Strong Acids & Bases
Related Examples and Practice Problems
Topic Summary & Highlights
and Help Videos
Core Concept
Strong Acids: Acids that completely dissociate into their ions in aqueous solution.
Example: HCl dissociates completely into ${H}^+$ and ${Cl}^−$. $$\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$$
Strong Bases: Bases that completely dissociate into their ions in aqueous solution.
Example: NaOH dissociates completely into ${Na}^+$ and ${OH}^−$. $$\text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^-$$
Practice Tips
Strong acids and bases dissociate completely in water, resulting in high ion concentrations.
The pH of strong acids is very low (≈0−1), while the pH of strong bases is very high (≈13−14).
Memorize common examples of strong acids and bases to identify them easily in chemical reactions.
Key Properties of Strong Acids and Bases
Strong Acids:
Complete Ionization: Strong acids release all of their hydrogen ions ($H^+$) into the solution.
High Conductivity: Due to complete dissociation, they produce a high concentration of ions, making the solution a good conductor of electricity.
High Reactivity: Strong acids react vigorously with metals, bases, and other compounds.
Strong Bases:
Complete Dissociation: Strong bases release all of their hydroxide ions (${OH}^−$) into the solution.
High Conductivity: The high concentration of ions results in excellent electrical conductivity.
High Reactivity: Strong bases react strongly with acids, amphiprotic substances, and organic compounds (e.g., saponification).
Particle Level Diagram
Strong Acid
What the Diagram Shows:
In the particle-level representation of a strong acid (e.g., HCl), you will see:
A mixture of free ions: $\text{H}_3\text{O}^+$ (or $\text{H}^+$) and the conjugate base (e.g., $\text{Cl}^-$).
No intact acid molecules because they have all dissociated.
The solution is highly ionic, with a large concentration of $\text{H}_3\text{O}^+$, which makes it highly conductive.
Weak Acid
What the Diagram Shows:
In the particle-level representation of a weak acid (e.g., CH₃COOH):
A mix of intact acid molecules and a few dissociated ions ($\text{H}_3\text{O}^+$ and $\text{CH}_3\text{COO}^-$).
The majority of particles are undissociated acid molecules.
The solution has a much lower concentration of ions compared to a strong acid, making it less conductive.
List of Strong Acids and Bases
There are 6 Strong Acids
| Acid | Formula |
|---|---|
| Hydrochloric acid | HCl |
| Nitric acid | HNO3 |
| Sulfuric acid | H2SO4 |
| Perchloric acid | HClO4 |
| Hydrobromic acid | HBr |
| Hydroiodic acid | HI |
It is common that students are expected to MEMORIZE the strong acids. (Double check with your teacher.) Here is a way that can help you memorize:
"So I Bring No Clean Clothes"
Where each word corresponds to one of the strong acids:
So → H₂SO₄ (Sulfuric acid)
I → HI (Hydroiodic acid)
Bring → HBr (Hydrobromic acid)
No → HNO₃ (Nitric acid)
Clean → HCl (Hydrochloric acid)
Clothes → HClO₄ (Perchloric acid)
Strong Bases (Group I & II hydroxides)
The common ones are below:
| Base | Formula |
|---|---|
| Sodium hydroxide | NaOH |
| Potassium hydroxide | KOH |
| Calcium hydroxide | Ca(OH)2 |
| Barium hydroxide | Ba(OH)2 |
| Lithium hydroxide | LiOH |