๐ฅ Strong Acids & Bases: pH & pOH
Unit 8 | Topic 3 – Strong Electrolytes in Solution
๐งช Strong Acids
- Strong acids are typically monoprotic and fully ionize in water.
- Examples: HCl and HNO₃.
- They produce a high concentration of H⁺/H₃O⁺ ions → low pH.
- The hydrogen ion concentration equals the acid’s molarity:
[H⁺] = Macid
pH = –log [H⁺]
The reaction goes fully to the right → treated as irreversible.
Diagram note: Strong acids show complete dissociation in water.
๐งผ Strong Bases
- Strong bases, such as Group 1 hydroxides, fully dissociate in water.
- Result: High concentration of OH⁻ ions → high pH.
- Some like Ba(OH)₂ release more than one OH⁻ per unit.
[OH⁻] = Mbase × #OH⁻ ions per mole
pOH = –log [OH⁻]
pH = 14 – pOH
Diagram note: Strong bases also show complete dissociation → irreversible process.
✅ Worked Examples
Example 1: Calculate the pH of a solution with a hydrogen ion concentration of 2.5 × 10⁻⁴ M.
pH = –log [H⁺] = –log(2.5 × 10⁻⁴) = 3.60
Example 2: Calculate the pH of a 0.00065 M solution of Ba(OH)₂.
- Each unit of Ba(OH)₂ releases 2 OH⁻ ions:
[OH⁻] = 0.00065 × 2 = 0.00130 M
pOH = –log(0.00130) = 2.89
pH = 14 – 2.89 = 11.11
๐ก AP Tip: Strong acids and bases are 100% dissociated — always use full molarity in your calculations. No need to use ICE tables!
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