Question

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3},\) is a common laboratory solvent. It is usually contaminated with water, however. Why does acetone absorb water so readily? Draw molecular structures showing how water and acetone can interact. What intermolecular force(s) is(are) involved in the interaction? (EQUATION CAN'T COPY)

Short answer

Acetone absorbs water due to hydrogen bonding and dipole-dipole interactions between their polar molecules.

Step-by-step solution

Understanding Acetone

Acetone, with the chemical formula \( ext{CH}_3 ext{COCH}_3\), is a polar molecule due to the presence of a carbonyl group (\(\text{-C=O}\)). This structure makes the oxygen atom in acetone have a partial negative charge (\(\delta^-\)), while the carbon atom bonded to oxygen has a partial positive charge (\(\delta^+\)).

Structure of Water

Water (\(\text{H}_2\text{O}\)) is also a polar molecule with oxygen having a partial negative charge and hydrogen atoms having partial positive charges. This polarity allows water to engage in hydrogen bonding, where the hydrogen atoms are attracted to oxygen atoms of neighboring molecules.

Interactions Between Acetone and Water

The polarity of both acetone and water allows them to interact through strong dipole-dipole interactions and hydrogen bonding. Oxygen in acetone can form hydrogen bonds with the hydrogen atoms of a water molecule. The partial positive hydrogen of water is attracted to the partial negative oxygen in acetone.

Drawing Molecular Structures

To illustrate, draw acetone with its \( ext{-C=O}\) group and water with its v-shape. Show the partial charges and draw dotted lines between the hydrogen atoms of water and the oxygen atom of acetone to represent hydrogen bonding. This visual will help understand how hydrogen bonds form between water and acetone.

Conclusion on Intermolecular Forces

The primary intermolecular forces involved in the interaction between acetone and water are hydrogen bonding and dipole-dipole interactions. These forces are strong enough to cause acetone to readily absorb water from its surroundings.

Key concepts

Understanding Acetone

Acetone is a common solvent, recognized by its chemical formula \(\text{CH}_3\text{COCH}_3\). This molecule is marked by its polar nature, mainly due to the presence of the carbonyl group \(\text{-C=O}\). The carbonyl group works as a polarizing element which means it creates partial charges in the molecule. More specifically, the oxygen atom in acetone bears a partial negative charge \(\delta^-\), while the carbon atom, bonded directly to this oxygen, carries a partial positive charge \(\delta^+\).

The distinctiveness of this polarity is crucial for its interactions with other molecules, such as water. Thus, acetone's ability to mix or "absorb" water becomes clear when we consider how the polarity influences intermolecular forces. In essence, this polar nature is what makes acetone an excellent medium for interacting with other polar substances.

Principles of Hydrogen Bonding

Hydrogen bonding is a specialized, yet common type of dipole-dipole attraction. It occurs when hydrogen, bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine, interacts with another electronegative atom possessing lone pairs.

In the case of water \(\text{H}_2\text{O}\), the oxygen atom holds a partial negative charge while the hydrogen atoms have partial positive charges. This setup enables water molecules to engage in hydrogen bonding between each other, creating a network of strong intermolecular attractions that give water its unique properties such as high boiling point and surface tension.


When water forms hydrogen bonds with acetone, the hydrogen's partial positive charge is attracted to the oxygen's partial negative charge in acetone. This connection between molecules illustrates how substances like acetone and water can form temporary bonds, allowing them to stay mixed.

Dipole-Dipole Interactions

Alongside hydrogen bonding, dipole-dipole interactions play a significant role in the interaction between acetone and water. These forces occur between molecules that exhibit permanent dipoles, meaning the charge distribution within the molecule remains consistently offset.

For acetone, which features a permanent dipole thanks to its polar molecular structure, the partial negative charge on the oxygen atom can engage in dipole interactions with positive regions on other molecules, such as the hydrogen atoms of water.
These interactions are crucial because they strengthen the overall molecular connection between acetone and water. They essentially complement hydrogen bonds by providing an additional layer of attraction between the molecules, aiding in their ability to mix and remain in solution together.

In summary, the interplay of hydrogen bonding and dipole-dipole interactions elucidates why acetone is so adept at absorbing water, a concept that enhances our understanding of intermolecular forces in chemical solutions.