Q: Which of the following is a correct application of the Henderson-Hasselbalch equation for a buffer system?

pH = $$pK_a + \log \left( \frac{[\text{Salt}]}{[\text{Acid}]} \right)$$

Question 1

Which of the following statements best explains why sodium dodecylsulfate (SDS) is effective at denaturing proteins in biochemical experiments?

Accepted Answer

SDS disrupts noncovalent interactions by binding to hydrophobic regions, causing proteins to unfold.

Question 2

Which functional group is most likely to increase the acidity of a molecule through the inductive effect?

Accepted Answer

A nitro group ($$-NO_2$)

Question 3

A peptide contains the following groups: N-terminal ($$pK_a = 9.5$$), C-terminal ($$pK_a = 2.0$$), and a lysine side chain ($$pK_a = 10.5). $$What is the net charge of the peptide at pH 7?

Accepted Answer

+1

Question 4

Which intermolecular force is primarily responsible for the solubility of NaCl in water?

Accepted Answer

Ion-dipole interactions

Question 5

Given the following pKa values: acetic acid ($$pK_a = 4.8$$), trichloroacetic acid ($$pK_a = 0.7$$), and monochloroacetic acid ($$pK_a = 2.9$$), which acid is the strongest and why?

Accepted Answer

Trichloroacetic acid, because the electron-withdrawing effect of three chlorines stabilizes the conjugate base.

Question 6

Which of the following molecules is most likely to be soluble in hexane?

Accepted Answer

Octane ($$C_8H_{18})$$

Question 7

A solution contains a weak acid ($$HA) $$and its conjugate base ($$A^-) at $$equal concentrations. What is the pH of the solution relative to the acid's $$pK_a$$?

Accepted Answer

pH = $$pK_a$$

Question 8

Which statement best describes the difference between the inductive effect and the resonance (mesomeric) effect?

Accepted Answer

Inductive effect is transmitted through sigma bonds and decreases with distance, while resonance effect involves delocalization through pi bonds and is not distance-dependent.

Question 9

Ibuprofen has a $$pK_a of 4.4. At $$which pH will ibuprofen be more than 99% deprotonated (negatively charged)?

Accepted Answer

pH 6.4

Question 10

Which of the following best explains why proteins fold into specific three-dimensional structures in aqueous environments?

Accepted Answer

Hydrophobic amino acids aggregate in the core, minimizing contact with water, while hydrophilic amino acids remain on the surface.

Question 11

Which of the following functional groups is most likely to participate in hydrogen bonding with water?

Accepted Answer

Carboxyl ($$-COOH)$$

Question 12

A buffer solution is prepared using acetic acid ($$pK_a = 4.8) $$and sodium acetate. What is the pH of the buffer if the ratio $$[A^-]/[HA] = 10$$?

Accepted Answer

pH = $$4.8 + 1 = 5.8$$

Question 13

Which of the following best describes the hydrophobic effect in biological systems?

Accepted Answer

It is the tendency of nonpolar groups to aggregate in aqueous environments, minimizing the ordering of water molecules.

Question 14

Which statement is true regarding the solubility rule 'like dissolves like'?

Accepted Answer

Nonpolar substances are usually soluble in nonpolar solvents.

Question 15

Which of the following is a correct application of the Henderson-Hasselbalch equation for a buffer system?

Accepted Answer

pH = $$pK_a + \log \left( \frac{[	ext{Salt}]}{[	ext{Acid}]} ight)$$

Question 16

Which of the following molecules is most likely to be nonpolar?

Accepted Answer

Carbon dioxide ($$CO_2)$$

Question 17

Which of the following statements about the effect of pH on the ionization of weak acids is correct?

Accepted Answer

At pH much higher than the $$pK_a$$, the weak acid is mostly deprotonated.

Question 18

Which of the following is NOT a consequence of resonance (mesomeric) effects in molecules?

Accepted Answer

Transmission of electron density exclusively through sigma bonds.

Question 19

Which of the following is the strongest type of noncovalent interaction found in biological molecules?

Accepted Answer

Hydrogen bonds

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