1. What is pKa?

pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution. It indicates the pH at which half of the acid molecules are dissociated. The pKa value is dimensionless.

2. How to Determine pKa from a Graph

The pKa can be determined from a titration curve by identifying the inflection point:

Steps:

1. Perform a titration and plot pH vs. volume of titrant
2. Identify the inflection point (steepest part of the curve)
3. The pH at this point equals the pKa

3. Importance of pKa Calculation

Details: pKa values are crucial in chemistry and biochemistry for understanding acid-base behavior, predicting molecular charge states, and designing pharmaceutical compounds.

4. Using the Calculator

Tips: Simply enter the pH value at the inflection point of your titration curve. The calculator will return the pKa value which is numerically equal to the pH at this point.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between pH and pKa?
A: pH measures the acidity of a solution, while pKa measures the inherent strength of an acid (its tendency to donate protons).

Q2: Can pKa be negative?
A: Yes, for very strong acids. Most biological acids have pKa values between 2-12.

Q3: How does temperature affect pKa?
A: pKa values are temperature-dependent. Most tables report values at 25°C.

Q4: What if my titration curve has multiple inflection points?
A: This indicates multiple ionizable groups, each with its own pKa value.

Q5: How accurate is this method?
A: For monoprotic acids, very accurate. For polyprotic acids, more complex analysis is needed.