Question 1

A plasma pH of 6.8 does not seem too far away from a normal pH of 7.4.How many times greater is the H⁺ concentration at pH 6.8 compared to pH 7.4?

Accepted Answer

The pH scale is logarithmic, so each whole number change represents a tenfold change in H⁺ concentration. The difference between pH 7.4 and 6.8 is 0.6, which means the H⁺ concentration is 10^0.6 times greater, approximately 4 times greater.

Question 2

Which of the following values is the pKa for a weak acid that is 25% deprotonated at pH 4?

Accepted Answer

When a weak acid is 25% deprotonated, this means that the concentration of the conjugate base is equal to 25% of the initial concentration of the acid. Therefore, [A-]/[HA] = 0.25.
We also know that pH = pKa + log([A-]/[HA])
Plugging in the values we have, we get 4 = pKa + log(0.25)
Solving for pKa, we get pKa = 4.48. Therefore, the correct answer is C.

Question 3

At what pH are buffer systems most effective?

Accepted Answer

Buffer systems are most effective within 1 pH unit of the pKa value of the acid component of the buffer. This is because at this range, the buffer can effectively resist changes in pH by either donating or accepting protons.

Question 4

We are preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKₐ = 4.8)and sodium acetate.Which of the following should the volume of acetic acid be compared to the volume of sodium acetate solution?

Accepted Answer

To prepare an acetate buffer, the ratio of the concentration of the acid and its conjugate base should be between 1:1 and 10:1. Since the pKa of acetic acid (4.8) is close to the desired pH of the buffer (4.5), the buffer will be most effective if the concentration of the acid and its conjugate base are approximately equal (i.e., in a 1:1 ratio). Therefore, the volume of acetic acid should be about twice the volume of the sodium acetate solution. Hence, the correct answer is D.

Question 5

Which of the following is the purpose of the physiological mechanism of hyperventilation?

Accepted Answer

The purpose of hyperventilation is to increase the rate and depth of breathing, leading to the elimination of more carbon dioxide (CO₂) from the body. This results in a decrease in [CO₂ (g)] in the blood, which in turn causes an increase in blood pH. Therefore, choice A is the correct answer.

Question 6

Hypoventilation is characterized by inability to excrete CO₂ rapidly enough.Which of the following is NOT a cause of hypoventilation?

Accepted Answer

Encephalitis is an inflammation of the brain and is not directly related to respiratory function or hypoventilation. Therefore, it is not a cause of hypoventilation.

Question 7

The pKₐs of phosphoric acid are 2.1,7.2,and 12.Which of the following ionic form(s)of phosphoric acid is/are present at pH 7.0?

Accepted Answer

At pH 7.0, which is between the first and second pKₐ values, both H₂PO₄⁻ and HPO₄²⁻ are present in significant amounts.

Question 8

Which of the following characteristics does NOT apply to buffers?

Accepted Answer

Buffers have relatively flat titration curves at the pH(s) where they buffer, they resist changes in their pH as acid or base is added, and are typically composed of a weak acid and its conjugate base. However, buffers do not necessarily buffer best for polyprotic acids half-way between the 2 pKa values. The optimum pH range for buffering depends on the specific buffer system being used.

Question 9

Under which of these conditions does pH = pKₐ?

Accepted Answer

The answer of Under which of these conditions does pH...

Question 10

Which of the following buffer systems primarily maintain intracellular pH?

Accepted Answer

The buffer system that primarily maintains intracellular pH involves HPO₄- and H₂PO₄-, along with histidine. Histidine acts as a buffer when it accepts or donates protons to maintain a stable pH. Therefore, option D (HPO₄-/H₂PO₄-;histidine) is the best choice for the buffer system that primarily maintains intracellular pH.

Question 11

Which of the following will occur if an abundance of an organic acid with a pKa of 3.9 is found in the bloodstream?

Accepted Answer

The pH of the bloodstream is approximately 7.4, which is higher than the pKa of 3.9. Therefore, the organic acid will be mostly deprotonated in the bloodstream.

Question 12

The enzyme fumarase has a pH optimum of about 7.6.Which of the following would be the buffer of choice to study this enzyme?

