Question

Which one is incorrect with regard to pK$_a$?

• A. In pK\(_a\), K\(_a\) is acid dissociation constant
• B. pK\(_a\) is measurement of the concentration of hydrogen ions in a solution
• C. Higher the K\(_a\) the stronger the acid
• D. pK\(_a\) is used to show the strength of an acid

Hint:

• \(K_a\): Acid dissociation constant. Larger \(K_a \implies\) stronger acid.
• pK\(_a = -\log_{10}K_a\). Smaller pK\(_a \implies\) stronger acid.
• pH = \(-\log_{10}[\text{H}^+]\). Measures hydrogen ion concentration (acidity/basicity of a solution).
• Henderson-Hasselbalch equation relates pH, pK\(_a\), and the ratio of conjugate base to acid: pH = pK\(_a\) + \(\log_{10}(\frac{[\text{A}^-]}{[\text{HA}]})\).

Answer 1

The Correct Option is B

The given question requires identifying which statement regarding pK_a is incorrect. To solve this, we must analyze the provided statements:

Statement Analysis:

• In pK_a, K_a is acid dissociation constant: This statement is correct. K_a represents the acid dissociation constant for a given acid.

• pK_a is measurement of the concentration of hydrogen ions in a solution: This statement is incorrect. pK_a is not a direct measurement of hydrogen ion concentration. It is a logarithmic scale that measures the strength of an acid by expressing the acid dissociation constant.

• Higher the K_a the stronger the acid: This statement is correct. A higher K_a indicates greater dissociation into ions, thus a stronger acid.

• pK_a is used to show the strength of an acid: This statement is correct. pK_a provides a measure of the acid's strength; lower pK_a means a stronger acid as it dissociates more completely.

Therefore, the incorrect statement among the options is: pK_a is measurement of the concentration of hydrogen ions in a solution.