Acid/Base Strength
Strong acids ionize completely in water while weak acids ionize only partially, and the stronger the acid, the weaker its conjugate base. Ka and pKa put a number on that tendency; the pKa study guide covers the full framework.
Identify strong vs weak, compare strengths, and match conjugate pairs in the problems below.
Common Questions
What makes an acid strong vs. weak?
Strong acids (HCl, HBr, HI, HNO3, H2SO4, HClO4) completely dissociate in water — every molecule gives up its proton. Weak acids only partially dissociate, establishing an equilibrium between the acid and its conjugate base.
What makes a base strong vs. weak?
Strong bases (group 1 and 2 hydroxides like NaOH, KOH, Ca(OH)2) completely dissociate in water. Weak bases (like NH3 and organic amines) only partially accept protons, with most molecules remaining unprotonated.
What is a conjugate acid-base pair?
A conjugate pair differs by exactly one proton. When an acid donates H+, it becomes its conjugate base. When a base accepts H+, it becomes its conjugate acid. Example: HCl/Cl- and NH3/NH4+.
How are Ka and Kb related?
For a conjugate acid-base pair, Ka x Kb = Kw = 1.0 x 10^-14 at 25°C. A stronger acid (larger Ka) has a weaker conjugate base (smaller Kb), and vice versa.