Accepted Answer

Tris-hydroxymethyl aminomethane has a pKa of 8.07, which is close to the pH optimum of fumarase (7.6), making it an ideal buffer to study the enzyme's activity. Bicarbonate has a pKa of 10.24, which is too high for the pH range of interest, while lactic acid and acetic acid have pKa values that are too low.

Question 13

Aspirin contains a carboxylic acid with a pK_a of 3.5.Which of the following regarding its structure is correct?

Accepted Answer

Aspirin is a weak acid, so it will be mostly protonated in the stomach, where the pH is low.

Question 14

Water is particularly suited as a solvent for biosystems.Which of the following is NOT a characteristic of water?

Accepted Answer

Water is actually an excellent solvent for polar substances, due to its polarity and ability to form hydrogen bonds with other polar molecules. Non-polar substances, on the other hand, do not dissolve well in water. Therefore, choice C is not a characteristic of water.

Question 15

Which of the following weak acids would make the best buffer at pH = 5.0?

Accepted Answer

A good buffer should have a pKa value close to the target pH, which is 5.0 in this case. The closer the pKa value to the pH, the better the buffer capacity. Among the options given, acetic acid has the closest pKa value to 5.0 (pKa = 4.76), making it the best choice for a buffer at pH 5.0.

Quiz 2: Water: the Medium of Life

A plasma pH of 6.8 does not seem too far away from a normal pH of 7.4.How many times greater is the H⁺ concentration at pH 6.8 compared to pH 7.4?

Which of the following values is the pKa for a weak acid that is 25% deprotonated at pH 4?

At what pH are buffer systems most effective?

We are preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKₐ = 4.8) and sodium acetate.Which of the following should the volume of acetic acid be compared to the volume of sodium acetate solution?

Which of the following is the purpose of the physiological mechanism of hyperventilation?

Hypoventilation is characterized by inability to excrete CO₂ rapidly enough.Which of the following is NOT a cause of hypoventilation?

The pKₐs of phosphoric acid are 2.1,7.2,and 12.Which of the following ionic form(s) of phosphoric acid is/are present at pH 7.0?

Which of the following characteristics does NOT apply to buffers?

Under which of these conditions does pH = pKₐ?

Which of the following buffer systems primarily maintain intracellular pH?

Which of the following will occur if an abundance of an organic acid with a pKa of 3.9 is found in the bloodstream?

The enzyme fumarase has a pH optimum of about 7.6.Which of the following would be the buffer of choice to study this enzyme?

Aspirin contains a carboxylic acid with a pK_a of 3.5.Which of the following regarding its structure is correct?

Water is particularly suited as a solvent for biosystems.Which of the following is NOT a characteristic of water?

Which of the following weak acids would make the best buffer at pH = 5.0?

Quiz 2: Water: the Medium of Life

A plasma pH of 6.8 does not seem too far away from a normal pH of 7.4.How many times greater is the H⁺ concentration at pH 6.8 compared to pH 7.4?

Which of the following values is the pKa for a weak acid that is 25% deprotonated at pH 4?

At what pH are buffer systems most effective?

We are preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKₐ = 4.8) and sodium acetate.Which of the following should the volume of acetic acid be compared to the volume of sodium acetate solution?

Which of the following is the purpose of the physiological mechanism of hyperventilation?

Hypoventilation is characterized by inability to excrete CO₂ rapidly enough.Which of the following is NOT a cause of hypoventilation?

The pKₐs of phosphoric acid are 2.1,7.2,and 12.Which of the following ionic form(s) of phosphoric acid is/are present at pH 7.0?

Which of the following characteristics does NOT apply to buffers?

Under which of these conditions does pH = pKₐ?

Which of the following buffer systems primarily maintain intracellular pH?

Which of the following will occur if an abundance of an organic acid with a pKa of 3.9 is found in the bloodstream?

The enzyme fumarase has a pH optimum of about 7.6.Which of the following would be the buffer of choice to study this enzyme?

Aspirin contains a carboxylic acid with a pKa of 3.5.Which of the following regarding its structure is correct?

Water is particularly suited as a solvent for biosystems.Which of the following is NOT a characteristic of water?

Which of the following weak acids would make the best buffer at pH = 5.0?

Aspirin contains a carboxylic acid with a pK_a of 3.5.Which of the following regarding its structure is correct?