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? Explain.

Short answer

Toluene \(\left(\mathrm{C}_{6} \mathrm{H}_{5}\mathrm{CH}_{3}\right)\) is the best solvent for nonpolar solutes among acetone, methanol, toluene, and water because it is a nonpolar molecule. According to the "like dissolves like" principle, nonpolar solvents dissolve nonpolar solutes, making toluene the most suitable choice in this case.

Step-by-step solution

Understand "Like Dissolves Like" principle

The principle "like dissolves like" helps predict whether a solute will dissolve in a solvent or not. A substance will dissolve in a solvent with similar polarity. In other words, polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes.

Determine the polarity of solvents

We need to analyze the polarity of each solvent to determine whether it is polar or nonpolar: - Acetone \(\left(\mathrm{CH}_{3}\mathrm{COCH}_{3}\right)\): It has a carbonyl group (C=O) and overall symmetry that makes it a polar molecule. - Methanol \(\left(\mathrm{CH}_{3}\mathrm{OH}\right)\): It has an alcohol group (OH) which is highly polar, making the entire molecule polar. - Toluene \(\left(\mathrm{C}_{6} \mathrm{H}_{5}\mathrm{CH}_{3}\right)\): It has an aromatic ring paired with a nonpolar methyl group (CH3). Due to the presence of this nonpolar group, toluene is considered nonpolar. - Water (H2O): It has a bent molecular structure with two polar O-H bonds, making it a highly polar molecule.

Choose the best solvent for nonpolar solutes

From the analysis, we know that toluene is nonpolar while the other three solvents (acetone, methanol, and water) are polar. According to the "like dissolves like" principle, toluene will be the best solvent for nonpolar solutes.

Key concepts

Like Dissolves Like Principle

The concept of the "like dissolves like" principle is a fundamental rule in chemistry. It simply states that solvents tend to dissolve solutes that have similar polarity characteristics.
This means polar solutes are best dissolved in polar solvents, whereas nonpolar solutes will more effectively dissolve in nonpolar solvents.
Polar solvents such as water and alcohols have specific regions of positive and negative charge distribution due to their molecular structure. In contrast, nonpolar solvents like hexane or toluene have a more even distribution of electrons, leading to little or no areas of charge.
When thinking about solubility, always consider the polarity of both the solvent and the solute. This rule of thumb makes it easier to predict the solubility outcomes in various chemical processes.

Nonpolar Solutes

Nonpolar solutes are compounds that do not have distinct positive or negative poles within their molecular structure.
These can include substances such as oils, fats, and many organic molecules that consist mainly of hydrogens and carbons. The absence of charges on nonpolar solutes means they won't mix well with polar solvents that rely on charge interactions to dissolve solutes.
Nonpolar solutes typically dissolve in nonpolar solvents because they undergo dispersion forces, which are weak intermolecular forces that occur between nonpolar molecules.

• Common nonpolar solutes include: saturated hydrocarbons, some aromatic compounds, and nonpolar organometallics.

Understanding whether a solute is polar or nonpolar is crucial for choosing a compatible solvent in laboratory settings.

Laboratory Solvents

In a laboratory setting, choosing the right solvent is critical for the success of chemical reactions and analyses. Solvents are categorized based on their polarity and are selected to match the solutes they need to dissolve.

• Acetone: A common polar solvent used for cleaning laboratory glassware and dissolving polar compounds such as plastics and resins.
• Methanol: Another polar solvent, used in a variety of organic syntheses and as antifreeze due to its ability to lower the freezing point of water.
• Water: Known as the "universal solvent" due to its ability to dissolve many polar substances.
• Toluene: Favored for dissolving paints and certain nonpolar materials due to its nonpolar characteristics.

Recognizing the polarity of each solvent is essential to anticipate their interaction with various solutes. For example, toluene, being nonpolar, is the best choice for dissolving nonpolar solutes. Proper selection of solvents ensures efficient reactions and processes in the lab.