Unit 8: Topic 2 - pH and pOH of Strong Acids and Bases Flashcards
What are strong acids and how do we calculate the pH of a strong acid solution?
When dissolved in an aqueous solution, strong acids dissociate completely into ions (H₃O⁺ and an anion). The seven most common strong acids are hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI), chloric acid (HClO₃), perchloric acid (HClO₄), sulfuric acid (H₂SO₄), and nitric acid (HNO₃).
The concentration of H₃O⁺ in a strong acid solution is equal to the initial concentration of the strong acid, so given a strong acid HA, pH of a strong acid solution = -log[HA].
What is the pH and pOH of a 0.0235 M HCl solution?
pH = 1.63
pOH = 12.37
HCl + H₂O -> H₃O⁺ + Cl⁻
pH = -log[H₃O⁺] = -log[HCl] = -log[0.0235] = 1.63
pOH = 14 - pH = 14 - 1.63 = 12.37
What are strong bases and how do we calculate the pH of a strong base solution?
When dissolved in an aqueous solution, strong bases dissociate completely into ions (OH⁻ and a cation). Strong bases are group I and II hydroxides.
The concentration of OH⁻ in a strong base solution is equal to the initial concentration of the strong base, so given a strong base BOH, pOH of a strong base solution = -log[BOH].
What is the pH of a 0.00705 M Ca(OH)₂ solution?
pH = 11.85
Ca(OH)₂ + H₂O -> Ca²⁺ + 2OH⁻
pH = 14 - pOH = 14 - (-log[OH⁻]) = 14 - (-log[Ca(OH)₂ = 14 - (-log[0.00705]) = 14 - 2.15 = 11.85
