Q: What is the ion product of water ($$K_w) at 25$$°C?

$$K_w = 1.0 \times 10$$^{-14}$$

Question 1

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

Accepted Answer

Its high specific heat capacity

Question 2

Why does ice float on liquid water?

Accepted Answer

Ice has a lower density because its hydrogen bonds form an open lattice

Question 3

Which of the following best explains why water is an excellent solvent for ionic compounds?

Accepted Answer

Water molecules can form hydration shells around ions due to their permanent dipole

Question 4

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

Accepted Answer

$$pH = 4.76 + \log \frac{0.1}{0.01} = 4.76 + 1 = 5.76$$

Question 5

Which of the following statements about hydrogen bonds in biological systems is CORRECT?

Accepted Answer

Hydrogen bonds are critical for the specificity of biomolecular interactions

Question 6

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

Accepted Answer

Non-polar side chains cluster in the protein interior, increasing the entropy of water

Question 7

What is the ion product of water ($$K_w) at 25$$°C?

Accepted Answer

$$K_w = 1.0 	imes 10$$^{-14}$$

Question 8

A weak acid has a $$pK_a of 5.0. At $$what pH will the concentrations of the acid and its conjugate base be equal?

Accepted Answer

pH = 5.0

Question 9

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

Accepted Answer

Covalent disulfide bonds

Question 10

Which of the following statements about buffers is TRUE?

Accepted Answer

Buffers resist changes in pH when small amounts of acid or base are added

Question 11

A solution contains 50 mM acetate and 5 mM acetic acid. If the pH is 4.50, what is the $$pK_a of $$acetic acid? (Use the Henderson-Hasselbalch equation.)

Accepted Answer

$$pK_a = 4.50 - \log \frac{50}{5}$$

Question 12

Which of the following best explains why CO$$_2$$ and O$$_2$$ require specialized transport proteins in blood?

Accepted Answer

They are non-polar and have limited solubility in water

Question 13

Which of the following is a consequence of water's ability to form an average of 3.4 hydrogen bonds per molecule in liquid state?

Accepted Answer

Water has a high heat of vaporization

Question 14

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

Accepted Answer

It allows calculation of pH given $$pK_a$$ and the ratio of conjugate base to acid

Question 15

Which of the following best describes van der Waals interactions?

Accepted Answer

They are short-range, weak interactions between induced dipoles

Question 16

Which of the following is TRUE regarding the effect of water on ionic (electrostatic) interactions in biomolecules?

Accepted Answer

Water shields charged groups, reducing the strength of ionic interactions

Question 17

Which of the following is a key reason why the folding of a protein increases the entropy of water?

Accepted Answer

Folding buries non-polar groups, releasing ordered water molecules

Question 18

Which of the following is the correct formula for calculating pH from hydrogen ion concentration?

Accepted Answer

$$pH = -\log [H^+]$$

Question 19

Which of the following statements about homeopathy and water memory is supported by scientific evidence?

Accepted Answer

There is no substantial basis for the claim that water retains biological effectiveness at high dilution

Module 2: Water, Weak Interactions, and Buffers – Biochemistry Study Notes

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