Strong Acids Memory Aid
HI! I Bring Clean Strong HNO3 And Super HClO4
Remember the six strong acids that completely dissociate in water: HI, HBr, HCl, HNO3, H2SO4, and HClO4. If an acid isn't on this list, it's weak and requires Ka calculations.
Breakdown
Hydroiodic acid
Strong acid, pKa = -10
Hydrobromic acid
Strong acid, pKa = -9
Hydrochloric acid
Strong acid, pKa = -7
Nitric acid
Strong acid, pKa = -1.4
Sulfuric acid
Strong acid (first H), pKa1 = -3
Perchloric acid
Strongest common acid, pKa = -10
Example
0.1 M HCl has [H+] = 0.1 M and pH = 1 (complete dissociation). But 0.1 M acetic acid (weak) has [H+] << 0.1 M because it only partially dissociates.
When to Use This
- ✓Calculating pH of acidic solutions
- ✓Determining if Ka calculation is needed
- ✓Predicting complete dissociation
- ✓Identifying conjugate base strength
FAQs
Common questions about this mnemonic
Despite fluorine's high electronegativity, the H-F bond is extremely strong (bond energy 568 kJ/mol). This strong bond makes it hard for HF to release H+, making it a weak acid.
Only the first proton of H2SO4 is strong. The second dissociation (HSO4- -> H+ + SO42-) has Ka2 = 0.012, making it weak. For most purposes, treat H2SO4 as donating two H+ though.