Question

Which substance, \(\mathrm{SO}_{2}\) or \(\mathrm{CO}_{2}\), is likely to be more soluble in water?

Short answer

Sulfur dioxide (\(\mathrm{SO}_{2}\)) is more likely to be soluble in water than carbon dioxide (\(\mathrm{CO}_{2}\)) as it is a polar molecule and can form dipole-dipole interactions and hydrogen bonds with water.

Step-by-step solution

Identifying the Polarity and Molecular Structure of \(\mathrm{SO}_{2}\) and \(\mathrm{CO}_{2}\)

We need to first identify the polarity and structure of the two gases. Both \(\mathrm{SO}_{2}\) and \(\mathrm{CO}_{2}\) are molecular compounds. \(\mathrm{SO}_{2}\) is a polar molecule due to the difference in electronegativity between sulfur and oxygen and its bent molecular structure. \(\mathrm{CO}_{2}\), however, is a linear non-polar molecule because the electronegativity difference between carbon and oxygen gets nullified due to its linear structure.

Understanding Solubility in Relation to Polarity

According to the 'like dissolves like' principle, polar solvents like water dissolve polar solutes better than nonpolar solutes due to their ability to form dipole-dipole interactions and hydrogen bonds.

Decide which Gas is more Soluble

Given that \(\mathrm{SO}_{2}\) is a polar molecule and \(\mathrm{CO}_{2}\) is a nonpolar molecule, it can be concluded that \(\mathrm{SO}_{2}\) is more likely to be soluble in water than \(\mathrm{CO}_{2}\). This is because \(\mathrm{SO}_{2}\) can form dipole-dipole interactions and hydrogen bonds with water, while \(\mathrm{CO}_{2}\) cannot.

Key concepts

Molecular Polarity

Understanding molecular polarity is fundamental when exploring the solubility of different substances in water. A molecule's polarity is determined by its shape and the electronegativity differences among its atoms. When the electronegativity difference leads to an uneven distribution of electron density, a molecule is considered polar. This results in partial positive and negative charges at different ends, creating what is known as a dipole.

For example, sulfur dioxide (SO₂) has a bent shape, and the difference in electronegativity between sulfur and oxygen atoms makes it a polar molecule. In contrast, carbon dioxide (CO₂), despite having polar bonds, is a non-polar molecule because its linear structure causes the electronegativity differences to cancel out. The molecule has no overall charge, hence there is no permanent dipole.

Dipole-Dipole Interactions

Dipole-dipole interactions occur between polar molecules that have permanent dipoles. These interactions arise because the positive end of one dipole is attracted to the negative end of another. They play a crucial role when it comes to the solubility of substances in polar solvents such as water.

Considering sulfur dioxide (SO₂), its polarity allows it to engage in dipole-dipole interactions with water molecules, which are also polar. This mutual attraction between the two substances increases SO₂'s solubility in water. Conversely, carbon dioxide (CO₂), being non-polar, cannot form such interactions with water, which limits its solubility.

Hydrogen Bonding

Hydrogen bonding is a special kind of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom such as oxygen, nitrogen, or fluorine. It is the strongest type of dipole-dipole attraction and significantly affects the solubility of compounds in water.

Water molecules are capable of hydrogen bonding because of the presence of hydrogen atoms bonded to oxygen. SO₂, with its polar nature, can participate in these interactions as it can act as both a hydrogen bond donor and acceptor when interacting with water. This capacity for hydrogen bonding greatly enhances the solubility of SO₂ in water. On the other hand, CO₂, due to its lack of polarity, cannot participate in hydrogen bonding, reducing its solubility.

Like Dissolves Like Principle

The principle of 'like dissolves like' is a simple yet powerful rule in chemistry, which states that polar substances tend to dissolve well in polar solvents, and non-polar substances dissolve better in non-polar solvents. This is because similar types of molecular interactions can occur between the solute and the solvent, leading to a more stable solution.

Applying this principle, we can infer that the polar SO₂ dissolves readily in polar water through dipole-dipole interactions and hydrogen bonding. Conversely, the non-polar CO₂ does not dissolve as well in water due to the absence of these interactions. Understanding this principle helps us predict the solubility of different substances in various solvents, essential knowledge for many applications in chemistry and industry.