Question

Common laboratory solvents include acetone $\left({\mathrm{CH}}_3{\mathrm{COCH}}_3\right)$, methanol $\left({\mathrm{CH}}_3\mathrm{OH}\right)$, toluene $\left({\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_3\right),$ and water. Which of these is the best solvent for nonpolar solutes?

Short answer

Toluene $\left({\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_3\right)$ is the best solvent for nonpolar solutes among the given common laboratory solvents, as it is a nonpolar solvent itself, and "like dissolves like."

Step-by-step solution

Determine the polarity of acetone

Acetone (CH3COCH3) has a carbonyl group (C=O) in the middle of its structure, making the molecule polar. Oxygen is more electronegative than carbon, creating a dipole moment in the carbonyl group, which makes acetone a polar solvent.

Determine the polarity of methanol

Methanol (CH3OH) contains an oxygen-hydrogen (O-H) bond, which is polar due to the high electronegativity difference between oxygen and hydrogen. As a result, methanol is a polar solvent.

Determine the polarity of toluene

Toluene (C6H5CH3) has a benzene ring (C6H5) bonded to a methyl group (CH3). Both the benzene ring and the methyl group are composed of carbon and hydrogen atoms, with very little difference in electronegativity, making toluene a nonpolar solvent.

Determine the polarity of water

Water (H2O) is a well-known polar solvent due to its bent shape and the large difference in electronegativity between oxygen and hydrogen. This results in a dipole moment, making water a polar solvent.

Identify the best solvent for nonpolar solutes

Considering the polarity of each solvent, we can conclude that toluene, being a nonpolar solvent, will be the best choice for dissolving nonpolar solutes among the given common laboratory solvents.

Key concepts

Nonpolar Solute Solubility

In the world of chemistry, when choosing a solvent for dissolving substances, understanding polarity is key – especially with nonpolar solutes. Nonpolar substances typically have molecules that do not have significant differences in electronegativity among their atoms, leading to an even distribution of charge. This lack of polar nature means nonpolar solutes tend to dissolve best in nonpolar solvents.

The principle ">like dissolves like" applies here. Nonpolar solvents can mix seamlessly with nonpolar solutes because both types don’t have any charges or poles. This allows for their molecules to interact without the resistance or interference that arises from polar charges.

Thus, in a laboratory setting, solvents such as toluene, which is nonpolar, are ideal for dissolving nonpolar solutes efficiently.

Carbonyl Group in Acetone

Acetone, a common laboratory solvent, has a structure defined by its carbonyl group (C=O) situated between two methyl groups (CH3). The presence of this carbonyl group is crucial because it imparts polarity to the acetone molecule.

The oxygen in the carbonyl group is more electronegative than the carbon, creating a partial negative charge on the oxygen and a partial positive charge on the carbon. This charge difference leads to what is known as a dipole moment, which directly contributes to acetone's polarity.

This means that acetone is a polar solvent, making it more suited for dissolving polar solutes rather than nonpolar ones. Understanding this property helps chemists choose the right solvent for reactions or processes that require solubility considerations.

Benzene Ring in Toluene

Toluene is a well-known solvent with a unique nonpolar character due in part to its structure, which consists of a benzene ring attached to a methyl group. The benzene ring, ${\text{C}}_6{\text{H}}_5$, is a planar cyclic structure with alternating single and double bonds, promoting electron delocalization.

This electron arrangement in the benzene ring means there are no significant positive or negative poles in the molecule. Additionally, the methyl group (${\text{CH}}_3$) attached to the benzene ring does not contribute any polarity, which further enforces toluene's nature as a nonpolar solvent.

Because of its nonpolar nature, toluene is perfectly suited for dissolving nonpolar solutes, adhering to the rule of ">like dissolves like." Its ability to mix with other nonpolar substances while remaining unreactive makes it valuable in various chemical processes.

Dipole Moment in Water

Water is often described as a "universal solvent" due to its polar nature. The molecule's bent shape, along with the presence of highly electronegative oxygen atoms, results in a significant dipole moment. The oxygen atoms attract electrons more than the hydrogen atoms, causing an uneven distribution of charge that creates polarity.

This inherent dipole moment allows water to dissolve many ionic and polar substances effectively. It establishes hydrogen bonding, which is foundational to water's solvent capabilities. However, despite its strengths in dissolving polar solutes, water is generally unsuitable for nonpolar solutes because the difference in polarities leads to poor solubility.

Understanding water's dipole moment is critical for appreciating why it excels as a solvent for certain types of reactions and mixtures, while falling short for nonpolar substances.