Practice Questions

The solvent evaporates quickly. This phase change from liquid to vapor requires the absorption of its latent heat of vaporization. This heat is drawn from the skin, causing a rapid and intense cooling sensation, even more pronounced than with water due to its higher volatility.

In ice, a rigid tetrahedral lattice yields exactly 4 H-bonds per molecule. In liquid water, thermal energy causes the bonds to constantly flicker, break, and re-form. This results in a dynamic, fluctuating network where the average number is closer to 3.4 rather than the maximum 4.

In condensation (dehydration) synthesis, the new covalent bond (e.g., C-N peptide bond) is formed by removing a hydroxyl group from one monomer and a hydrogen from another. The byproduct of this bond formation is a single water molecule.

The curvature of water menisci in the cell walls of the leaf mesophyll generates the tension that pulls the water column. As cells lose water during wilting, these menisci recede, reducing the curvature and thus the tension. This feedback reduces the pulling force, limiting further water loss.

The dissolution process disrupts the local, ordered structure of both the solute and the water, distributing the solute molecules randomly throughout the solvent. This increase in randomness represents an increase in the overall entropy (ΔS > 0) of the system, which is a driving force for dissolution.

Dehydration alters the precise ionic concentrations of Na⁺, K⁺, and Ca²⁺ outside and inside neurons. This disrupts the membrane potential, action potential generation, and neurotransmitter release, leading to impaired cognitive function. The brain is highly sensitive to osmotic shifts.

Water molecules are integral to DNA structure. They form a "spine of hydration" in the minor groove and interact with the charged phosphate backbone, shielding negative charges and stabilizing the B-form of DNA. The hydrophobic effect also drives base stacking.

Protons (H⁺) do not diffuse as free ions. Instead, they "hop" along a chain of hydrogen-bonded water molecules (Grotthuss mechanism). A water molecule accepts a proton on one side, and a different proton is released from the other side. This facilitates extremely rapid proton transfer in biological systems.

Water moves from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration). It is the water potential gradient, not the solute concentration gradient per se, that provides the driving force.

A high dielectric constant, by definition, weakens the force of attraction between charges. This stabilizes dissolved ions in solution, preventing their precipitation and making them available for reactions. It also affects the pKa of acids by stabilizing their conjugate bases.