Question 1

Which of the following best describes the role of pH in enzyme activity within a cell?

Accepted Answer

Enzyme activity is optimal at a specific pH, and deviations from this pH can decrease activity due to changes in enzyme structure.

Question 2

A solution contains a weak acid with a $pK_a$ of 4.8. If the concentration of the acid and its conjugate base are equal, what is the pH of the solution?

Accepted Answer

$pH = 4.8$

Question 3

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

Accepted Answer

$pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right)$

Question 4

A patient’s blood pH drops from 7.4 to 7.1. Which of the following best describes the physiological consequence?

Accepted Answer

The patient will experience acidosis, which can impair enzyme function and oxygen transport.

Question 5

If the $pK_a$ of lactic acid is 3.86, what is the ratio of lactate ($A^-$) to lactic acid ($HA$) in a solution with pH 5.0?

Accepted Answer

$\frac{[A^-]}{[HA]} = 13.8$

Question 6

Which of the following statements about buffer solutions is correct?

Accepted Answer

Buffers resist changes in pH when small amounts of acid or base are added.

Question 7

A biochemist prepares a buffer using acetic acid ($pK_a = 4.76$) and sodium acetate. If the final buffer has $[CH_3COOH] = 0.1$ M and $[CH_3COO^-] = 0.2$ M, what is the pH?

Accepted Answer

$pH = 5.06$

Question 8

Which of the following best explains why the bicarbonate buffer system is crucial in human blood?

Accepted Answer

It maintains blood pH by neutralizing excess acids and bases.

Question 9

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

Accepted Answer

$pH = 6$

Question 10

Which of the following scenarios would most likely result in metabolic alkalosis?

Accepted Answer

Excessive vomiting leading to loss of stomach acid.

Question 11

A buffer is prepared with equal concentrations of a weak acid and its conjugate base. If the $pK_a$ of the acid is 5.2, what is the pH of the buffer?

Accepted Answer

$pH = 5.2$

Question 12

Which of the following is the correct formula for calculating the $pK_a$ from the acid dissociation constant $K_a$?

Accepted Answer

$pK_a = -\log K_a$

Question 13

A researcher needs to prepare a buffer with a pH of 7.4 for a biochemical experiment. Which acid-base pair would be most suitable?

Accepted Answer

Tris base ($pK_a = 8.1$) and Tris-HCl

Question 14

Which of the following best describes the effect of adding a strong acid to a buffer solution?

Accepted Answer

The pH will decrease slightly, but the buffer will resist drastic changes.

Question 15

A solution contains $0.1$ M formic acid ($pK_a = 3.75$) and $0.1$ M sodium formate. What is the pH of the solution?

Accepted Answer

$pH = 3.75$

Question 16

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

Accepted Answer

Bicarbonate and carbonic acid in blood plasma

Question 17

A student adds $0.01$ mol of HCl to $1$ L of a buffer solution containing $0.1$ M acetic acid and $0.1$ M acetate. What will happen to the pH?

Accepted Answer

The pH will decrease slightly due to the buffer’s action.

Question 18

Which of the following is the correct relationship between $pH$, $pK_a$, and the ratio of conjugate base to acid in the Henderson-Hasselbalch equation?

Accepted Answer

$pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right)$

Question 19

A buffer solution is prepared with $[HA] = 0.05$ M and $[A^-] = 0.2$ M. If the $pK_a$ of the acid is 4.5, what is the pH of the buffer?

Accepted Answer

$pH = 5.2$

Acid-Base Chemistry: Calculating pH and pKa in Biochemistry

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