Q: Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right)$

Question 1

Which of the following best describes the function of a buffer in a biological system?

Accepted Answer

A buffer maintains a constant pH by neutralizing added acids or bases.

Question 2

Which equation is used to calculate the pH of a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[	ext{A}^-]}{[	ext{HA}]} ight)$

Question 3

A buffer is made by mixing acetic acid ($\mathrm{p}K_a = 4.76$) and sodium acetate. If the concentration of acetic acid is 0.10 M and sodium acetate is 0.20 M, what is the pH of the buffer?

Accepted Answer

$\mathrm{pH} = 5.06$

Question 4

Which statement about $\mathrm{p}K_a$ is correct?

Accepted Answer

$\mathrm{p}K_a$ is the negative logarithm of the acid dissociation constant ($K_a$).

Question 5

Which amino acid has a nonpolar side chain and is represented by the 1-letter code 'L'?

Accepted Answer

Leucine

Question 6

Which of the following best describes the secondary structure of a protein?

Accepted Answer

The regular folding patterns such as $\alpha$-helices and $\beta$-sheets formed by hydrogen bonding between backbone atoms.

Question 7

Which amino acid is most likely to be found in the interior of a globular protein due to its hydrophobic side chain?

Accepted Answer

Valine

Question 8

A solution contains 0.10 M formic acid ($\mathrm{p}K_a = 3.75$) and 0.10 M sodium formate. What is the pH of the solution?

Accepted Answer

$\mathrm{pH} = 3.75$

Question 9

Which of the following changes will NOT significantly affect the pH of a buffer solution?

Accepted Answer

Adding a small amount of strong acid

Question 10

Which of the following is true about protein tertiary structure?

Accepted Answer

It is stabilized by interactions such as hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges.

Question 11

Which amino acid has a positively charged side chain at physiological pH and is represented by the 3-letter code 'Arg'?

Accepted Answer

Arginine

Question 12

At equilibrium, which of the following is true for a chemical reaction?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 13

Which equation represents the relationship between $K_a$ and $\mathrm{p}K_a$?

Accepted Answer

$\mathrm{p}K_a = -\log K_a$

Question 14

Which amino acid is most likely to participate in disulfide bond formation in proteins?

Accepted Answer

Cysteine

Question 15

Which of the following best describes the primary structure of a protein?

Accepted Answer

The linear sequence of amino acids in the polypeptide chain.

Question 16

A buffer solution is prepared with 0.25 M lactic acid ($\mathrm{p}K_a = 3.86$) and 0.10 M sodium lactate. What is the pH of the buffer?

Accepted Answer

$\mathrm{pH} = 3.44$

Question 17

Which amino acid is represented by the 1-letter code 'D' and has a negatively charged side chain at physiological pH?

Accepted Answer

Aspartic acid

Question 18

Which of the following is a property of glycine that distinguishes it from other amino acids?

Accepted Answer

It has no chiral center.

Question 19

Which of the following amino acids is aromatic and represented by the 3-letter code 'Phe'?

Accepted Answer

Phenylalanine

Question 20

Which of the following best explains why buffers are important in blood?

Accepted Answer

Buffers help maintain a stable pH, which is critical for enzyme function and metabolic processes.

Key Concepts in Buffers, Amino Acids, and Protein Structure

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