Question

Which among the following compound is hydrophilic? (A) \(\mathrm{CH}_{3}-\mathrm{CH}_{3}\) (B) \(\mathrm{CH}_{3}-\mathrm{OH}\) (C) \(\mathrm{CH}_{3}-\mathrm{Cl}\) (D) All of these

Short answer

(B) \(\mathrm{CH}_{3}-\mathrm{OH}\) (Methanol) is the only hydrophilic compound among the given options, as it is polar and capable of forming hydrogen bonds with water.

Step-by-step solution

Understand the concept of Hydrophilic

The term 'hydrophilic' describes substances that can mix with or dissolve in water. This happens because of the fact that water is a polar molecule - it has a slight positive charge on one side and a slight negative charge on the other. Substances that can interact with these charges through hydrogen bonds or ion-dipole interactions are considered hydrophilic.

Evaluate the polarity of each compound

Look each compound to determine if it is polar or not. Polar molecules can form hydrogen bonds or dipole-dipole interactions with water. (A) Ethane (\(\mathrm{CH}_{3}-\mathrm{CH}_{3}\)): This compound is non-polar as the distribution of electrons and charges is symmetric. (B) Methanol (\(\mathrm{CH}_{3}-\mathrm{OH}\)): This molecule is polar. The oxygen atom attracts the electrons of the hydrogen atom of the hydroxyl group, thus creating a partial negative charge on the oxygen and a partial positive charge on the hydrogen. This means that it can form hydrogen bonds with water. (C) Chloromethane (\(\mathrm{CH}_{3}-\mathrm{Cl}\)): Although Chloromethane is technically a polar molecule because chlorine is more electronegative than carbon, thus creating a dipole. However, the polarity is not enough to form hydrogen bonds with water.

Determine which substance is Hydrophilic

Based on the information gathered in Step 2, Methanol is the only compound that can form hydrogen bonds with water, making it the only hydrophilic compound among the given options. Thus, the correct answer is (B) \(\mathrm{CH}_{3}-\mathrm{OH}\).

Key concepts

Polarity of Molecules

Polarity is a term used to describe the distribution of electrical charge over the atoms joined by a bond. In simpler terms, a polar molecule is one that has a positive electrical charge on one side and a negative charge on the other. This imbalance in charge distribution occurs because atoms in the molecule have differing abilities to attract electrons, known as electronegativity. For example, in a water molecule (H_2O), oxygen is more electronegative than hydrogen, resulting in a partial negative charge around the oxygen and a partial positive charge around the hydrogens.

When we consider compounds like methane (CH_4) or ethane ((CH_3)_2, they are non-polar because their symmetry ensures an even distribution of charge. However, as soon as you have a molecule like methanol (CH_3OH), the presence of the highly electronegative oxygen turns the molecule polar. Methanol's polarity allows it to engage in interactions with other polar molecules, especially water.

Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole interaction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom—such as nitrogen, oxygen, or fluorine—and another electronegative atom. This bond is relatively strong compared to other dipole-dipole interactions, yet weaker than covalent or ionic bonds. An example of hydrogen bonding is the interaction between water (H_2O) molecules, where the hydrogen of one molecule is attracted to the oxygen of another.

Hence, compounds that contain hydrogen atoms attached to electronegative atoms can participate in hydrogen bonding. Methanol (CH_3OH) fits this criterion as the oxygen in its hydroxyl group can form hydrogen bonds with water. This is not the case with non-polar molecules like ethane, which lacks the electronegative atom necessary to form such bonds.

Solubility in Water

Solubility in water is largely determined by the ability of a compound to form hydrogen bonds or engage in dipole-dipole interactions with water molecules, as water itself is a highly polar molecule. Compounds that are polar or capable of hydrogen bonding, such as glucose or methanol, tend to dissolve well in water. This property is termed 'hydrophilicity.' There's a common saying, 'like dissolves like,' meaning that polar substances dissolve in polar solvents, and non-polar substances dissolve in non-polar solvents.

Solubility isn't determined solely by polarity, though. The molecule's size and the strength of its interactions also play significant roles. Methanol, with its polar hydroxyl group (-OH), can form strong hydrogen bonds with water, granting it substantial solubility. On the other hand, non-polar molecules like ethane have no such capability, rendering them hydrophobic or 'water-fearing.'