Q: A solution contains a weak acid, HA, and its conjugate base, A-. If the concentration of HA is 0.1 M and the concentration of A- is 0.2 M, and the pKa of HA is 5.0, what is the pH of the solution? Use the Henderson-Hasselbalch equation.

$\text{pH} = 5.0 + \log_{10} \left( \frac{0.2}{0.1} \right) = 5.0 + 0.301 = 5.3$

Q: A buffer is prepared using acetic acid (pKa = 4.76) and sodium acetate. What is the effective buffering range for this buffer?

$3.76 \leq \text{pH} \leq 5.76$

Q: Which of the following equations correctly relates pH, pKa, and the ratio of conjugate base to acid in a buffer system?

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

Question 1

Which of the following best describes why life is thermodynamically possible on Earth, according to the laws of thermodynamics?

Accepted Answer

Because the formation of biomolecules increases the local order, but the overall disorder of the universe increases.

Question 2

A solution contains a weak acid, HA, and its conjugate base, A-. If the concentration of HA is 0.1 M and the concentration of A- is 0.2 M, and the pKa of HA is 5.0, what is the pH of the solution? Use the Henderson-Hasselbalch equation.

Accepted Answer

$	ext{pH} = 5.0 + \log_{10} \left( \frac{0.2}{0.1} ight) = 5.0 + 0.301 = 5.3$

Question 3

Which of the following functional groups is NOT commonly found in biological molecules?

Accepted Answer

Nitro group ($-\mathrm{NO}_2$)

Question 4

The Miller-Urey experiment demonstrated that:

Accepted Answer

A mixture of simple gases and an electrical discharge can produce organic molecules such as amino acids.

Question 5

Which of the following statements about water is FALSE?

Accepted Answer

Water is a good solvent for nonpolar molecules.

Question 6

A buffer is prepared using acetic acid (pKa = 4.76) and sodium acetate. What is the effective buffering range for this buffer?

Accepted Answer

$3.76 \leq 	ext{pH} \leq 5.76$

Question 7

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

Accepted Answer

They maintain a relatively constant pH, which is critical for the function of biomolecules.

Question 8

Given the following reaction: $\mathrm{HA} \rightleftharpoons \mathrm{H}^+ + \mathrm{A}^-$, the acid dissociation constant ($K_a$) is defined as:

Accepted Answer

$K_a = \frac{[\mathrm{H}^+][\mathrm{A}^-]}{[\mathrm{HA}]}$

Question 9

A patient is experiencing metabolic acidosis. Which of the following is a likely cause?

Accepted Answer

Increased acid production in the body

Question 10

Which of the following equations correctly relates pH, pKa, and the ratio of conjugate base to acid in a buffer system?

Accepted Answer

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

Question 11

Which of the following best describes the role of the carbonic acid buffer system in blood?

Accepted Answer

It maintains blood pH by balancing the concentrations of HCO$_3^-$ and CO$_2$.

Question 12

If the partial pressure of CO$_2$ ($pCO_2$) in arterial blood increases, what is the expected effect on blood pH according to the Henderson-Hasselbalch equation for the carbonic acid buffer system?

Accepted Answer

Blood pH will decrease.

Question 13

Which of the following is a correct statement about the first and second laws of thermodynamics as they apply to living systems?

Accepted Answer

Energy can be transformed in living systems, but not with 100% efficiency.

Question 14

Which of the following best explains why water is an excellent solvent for ionic and polar substances?

Accepted Answer

Water molecules can form hydrogen bonds and have a high dielectric constant.

Question 15

A solution has a pH of 8. What is the concentration of hydrogen ions $[\mathrm{H}^+]$ in the solution?

Accepted Answer

$[\mathrm{H}^+] = 1 	imes 10^{-8}~\mathrm{M}$

Question 16

Which of the following is a real-life example of a buffer system in the human body?

Accepted Answer

H$_2$CO$_3$ and HCO$_3^-$ in blood

Question 17

Which of the following best describes the effect of adding a strong base to a buffer solution containing a weak acid and its conjugate base?

Accepted Answer

The weak acid will react with the base, minimizing the change in pH.

Question 18

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

Accepted Answer

$	ext{pH} = -\log_{10} [\mathrm{H}^+]$

Question 19

A patient is hyperventilating. What acid-base disorder are they most likely to develop?

Accepted Answer

Respiratory alkalosis

Introduction to Biochemistry: Course Overview and Foundations

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