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

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

Q: Which equation is the Henderson-Hasselbalch equation for a weak acid and its conjugate base?

$\mathrm{pH} = \mathrm{pK}_a + \log \left( \frac{[\text{Conjugate base}]}{[\text{Weak acid}]} \right)$

Question 1

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

Accepted Answer

Water has a bent geometry and oxygen is more electronegative than hydrogen, causing unequal sharing of electrons and a net dipole moment.

Question 2

Given the electronegativity values: Oxygen (3.5), Nitrogen (3.0), Carbon (2.5), Hydrogen (2.1), which bond is expected to be the most polar?

Accepted Answer

O-H

Question 3

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

Accepted Answer

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

Question 4

Why is carbon dioxide ($CO_2$) considered a nonpolar molecule despite having polar bonds?

Accepted Answer

The linear geometry causes the individual bond dipoles to cancel each other out, resulting in zero net dipole moment.

Question 5

Which of the following is NOT a type of non-covalent interaction stabilizing biomolecules?

Accepted Answer

Disulfide (S-S) bonds

Question 6

A solution contains a weak acid, HA, and its conjugate base, A$^-$. If the concentrations of HA and A$^-$ are equal, what is the relationship between pH and pK$_a$?

Accepted Answer

pH equals pK$_a$

Question 7

Which equation is the Henderson-Hasselbalch equation for a weak acid and its conjugate base?

Accepted Answer

$\mathrm{pH} = \mathrm{pK}_a + \log \left( \frac{[	ext{Conjugate base}]}{[	ext{Weak acid}]} ight)$

Question 8

Which of the following best describes the hydrophobic effect?

Accepted Answer

Hydrophobic molecules cluster together in water, increasing the entropy of the surrounding water molecules.

Question 9

A buffer solution is most effective when:

Accepted Answer

The concentrations of weak acid and conjugate base are high and the pH is close to the pK$_a$.

Question 10

Which of the following is a correct statement about hydrogen bonds in water?

Accepted Answer

Each water molecule can participate in up to four hydrogen bonds due to its tetrahedral geometry.

Question 11

Which of the following substances is amphipathic?

Accepted Answer

Sodium palmitate

Question 12

If the pH of a solution is 5, what is the concentration of hydrogen ions ($[H^+]$) in mol/L?

Accepted Answer

$[H^+] = 1 	imes 10^{-5}$

Question 13

Which of the following best describes a micelle?

Accepted Answer

A spherical arrangement of amphipathic molecules in water with hydrophobic regions buried inside and hydrophilic regions exposed to water.

Question 14

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

Accepted Answer

$K_w = [H^+][OH^-]$

Question 15

Which of the following statements about buffer capacity is correct?

Accepted Answer

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

Question 16

A patient is experiencing respiratory acidosis due to hypoventilation. Which buffer system in the blood is primarily responsible for minimizing pH changes?

Accepted Answer

Bicarbonate buffer system ($H_2CO_3/HCO_3^-$)

Question 17

Which of the following is true regarding the relationship between pH and the protonation state of a weak acid?

Accepted Answer

When pH < pK$_a$, the weak acid is mostly protonated.

Question 18

Which of the following interactions is responsible for the solubility of ionic compounds like KCl in water?

Accepted Answer

Ion-dipole interactions

Question 19

A buffer is prepared using acetic acid (pK$_a$ = 4.76) and sodium acetate. If the ratio of acetate to acetic acid is 10:1, what is the pH of the buffer?

Accepted Answer

$\mathrm{pH} = 4.76 + \log(10) = 5.76$

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

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