Water - Level 2 Flashcards
(7 cards)
Why does water weaken ionic interactions between charged particles like Na⁺ and Cl⁻?
a) Water’s high dielectric constant and polarity allow it to shield charges
b) Water is nonpolar and cannot interact with ions
c) Water forms covalent bonds with ions
d) Water increases the distance between molecules by forming micelles
Answer: a) Water’s high dielectric constant and polarity allow it to shield charges
Explanation: Water’s polarity allows it to surround charged particles and form hydration shells. Its high dielectric constant reduces the strength of the electrostatic force between them (per Coulomb’s Law), allowing ions to separate more easily and dissolve. This weakens ionic interactions and increases solubility.
When we say water weakens ionic interactions, which interaction is being weakened?
a) The interaction between water and the ions
b) The hydrogen bonding between water molecules
c) The ionic bond between the ions themselves (e.g., Na⁺ and Cl⁻)
d) The covalent bond within the solute
Answer: c) The ionic bond between the ions themselves (e.g., Na⁺ and Cl⁻)
Explanation: Water weakens the ionic bond between the charged ions themselves, such as Na⁺ and Cl⁻ in solid NaCl. This occurs because water’s polarity and high dielectric constant allow it to surround each ion with a hydration shell, shielding the charges and reducing the electrostatic force between them. As a result, the ions separate and dissolve, increasing solubility.
Why is water’s ability to weaken electrostatic interactions important for biological systems?
a) It helps water donate protons to neutralize charged ions
b) It allows enzymes to form covalent bonds with substrates
c) It prevents water molecules from forming hydrogen bonds with solutes
d) It enables ion separation and solubility, supporting processes like protein folding and transport
Answer: d) It enables ion separation and solubility, supporting processes like protein folding and transport
Explanation: Water weakens electrostatic interactions by surrounding charged particles and shielding their charges. This makes it easier to separate ions, which facilitates the dissolution of salts, ion transport, protein folding, and other biological functions. The high dielectric constant of water plays a key role in reducing the force between charged groups, which is essential for maintaining proper biochemical activity.
Why is micelle formation considered thermodynamically favorable in water?
a) Hydrophobic tails repel each other, forming a low-energy structure
b) Hydrogen bonds form between nonpolar molecules
c) Clustering of hydrophobic tails increases water ordering
d) Clustering reduces water ordering, increasing entropy and decreasing free energy
Answer: d) Clustering reduces water ordering, increasing entropy and decreasing free energy
Explanation: Micelle formation is thermodynamically favorable because it is driven by the hydrophobic effect. When nonpolar tails cluster, water is released from ordered structures surrounding them, which increases entropy (ΔS). This increase in entropy leads to a decrease in free energy (ΔG), making the process spontaneous.
Why is the clustering of hydrophobic regions (e.g., in micelles) thermodynamically favorable?
a) It increases enthalpy and heat absorption
b) It increases entropy by freeing water molecules, lowering ΔG
c) It decreases entropy by forming ordered water cages
d) It creates more hydrogen bonding between solutes
Answer: b) It increases entropy by freeing water molecules, lowering ΔG
Explanation: Clustering of hydrophobic regions causes structured water molecules to be released into the bulk solvent, reducing water ordering. This increases entropy (ΔS), which lowers ΔG according to the equation ΔG = ΔH – TΔS. Even if enthalpy doesn’t change much, the entropy increase can make ΔG negative, making the process spontaneous and thermodynamically favorable.
Why does the formation of clathrate cages around nonpolar molecules in water decrease entropy?
a) Because water molecules gain energy from hydrogen bonding
b) Because water molecules are released into bulk solvent
c) Because water molecules become more ordered to preserve hydrogen bonding
d) Because nonpolar molecules ionize and disrupt the solvent
Answer: c) Because water molecules become more ordered to preserve hydrogen bonding
Explanation: Water forms clathrate cages around nonpolar molecules to maintain its hydrogen bonding network. These cages are highly ordered structures that reduce molecular randomness. This decreases entropy (ΔS), which is unfavorable for spontaneity (since lower entropy contributes to a higher ΔG).
How does micelle formation overcome the unfavorable entropy change caused by clathrate formation?
a) By clustering hydrophobic regions and freeing water molecules
b) By decreasing enthalpy through hydrophobic bonding
c) By increasing polarity of water molecules
d) By breaking covalent bonds
Answer: a) By clustering hydrophobic regions and freeing water molecules
Explanation: Micelles form when hydrophobic tails cluster together, minimizing their contact with water. This reduces the number of ordered water cages (clathrates) that must form. As a result, structured water is released into bulk solvent, entropy increases, and ΔG becomes more negative, making the process spontaneous and thermodynamically favorable.
