Question

You are doing an experiment in the laboratory and want to prepare a solution in a polar solvent. Which solvent would you choose, methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\) or toluene \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{3}\right) ?\) Explain your choice. EQUATION CANT COPY

Short answer

Choose methanol, as it is a polar solvent.

Step-by-step solution

Understand Polar and Non-polar Solvents

Polar solvents have molecules with a net dipole moment due to differences in electronegativity between bonded atoms. Non-polar solvents have molecules with no or very low net dipole moment.

Determine Polarity of Methanol

Methanol ( ext{CH}_{3} ext{OH}) is a polar solvent. The molecule has a hydroxyl ( ext{-OH}) group, which creates a dipole due to the difference in electronegativity between the oxygen and hydrogen atoms.

Determine Polarity of Toluene

Toluene ( ext{C}_{6} ext{H}_{5} ext{CH}_{3}) is a non-polar solvent. It consists mostly of carbon and hydrogen atoms with similar electronegativities, resulting in a molecule with low overall polarity.

Select the Appropriate Solvent

To select a polar solvent, choose methanol because it has a significant polar hydroxyl group that facilitates dissolving polar substances through hydrogen bonding.

Key concepts

Methanol

Methanol, also known as methyl alcohol, is a simple alcohol with the chemical formula \(\text{CH}_3\text{OH}\). It is known for its distinctive ability to act as a polar solvent, making it suitable for various chemical reactions and processes in the laboratory. Methanol consists of a hydroxyl group \((-\text{OH})\) attached to a methyl group \((\text{CH}_3)\). This hydroxyl group plays a crucial role in defining the molecule's polar nature.

One of the key characteristics of methanol is its polar nature, resulting from the significant electronegativity difference between oxygen and hydrogen atoms in the \(-\text{OH}\) group. This leads to a partial positive charge on hydrogen and a partial negative charge on oxygen, creating a dipole. Because of this polar nature, methanol can dissolve various polar substances efficiently, making it highly versatile in chemical applications.

• Used in organic synthesis.
• Excellent solvent for polar substances.
• Non-toxic in small amounts, but caution is needed in larger doses.

Toluene

Toluene is an aromatic hydrocarbon with the chemical formula \(\text{C}_6\text{H}_5\text{CH}_3\). It is classified as a non-polar solvent and is characterized by its benzene ring structure, which contributes to its chemical stability and inert nature in various industrial applications. Unlike methanol, toluene does not have significant electronegative groups like \(-\text{OH}\), making it less polar. The similar electronegativities of carbon and hydrogen in toluene result in a low dipole moment, reinforcing its non-polar nature.

Due to its non-polar characteristics, toluene is ideal for dissolving non-polar compounds, such as oils, resins, and other hydrocarbons. It is frequently used in industries ranging from paint thinners to glues and in the production of other chemicals.

• Non-polar solvent.
• Good for dissolving non-polar substances.
• Commonly used in industrial settings.

Dipole Moment

A dipole moment is a measure of the separation of positive and negative charges in a molecule. It is an essential concept in understanding the polarity of compounds. Molecules with a high dipole moment typically have regions of partial positive and negative charge, caused by differences in electronegativity between bonded atoms. This results in an overall polarity, allowing these molecules to interact with other polar substances through electrostatic forces.

Methanol, for instance, has a significant dipole moment because of the \(-\text{OH}\) group's electronegativity disparity between the oxygen and hydrogen atoms. This makes it a polar solvent capable of dissolving other polar compounds through these electrostatic interactions. Conversely, toluene lacks such charge separation within the molecule, which results in a very low dipole moment, characterizing it as a non-polar solvent.

• Indicates molecular polarity.
• High dipole moment = polar.
• Low dipole moment = non-polar.

Hydrogen Bonding

Hydrogen bonding is a critical intermolecular force that occurs between molecules containing hydrogen atoms bonded to electronegative elements like oxygen, nitrogen, or fluorine. It plays a vital role in the properties of substances, including their boiling points, solubility, and overall stability. In polar solvents like methanol, hydrogen bonding is particularly pronounced due to the presence of the hydroxyl group.

In methanol, the hydrogen atom in the \(-\text{OH}\) group can form hydrogen bonds with other molecules, significantly strengthening its ability to act as a solvent for polar compounds. This interaction facilitates the dissolution and stability of polar solutes. On the other hand, non-polar substances like toluene do not form hydrogen bonds, limiting their solubility range to non-polar compounds.

• Formed between hydrogen and electronegative atoms.
• Enhances solubility of polar substances.
• Not present in non-polar solvents like toluene.