Practice Questions

Wax is a non-polar, hydrophobic surface. The polar water molecules are more strongly attracted to each other via hydrogen bonding (cohesion) than they are to the wax surface (adhesion). This causes the water to minimize its contact with the wax and form spherical beads.

Imbibition is the physical adsorption of water onto the hydrophilic surfaces of macromolecules (proteins, polysaccharides) and cell walls inside the seed. This matric potential is an extremely negative component of water potential, creating a massive driving force for water uptake.

Evaporation is a physical change, not a chemical one. The covalent bonds within the molecule are not broken. The energy (latent heat of vaporization) is used to overcome the attractive intermolecular hydrogen bonds holding the water molecules together in the liquid phase.

Water is the solvent in which buffers operate, and its ionization constant (Kw) is fundamental to the pH scale. A buffer's equilibrium (e.g., H₂CO₃ ⇌ H⁺ + HCO₃⁻) involves the release or absorption of H⁺ ions produced by water's interaction with the buffer components, resisting pH change.

Wilting occurs when transpiration exceeds water uptake. Cells lose water, decreasing their water potential and turgor pressure. The protoplast no longer presses firmly against the cell wall, and the non-woody tissues lose their rigidity, causing the plant to droop.

The hydration of CO₂ (CO₂ + H₂O → H₂CO₃) produces carbonic acid, which dissociates into H⁺ and HCO₃⁻. The release of H⁺ lowers the pH. This is a major source of acidity, not just the dissolution of pre-formed lactic acid.

Water, as a major component of synovial fluid and serous fluid, forms a cohesive, slippery film. The high cohesion of water molecules allows the fluid to resist being squeezed out from between surfaces under pressure, providing an excellent lubricating layer.

An increase in plasma solute (NaCl) concentration decreases its water potential. Water moves by osmosis from the area of higher water potential (inside cells) to the area of lower water potential (blood plasma), leading to cellular dehydration and increased blood volume/pressure.

Water molecules form highly ordered "cage-like" structures around exposed non-polar groups, which decreases entropy. To minimize this, water forces non-polar groups to aggregate, freeing the caged water and increasing overall entropy. This entropic force is the hydrophobic effect.

While water's polarity and geometry are contributing factors, the direct reason for its abnormally high boiling point is the strength and number of intermolecular hydrogen bonds. A large amount of thermal energy is required to disrupt these attractive forces to allow molecules to escape as vapor.