What is the relationship between pKa and Ka?

What is the relationship between pKa and Ka?

• A. Higher pKa indicates higher Ka
• B. Lower pKa indicates lower Ka
• C. pKa is directly proportional to Ka
• D. pKa is the negative log of Ka

Answer: (D)

The relationship between pKa and Ka lies in the definition of pKa, which is derived from the acid dissociation constant (Ka) of a given acid. Specifically, pKa is defined as the negative logarithm (base 10) of the Ka value: \[ \text{pKa} = -\log(\text{Ka}) \] This relationship indicates that as the Ka value increases, representing a stronger acid that dissociates more completely in solution, the pKa value decreases. Therefore, pKa provides an intuitive way to express the strength of an acid: a lower pKa signifies a stronger acid because it correlates to a higher Ka. The correct choice highlights this fundamental relationship, emphasizing the logarithmic relationship between the two values. Understanding this allows for better insight into acid-base equilibria, making it easier to compare the strengths of different acids.

The relationship between pKa and Ka lies in the definition of pKa, which is derived from the acid dissociation constant (Ka) of a given acid. Specifically, pKa is defined as the negative logarithm (base 10) of the Ka value:

[ \text{pKa} = -\log(\text{Ka}) ]

This relationship indicates that as the Ka value increases, representing a stronger acid that dissociates more completely in solution, the pKa value decreases. Therefore, pKa provides an intuitive way to express the strength of an acid: a lower pKa signifies a stronger acid because it correlates to a higher Ka.

The correct choice highlights this fundamental relationship, emphasizing the logarithmic relationship between the two values. Understanding this allows for better insight into acid-base equilibria, making it easier to compare the strengths of different acids.