Which statement is true about acid strength and pKa in relation to strong and weak acids?

• A. Strong acids have a low pKa
• B. Strong acids have a high pKa
• C. pKa is independent of acid strength
• D. Weak acids have a low pKa

Answer: (A)

pKa and acid strength are inversely related: a stronger acid donates protons more readily, which means a larger Ka and therefore a smaller pKa. Since pKa is defined as the negative logarithm of Ka, increasing dissociation (larger Ka) drives pKa down. That’s why strong acids have low pKa values.

This is the best answer because it directly ties the concept to how pKa is computed and what it implies about proton donation in solution. The idea that pKa is independent of acid strength isn’t correct, and weak acids correspond to higher pKa values, not low ones.