Problem 14 - Chemistry and Chemical Reactivity

Question

Acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3},\) is quite soluble in water. Explain why this should be so. (EQUATION CANNOT COPY)

Step-by-Step Solution

Answer

Acetone is soluble in water due to their similar polarities, allowing for dipole interactions and hydrogen bonding.

Step 1: Identify Intermolecular Forces

Acetone (\(\mathrm{CH}_{3}\mathrm{COCH}_{3}\)) and water are both polar molecules. Acetone features a carbon-oxygen double bond, known as a carbonyl group, which introduces a dipole moment due to the significant difference in electronegativity between carbon and oxygen. Water, on the other hand, has a bent molecular shape with a polar covalent bond, resulting in a strong dipole as well.

Step 2: Assess Acetone and Water Interactions

Considering the polar nature of both acetone and water, they can engage in dipole-dipole interactions. Acetone's oxygen atom can hydrogen bond with the hydrogen atoms of water molecules because of water's lattice of hydrogen bonds, although water's nature is more suitable for hydrogen bonds due to its own intramolecular bonding.

Step 3: Analyze the Solubility

Solubility often arises when solvent and solute share similar polarities. The polarities of both acetone and water lead them to form hydrogen bonds readily between the hydrogen atoms of water and the oxygen atom of acetone. This results in a strong mutual attraction that makes acetone quite soluble in water.

Key Concepts

Dipole-Dipole Interactions

Dipole-dipole interactions occur between polar molecules, where positive and negative charges attract each other. Consider acetone, which has a carbonyl group. The double bond between carbon and oxygen creates a dipole moment, as oxygen is more electronegative than carbon. This causes a partial negative charge on oxygen and a partial positive charge on carbon. As a result, acetone molecules have regions of positive and negative charge.

Water, being a polar molecule as well, exhibits a similar feature. Its bent shape and electronegativity difference between oxygen and hydrogen result in a strong dipole moment. The negative end of one molecule interacts with the positive end of another. In solutions, such as those involving acetone and water, these dipole-dipole interactions are significant.

They help bring about the dissolution of acetone in water. The forces of attraction between the differently charged ends of water and acetone molecules stabilize the mixture, making the interaction spontaneous.

Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole interaction. It occurs when hydrogen, bonded to an electronegative atom like oxygen or nitrogen, forms a bridge with another electronegative atom. In water, each hydrogen atom can form a hydrogen bond with the oxygen of another water molecule, creating a lattice of interactions. This gives water its unique properties, such as high boiling point and surface tension.

Acetone, although predominantly interacting through dipole-dipole forces, can engage in hydrogen bonding with water. The oxygen in acetone can serve as a hydrogen bond acceptor. This is crucial because when acetone is mixed with water, these bonds lead to stronger interactions between the molecules.

• Hydrogen bonding helps increase the solubility of acetone in water, as water molecules interact tightly with the lone pairs of electrons on acetone's oxygen.
• This attraction facilitates a stable solution where the two types of molecules can mix freely.

Understanding these bonds helps explain why acetone easily dissolves in water compared to nonpolar solvents.

Polarity

Polarity refers to the distribution of electrical charges over the atoms in a molecule. This concept is essential to understanding why two substances, such as acetone and water, can mix well. When a molecule is polar, it has a distinct positive and negative end, which results from an uneven distribution of electrons.

In acetone, the central carbon atom attached to the more electronegative oxygen attracts electrons towards itself, creating a polar molecule. Similarly, water is also polar, with a partial positive charge near the hydrogens and a partial negative charge near the oxygen.

• When polar molecules like acetone and water collide, they align their opposite charges, resulting in interactions that can stabilize the mixture.
• This phenomenon follows the principle "like dissolves like," which indicates that substances with similar polarities tend to be soluble in each other.

Therefore, acetone's ability to dissolve in water is largely due to their polar nature, which allows for conducive interactions and effective mixing.