Q: If a certain acid has a $K_a$ of $5.0 \times 10^{-4}$, what is its $pK_a$?

$pK_a = -\log(5.0 \times 10^{-4}) = 3.30$

Question 1

Which statement best describes the difference between conformation and configuration in molecules?

Accepted Answer

Conformation refers to different arrangements of atoms in a molecule that can readily interconvert, while configuration refers to arrangements that cannot readily interconvert without breaking covalent bonds.

Question 2

Which of the following bonds is the strongest in biological systems?

Accepted Answer

Covalent bond

Question 3

A molecule with the formula $C_4H_{10}$ can exist as butane or isobutane. These are examples of:

Accepted Answer

Constitutional isomers

Question 4

Which of the following statements about water is TRUE?

Accepted Answer

Water has a dipole moment due to unequal electron sharing between hydrogen and oxygen.

Question 5

Which of the following best explains the hydrophobic effect?

Accepted Answer

It is the exclusion and clustering of nonpolar molecules in water, increasing hydrogen bonding among water molecules.

Question 6

According to the First Law of Thermodynamics, which of the following is TRUE?

Accepted Answer

Energy can change form but the total energy in the universe remains constant.

Question 7

A weak acid (HA) has a $pK_a$ of 4.5. If the pH of the solution is 6.5, what is the predominant form present?

Accepted Answer

Mostly A- (deprotonated form)

Question 8

Which of the following statements about enantiomers is CORRECT?

Accepted Answer

Enantiomers have identical physical properties except for their interaction with plane-polarized light and chiral environments.

Question 9

Which of the following is the correct formula for calculating the pH of a solution given the hydrogen ion concentration?

Accepted Answer

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

Question 10

A buffer is most effective when:

Accepted Answer

The pH of the solution is equal to the pKa of the buffer.

Question 11

Which of the following statements about the Second Law of Thermodynamics is TRUE?

Accepted Answer

Spontaneous processes increase the disorder (entropy) of the universe.

Question 12

If a certain acid has a $K_a$ of $5.0 	imes 10^{-4}$, what is its $pK_a$?

Accepted Answer

$pK_a = -\log(5.0 	imes 10^{-4}) = 3.30$

Question 13

Which of the following is a property of amphipathic molecules?

Accepted Answer

They contain both polar and nonpolar components.

Question 14

Which of the following is TRUE regarding the physiological significance of a drug with two enantiomers?

Accepted Answer

One enantiomer may bind specifically to a target receptor, while the other may not fit and have different effects.

Question 15

Which of the following statements about the hydrophobic effect and protein folding is CORRECT?

Accepted Answer

The hydrophobic effect drives nonpolar amino acids to the interior of proteins, away from water.

Question 16

Which of the following is NOT a type of noncovalent interaction important in biochemistry?

Accepted Answer

Covalent bond

Question 17

Which of the following statements about buffer regions is TRUE?

Accepted Answer

Buffering occurs at pH values one unit above and below the pKa.

Question 18

Which of the following is a correct statement about polar molecules?

Accepted Answer

Polar molecules have an uneven distribution of charge.

Question 19

Which of the following is TRUE regarding the relationship between pH and pKa for a weak acid?

Accepted Answer

When pH > pKa, the acid is mostly deprotonated.

Biochemistry Exam 1 Study Guide: Foundations of Molecular Structure, Water, Thermodynamics, and Acid-Base Chemistry

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