Question 1

Which property of water is primarily responsible for its ability to moderate Earth's climate and maintain stable temperatures in living organisms?

Accepted Answer

Its high heat capacity

Question 2

Why does water have a permanent dipole moment?

Accepted Answer

Because the O-H bonds are polar and the molecule is bent at 104.5°

Question 3

Which of the following best explains why ammonia (NH3) is highly soluble in water?

Accepted Answer

Ammonia is polar and forms hydrogen bonds with water

Question 4

Which of the following molecules would be LEAST soluble in water?

Accepted Answer

Hexanol (C6H13OH)

Question 5

What is the main reason that ice floats on liquid water?

Accepted Answer

Hydrogen bonds in ice form an open hexagonal lattice, making it less dense than liquid water

Question 6

Which of the following best describes the hydrophobic effect?

Accepted Answer

The aggregation of nonpolar molecules in water to minimize their exposure to the polar solvent

Question 7

A solution contains 0.1 M acetic acid and 0.5 M sodium acetate. If the pKa of acetic acid is 4.76, what is the pH of the solution? (Use the Henderson-Hasselbalch equation: $$pH = pK_a + \log \frac{[A^-]}{[HA]})$$

Accepted Answer

$$pH = 4.76 + \log \frac{0.5}{0.1} = 4.76 + 0.70 = 5.46$$

Question 8

Which of the following statements about hydrogen bonds in biological macromolecules is TRUE?

Accepted Answer

Hydrogen bonds are most stable when shielded from water, such as in the interior of proteins or DNA

Question 9

Which of the following is a correct statement about the isoelectric point (pI) of an amino acid?

Accepted Answer

It is the pH at which the amino acid has no net charge

Question 10

Which of the following best explains why sodium chloride (NaCl) dissolves readily in water?

Accepted Answer

Water molecules surround and stabilize the ions through ion-dipole interactions, weakening the ionic lattice

Question 11

Which of the following is NOT a property of acids?

Accepted Answer

Soapy feel

Question 12

A buffer solution is most effective at resisting changes in pH when:

Accepted Answer

The pH is close to the pKa of the buffer

Question 13

Which of the following equations correctly represents the relationship between pH and hydronium ion concentration?

Accepted Answer

$$pH = -\log [H_3O^+]$$

Question 14

Which of the following is a consequence of the hydrophobic effect in biological systems?

Accepted Answer

Spontaneous folding of proteins and self-assembly of biological membranes

Question 15

Which of the following statements about van der Waals forces is TRUE?

Accepted Answer

They are weak intermolecular forces that are maximal at the sum of van der Waals radii

Question 16

A solution has a hydronium ion concentration of $$1 	imes 10$$^{-6}$$ M. What is its pH?

Accepted Answer

$$pH = -\log(1 	imes 10$$^{-6}$$) = 6$$

Question 17

Which of the following best describes the role of chaotropic agents such as urea in protein chemistry?

Accepted Answer

They decrease the hydrophobic effect and denature proteins by disrupting water structure

Question 18

Which of the following is a correct application of the Henderson-Hasselbalch equation for a buffer composed of 0.2 M lactic acid and 0.25 M sodium lactate, with a pKa of 3.9?

Accepted Answer

$$pH = 3.9 + \log \frac{0.25}{0.2} = 3.9 + 0.10 = 4.0$$

Question 19

Which of the following statements about the titration of glycine is TRUE?

Accepted Answer

The isoelectric point (pI) is the average of the pKa values of the carboxyl and amino groups

The Chemical Foundation of Life: Water, Acids, Bases, and Buffers

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