BSC 450 EXAM 1 Questions with Correct Solutions

BSC 450 EXAM 1 Questions with Correct Solutions


Question:
1. Water bond angle

Answer:
~104.5° (H-O-H), slightly less than tetrahedral 109.5° because lone pairs repel more than
bonding pairs


Question:
2. Hydrogen bond donor

Answer:
An atom with an H attached to something electronegative (O-H, N-H) — the H is available to
bond


Question:
3. Hydrogen bond acceptor

Answer:
An electronegative atom (O or N) with a lone pair that accepts the H


Question:
4. C-H bonds and H-bonding

Answer:
C-H does NOT participate in hydrogen bonding — carbon is only slightly more electronegative
than H


Question:
5. H-bonds per water molecule

Answer:
Max 4 in ice; averages only 3.4 in liquid water due to constant motion ("flickering clusters")


Question:
6. Bond energy ranking (weak to strong)

Answer:
Van der Waals < hydrogen bonds (~1-5 kcal/mol) < ionic interactions < covalent bonds
(~80-100+ kcal/mol)


Question:
7. Hydrophilic

,Answer:
"Water-loving" — polar/charged, dissolves well in water


Question:
8. Hydrophobic

Answer:
"Water-fearing" — nonpolar, does not dissolve well in water


Question:
9. Amphipathic

Answer:
A molecule with both a polar/charged region and a nonpolar region (e.g., fatty acids)


Question:
10. Micelle

Answer:
Sphere formed by amphipathic molecules: polar/charged heads face outward toward water,
nonpolar tails cluster inward


Question:
11. Hydrophobic effect (what drives it)

Answer:
Entropy, NOT direct attraction — clustering nonpolar groups releases ordered water into
bulk solution, increasing entropy


Question:
12. Hydrophobic effect applications

Answer:
Protein folding, protein-protein association, micelle formation, steroid hormone-receptor
binding, odorant binding


Question:
13. Van der Waals interactions (2 components)

Answer:
Attractive (London dispersion, from polarizability) dominates at longer range; Repulsive
(steric) dominates at short range


Question:
14. Van der Waals biological role

,Answer:
Stabilizes DNA base stacking, determines steric complementarity, helps bind polarizable
ligands


Question:
15. Coulomb's law variables

Answer:
F = Q1Q2/(εr²) — charge magnitude, dielectric constant, distance (concept only, no
calculation needed)


Question:
16. Why N2 and O2 are poorly soluble in water

Answer:
Share electrons equally — no dipole — nonpolar


Question:
17. Why CO2 is poorly soluble despite polar bonds

Answer:
Linear geometry makes the two dipoles cancel out — net nonpolar


Question:
18. Why water is polar (compare to CO2)

Answer:
Bent geometry (2 lone pairs) means water's two dipoles do NOT cancel — net polar


Question:
19. DNA and non-covalent interactions

Answer:
Uses all 4 types at once: ionic (phosphate backbone), H-bonds (base pairing), van der Waals
(base stacking), hydrophobic effect (bases tucked inside) Ì


Question:
20. Water as a reactant example

Answer:
Carbonic anhydrase: CO2 + H2O HCO3- + H+ (CO2 transport in blood)


Question:
21. Hydrolysis

, Answer:
Water breaks a bond (adds -OH and -H across it)


Question:
22. Condensation/dehydration reaction

Answer:
Two molecules join and release water


Question:
23. Colligative properties

Answer:
Boiling point, melting point, osmolarity — depend ONLY on number of dissolved particles, not
identity


Question:
24. Why NaCl has 2x the colligative effect of glucose

Answer:
NaCl dissociates into 2 particles (Na+, Cl-); glucose stays as 1 particle


Question:
25. Noncolligative properties

Answer:
Viscosity, surface tension, taste, color — depend on chemical identity of solute


Question:
26. Osmosis (direction of water movement)

Answer:
Water moves from high water concentration to low water concentration (toward higher solute
concentration)


Question:
27. Isotonic

Answer:
Equal solute concentration inside/outside cell — no net water movement


Question:
28. Hypertonic

Answer:
More solute outside — water LEAVES the cell (shrinks)