Solubility
Like dissolves like, solubility rules for ionic compounds, and the role of intermolecular forces. Hydrogen bonding, polarity, and lattice energy determine whether a substance dissolves in water or organic solvents.
Hexane
C₆H₁₄
Ethanol
C₂H₅OH
Hexane is a nonpolar hydrocarbon with no ability to form hydrogen bonds. Mixing hexane with water would require breaking the strong hydrogen bond network in water without any compensating favorable interactions.
Ethanol is completely miscible with water because its hydroxyl group forms strong hydrogen bonds with water molecules. The short two-carbon chain is not large enough to overcome this favorable polar interaction.
Cholesterol
C₂₇H₄₆O
Glucose
C₆H₁₂O₆
Cholesterol is nearly insoluble in water despite having one hydroxyl group. Its large hydrophobic steroid ring system and long hydrocarbon tail overwhelm the single polar group, making the overall molecule strongly hydrophobic.
Glucose is extremely soluble in water (~910 g/L) because its five hydroxyl groups form extensive hydrogen bonds with water molecules. The molecule is small and highly polar relative to its size.
1-Octanol
C₈H₁₇OH
Methanol
CH₃OH
1-Octanol is nearly insoluble in water because its eight-carbon hydrocarbon chain is too large and nonpolar. The single hydroxyl group at the end cannot overcome the hydrophobic effect of the long chain.
Methanol is fully miscible with water because its single carbon chain is too small to disrupt the hydrogen bonding network. The hydroxyl group dominates the molecule's properties.
Silver chloride
AgCl
Sodium chloride
NaCl
AgCl is nearly insoluble in water (Ksp = 1.77 x 10⁻¹⁰). The Ag⁺ ion has significant covalent character in its bonding with Cl⁻, creating a very strong lattice that water's ion-dipole forces cannot easily break apart.
NaCl is highly soluble in water (360 g/L) because the strong ion-dipole interactions between water and Na⁺/Cl⁻ ions easily overcome the lattice energy. The small, highly charged Na⁺ ion is particularly well hydrated.