Q: Which of the following equations correctly represents the ion product of water at 25°C?

$$K_w = [H^+][OH^-] = 1.0 \times 10$$^{-14}$$~M^2$

Question 1

Which property of water is primarily responsible for its ability to moderate temperature in living organisms?

Accepted Answer

Its high specific heat capacity

Question 2

A protein folds so that its hydrophobic amino acid side chains are buried in the interior, away from water. Which thermodynamic principle best explains this phenomenon?

Accepted Answer

The increase in entropy of water molecules released from hydrophobic surfaces

Question 3

Which of the following best describes the geometry and strength of hydrogen bonds in anti-parallel versus parallel beta sheets?

Accepted Answer

Hydrogen bonds in anti-parallel beta sheets are more stable due to optimal geometry

Question 4

Which of the following equations correctly represents the ion product of water at 25°C?

Accepted Answer

$$K_w = [H^+][OH^-] = 1.0 	imes 10$$^{-14}$$~M^2$

Question 5

A solution contains 0.01 M acetic acid and 0.1 M sodium acetate. If the pKa of acetic acid is 4.76, what is the pH of the solution? (Use the Henderson-Hasselbalch equation.)

Accepted Answer

pH = 4.76 + log(0.1/0.01) = 5.76

Question 6

Which of the following statements about water's role as a solvent is correct?

Accepted Answer

Water's permanent dipole allows it to form hydration shells around ions

Question 7

Which of the following best explains why ice floats on liquid water?

Accepted Answer

Ice has a lower density because its hydrogen bonds create an open, ordered lattice

Question 8

Which of the following is NOT a type of non-covalent interaction important in biomolecular structure?

Accepted Answer

Peptide bonds

Question 9

A weak acid, HA, has a pKa of 5.0. At what pH will the concentrations of HA and its conjugate base A$$^- be $$equal?

Accepted Answer

pH = 5.0

Question 10

Which of the following best describes the effect of water on ionic (electrostatic) interactions between biomolecules?

Accepted Answer

Water shields charged groups, diminishing the strength of ionic interactions

Question 11

Which of the following statements about the Henderson-Hasselbalch equation is correct?

Accepted Answer

It relates pH, pKa, and the ratio of base to acid concentrations

Question 12

Which of the following is a real-world example of a biological buffer system?

Accepted Answer

The bicarbonate buffer system in blood

Question 13

Which of the following best explains why most biomolecules are amphipathic?

Accepted Answer

They contain both hydrophilic and hydrophobic regions

Question 14

A solution is prepared by mixing 5 mM lactic acid and 50 mM lactate. If the pH is 4.80, what is the pKa of lactic acid?

Accepted Answer

pKa = 4.80 - log(50/5) = 3.80

Question 15

Which of the following statements about van der Waals interactions is correct?

Accepted Answer

They are short-range, weak interactions between permanent and induced dipoles

Question 16

Which of the following best describes the effect of the hydrophobic effect on protein folding?

Accepted Answer

It drives non-polar side chains to the protein interior, increasing water entropy

Question 17

Which of the following is a consequence of water's ability to form four hydrogen bonds per molecule?

Accepted Answer

Water has a high heat of vaporization and specific heat capacity

Question 18

Which of the following statements about the pH scale is correct?

Accepted Answer

A difference of 1 pH unit corresponds to a 10-fold difference in [H$$^+$$]

Question 19

Which of the following is a correct statement about the role of buffers in biological systems?

Accepted Answer

Buffers minimize changes in pH upon addition of small amounts of acid or base

Water, Weak Interactions, and Buffers: Structure, Properties, and Biological Importance

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