubility in polar solvents like water:

• Hydrophobic chains avoid interaction with water, leading to limited solubility.
• This lack of interaction is due to an imbalance in energy: water would rather interact with itself than with non-polar substances.

The dominance of a non-polar hydrocarbon chain in ethyl ether means that, despite the presence of a polar oxygen atom, much of the ether molecule remains water-insoluble.

Polar Non-Polar Interaction

The interaction between polar and non-polar components within a molecule affects its behavior in solvents. Polar molecules, like water, have regions of positive and negative charge. They tend to interact well with other polar substances, forming hydrogen bonds.
In contrast, non-polar substances lack this charge separation, making it difficult for them to interact with polar compounds. For ethyl ether, the molecule consists of a polar region (the oxygen atom) and a substantially larger non-polar region (the hydrocarbon chain):

• The polar oxygen atom can attract water molecules due to its electronegative nature.
• However, the non-polar hydrocarbon chain does not interact with water, reducing overall miscibility.
• This results in only partial miscibility because the polar interactions are overshadowed by the predominance of non-polar character.

Such contrasting interactions within a single molecule lead to partial miscibility, as seen with ethyl ether's limited solubility of 7% in water.

Solubility Behavior

Solubility behavior in molecular chemistry revolves around the "like dissolves like" principle, where polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes. Ethyl ether's partial miscibility in water demonstrates an important aspect of solubility behavior in mixed-character molecules.
Although ethyl ether contains an electronegative oxygen contributing to its polar nature, the molecule's bulk is comprised of a non-polar hydrocarbon chain. The balance between these polar and non-polar elements influences solubility:

• Polar solvents like water interact well with the polar sections of a molecule.
• However, larger non-polar areas can inhibit these interactions, reducing solubility.
• In ethyl ether, about 7% of the molecule can interact with water, explained by the dominating non-polar chain limiting miscibility.

Understanding these principles is essential to predicting the behavior of complex molecules in different solvents, highlighting why ethyl ether is only somewhat soluble in water.