Q: Which equation correctly represents the calculation of the total dipole moment ($\mu$) for a molecule with two bond dipoles at an angle $\theta$?

$\mu = \sqrt{\mu_1^2 + \mu_2^2 + 2\mu_1\mu_2 \cos \theta}$

Question 1

Which of the following best explains why water is a polar molecule?

Accepted Answer

Water has a bent geometry and a significant difference in electronegativity between oxygen and hydrogen, resulting in a net dipole moment.

Question 2

Which equation correctly represents the calculation of the total dipole moment ($\mu$) for a molecule with two bond dipoles at an angle $	heta$?

Accepted Answer

$\mu = \sqrt{\mu_1^2 + \mu_2^2 + 2\mu_1\mu_2 \cos 	heta}$

Question 3

Which of the following molecules is nonpolar despite having polar bonds, and why?

Accepted Answer

CO$_2$, because its linear geometry causes the bond dipoles to cancel each other out.

Question 4

Which of the following statements about hydrogen bonds is TRUE?

Accepted Answer

A hydrogen bond is a non-covalent interaction where a hydrogen atom covalently bonded to an electronegative atom (like O or N) interacts with another electronegative atom with a lone pair.

Question 5

Which of the following best describes the hydrophobic effect?

Accepted Answer

It is the increase in entropy of water molecules when hydrophobic molecules cluster together, minimizing the ordering of water.

Question 6

A buffer solution is prepared by mixing acetic acid ($\mathrm{CH_3COOH}$) and sodium acetate ($\mathrm{CH_3COONa}$). If the $pK_a$ of acetic acid is 4.76, what is the pH of the solution when the concentration of acetic acid equals that of sodium acetate?

Accepted Answer

pH = 4.76

Question 7

Which of the following best explains why amphipathic molecules form micelles in water?

Accepted Answer

Their hydrophobic regions cluster together to minimize contact with water, while hydrophilic regions interact with water.

Question 8

Which of the following is the correct Henderson-Hasselbalch equation for a weak acid HA and its conjugate base A$^-$?

Accepted Answer

$\mathrm{pH} = \mathrm{p}K_a + \log \left( \dfrac{[\mathrm{A}^-]}{[\mathrm{HA}]} \right)$

Question 9

A solution contains 0.1 M lactic acid ($pK_a = 3.86$) and 0.01 M sodium lactate. What is the pH of the solution? (Use the Henderson-Hasselbalch equation.)

Accepted Answer

pH = 3.86 + \log \left( \dfrac{0.01}{0.1} \right) = 3.86 + (-1) = 2.86

Question 10

Which of the following statements about buffer capacity is TRUE?

Accepted Answer

Buffer capacity increases as the concentrations of both the weak acid and its conjugate base increase.

Question 11

Which of the following best describes the role of the bicarbonate buffer system in blood?

Accepted Answer

It maintains blood pH by converting CO$_2$ to HCO$_3^-$ and H^+$, buffering changes in acid/base balance.

Question 12

Which of the following is a correct statement about the relationship between pH and the protonation state of a weak acid?

Accepted Answer

When pH = pK$_a$, the concentrations of the acid and its conjugate base are equal.

Question 13

Which of the following interactions is NOT considered a non-covalent interaction stabilizing biomacromolecules?

Accepted Answer

Disulfide (S-S) bonds

Question 14

A protein is found to denature at low pH. Which of the following best explains this observation?

Accepted Answer

Low pH increases the concentration of H$^+$, which can disrupt ionic interactions and hydrogen bonds stabilizing the protein's structure.

Question 15

Which of the following best describes the difference between hydrophilic and hydrophobic substances?

Accepted Answer

Hydrophilic substances are polar or charged and dissolve in water; hydrophobic substances are nonpolar and do not dissolve in water.

Question 16

Which of the following is the correct expression for the ion product constant for water ($K_w$) at 25°C?

Accepted Answer

$K_w = [\mathrm{H}^+][\mathrm{OH}^-] = 1.0 	imes 10^{-14}$

Question 17

A solution has a hydrogen ion concentration of $1 	imes 10^{-5}$ M. What is its pH?

Accepted Answer

pH = 5

Question 18

Which of the following best explains why van der Waals interactions are important in biological systems?

Accepted Answer

They are weak individually but collectively stabilize the three-dimensional structure of macromolecules.

Water, Non-Covalent Interactions, and Acid-Base Chemistry in Biochemistry Ch 2

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