Explain the boiling points of Group 16 hydrides and the miscibility of CCl4 and CH3OH with water.

For $\text{H}_2\text{S}$, $\text{H}_2\text{Se}$, and $\text{H}_2\text{Te}$, the boiling points increase with increasing molecular mass. This is due to an increase in the number of electrons, leading to stronger London dispersion forces between molecules.

$\text{H}_2\text{O}$ has an exceptionally high boiling point compared to the other hydrides because oxygen is highly electronegative and has lone pairs, allowing water molecules to form strong hydrogen bonds with each other. Hydrogen bonding is a much stronger intermolecular force than the dipole-dipole interactions and London dispersion forces present in the other hydrides.

2. Miscibility of $\text{CCl}_4$ and $\text{CH}_3\text{OH}$ with water

Tetrachloromethane ($\text{CCl}_4$) is a nonpolar molecule because its tetrahedral geometry causes the bond dipoles to cancel out. It only exhibits weak London dispersion forces. Water is a polar molecule with strong hydrogen bonds. Since $\text{CCl}_4$ cannot form hydrogen bonds with water, it cannot effectively disrupt water's strong hydrogen bonding network, making them immiscible.

Methanol ($\text{CH}_3\text{OH}$) is a polar molecule containing an -OH group. This group allows methanol to form hydrogen bonds with water molecules. Because both methanol and water can form hydrogen bonds, they are miscible in all proportions.

3. Solubility of methanoic acid and octanoic acid in water

Methanoic acid ($\text{HCOOH}$) is a small carboxylic acid. Its polar -COOH group can form strong hydrogen bonds with water molecules. The small nonpolar part (a single hydrogen atom) does not significantly impede this interaction, making it soluble in water.

Octanoic acid ($\text{C}_7\text{H}_{15}\text{COOH}$) also has a polar -COOH group capable of forming hydrogen bonds. However, it possesses a long, nonpolar hydrocarbon chain ($\text{C}_7\text{H}_{15}$). This large hydrophobic chain disrupts the hydrogen bonding network of water, and the energy gained from hydrogen bonding with the -COOH group is insufficient to overcome this disruption, making octanoic acid much less soluble.