Which of the following in each pair is likely to be more soluble in water: (c) HCl or ethyl chloride (CH₃CH₂Cl)? Explain in each case.

Verified step by step guidance

1. Step 1: Understand the concept of 'like dissolves like'. This means that polar substances tend to dissolve in polar solvents, and nonpolar substances tend to dissolve in nonpolar solvents. Water is a polar solvent.
2. Step 2: Identify the polarity of the substances. HCl is a polar molecule because it has a polar bond due to the difference in electronegativity between hydrogen and chlorine. Ethyl chloride (CH3CH2Cl) is also polar, but less so than HCl because the electronegativity difference between carbon and hydrogen is less than that between hydrogen and chlorine.
3. Step 3: Consider the ability of the substances to form hydrogen bonds with water. HCl can form hydrogen bonds with water because chlorine is a highly electronegative atom. Ethyl chloride, on the other hand, cannot form hydrogen bonds with water because it does not have a hydrogen atom bonded to an electronegative atom.
4. Step 4: Based on the above considerations, HCl is likely to be more soluble in water than ethyl chloride. This is because HCl is more polar and can form hydrogen bonds with water, while ethyl chloride is less polar and cannot form hydrogen bonds with water.
5. Step 5: Remember that these are general guidelines and actual solubility can be influenced by other factors such as temperature and pressure.

Key Concepts

Polarity and Solubility

Polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have a significant difference in electronegativity between their atoms, tend to dissolve well in polar solvents like water. This is due to the 'like dissolves like' principle, where polar solutes are more soluble in polar solvents, while nonpolar solutes are better dissolved in nonpolar solvents.

Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. In the case of HCl, the molecule can form hydrogen bonds with water, enhancing its solubility. Ethyl chloride, being a nonpolar molecule, lacks the ability to form such interactions, making it less soluble in water.

Molecular Structure and Functional Groups

The molecular structure and functional groups of a compound significantly influence its solubility. HCl is a simple diatomic molecule that ionizes in water to form H⁺ and Cl⁻ ions, increasing its solubility. In contrast, ethyl chloride has a larger hydrocarbon structure with a chlorine atom, which does not ionize and is less compatible with water, leading to lower solubility.