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, as it is a nonpolar molecule and adheres to the 'like dissolves like' principle.

Step-by-step solution

Identifying the Polarity of each Solvent

First, we'll assess the polarity of each given solvent. Polarity is determined by the electronegativity difference between the atoms within the molecule and the molecular geometry. 1. Acetone: It has a central carbonyl group (C=O) with a significant electronegativity difference between carbon and oxygen, making it a polar molecule. 2. Methanol: It has an alcohol group (OH) which is polar due to the electronegativity difference between oxygen and hydrogen. 3. Toluene: It consists of a methyl group (CH3) attached to a benzene ring. The benzene ring is composed of carbon and hydrogen atoms, which have similar electronegativities. Thus, toluene is considered a nonpolar molecule. 4. Water: Water is a polar molecule due to the presence of electronegative oxygen bound to hydrogen atoms.

Applying the 'Like Dissolves Like' Principle

According to the 'like dissolves like' principle, nonpolar solutes will dissolve best in nonpolar solvents. Hence, out of the given solvents, toluene is the best solvent for nonpolar solutes, as it is nonpolar.

Key concepts

Nonpolar Solvents

In chemistry, solvents are categorized into two broad types based on their polarity: polar and nonpolar. Nonpolar solvents have molecules that distribute charge equally, resulting in no regions with distinct positive or negative charges. Because of this, they do not mix well with polar substances like water. Instead, nonpolar solvents are great for dissolving other nonpolar compounds.
A key example from the exercise is toluene. Toluene is nonpolar because it primarily consists of carbon and hydrogen atoms, which share electrons evenly, creating a balanced charge distribution. This is why toluene is the best option for dissolving nonpolar solutes in the exercise, since they have similar polarity profiles.

• Nonpolar solvents are not effective with polar solutes due to their charge distribution.
• They work best with substances that have similar electron-sharing and distribution characteristics.

Like Dissolves Like Principle

The 'Like Dissolves Like' principle is a simple rule of thumb used in chemistry to predict solubility. This principle states that solvents will best dissolve solutes with similar polarity. It means polar solvents will dissolve polar solutes, and nonpolar solvents will dissolve nonpolar solutes.
This concept relies on the compatibility of intermolecular forces between substances. In our exercise, toluene, a nonpolar solvent, is ideal for nonpolar solutes because their molecules have similar charge properties, leading to efficient mixing.

• Polarity compatibility is key—similar polarities lead to better dissolving actions.
• It helps predict which solvents will be effective in various chemical reactions.

Understanding this principle is crucial for selecting the right solvent in both laboratory and industrial settings.

Electronegativity

Electronegativity is the ability of an atom to attract shared electrons in a bond. It plays a central role in determining the polarity of molecules. Atoms like oxygen and nitrogen have high electronegativities, meaning they pull electrons towards themselves more strongly, often resulting in polar bonds.
In the exercise, water, acetone, and methanol are polar due to high electronegativity differences within their molecules. For instance, in water, oxygen attracts electrons more than hydrogen, creating a polar molecule. On the contrary, in toluene, carbon and hydrogen atoms have similar electronegativities, resulting in a nonpolar compound.

• A high electronegativity difference typically results in polar molecules.
• Nonpolar molecules usually consist of atoms with similar electronegativity.
• Electronegativity guides the understanding of molecular behavior and interactions.

Recognizing the role of electronegativity aids in predicting molecular reactivity and solubility behavior.