U8.2 · pH and pOH of Strong Acids and BasesPractice · 强酸强碱的 pH 与 pOH
Lessons covered:U8.2 pH and pOH of Strong Acids and Bases
- 1Numeric
What is the pH of 0.0025 M Sr(OH)₂ at 25 °C?
ExplanationSr(OH)₂ is a strong base that ionizes completely, giving 2 OH⁻ each: [OH⁻] = 2 × 0.0025 = 0.0050 M, pOH = 2.30, pH = 11.70. Forgetting the 2 gives 11.40.
- 2Select all
Which of these are strong acids or strong bases? Select all that apply.
More than one option may be correct. Choose all that apply, then press Submit.
ExplanationCommon strong acids: HCl, HBr, HI, HNO₃, HClO₄, and H₂SO₄ (first ionization). Common strong bases: the Group 1 hydroxides plus Ca(OH)₂, Sr(OH)₂, and Ba(OH)₂. HF is a weak acid (its H–F bond is very strong), and so are H₂CO₃ and CH₃COOH.
- 3Numeric
10.0 mL of hydrochloric acid at pH 1.20 is diluted with water to 500.0 mL. What is the pH after dilution?
ExplanationThe volume grows 50-fold, so [H⁺] falls to 1/50 and the pH rises by log 50 = 1.70: 1.20 + 1.70 = 2.90. Or compute [H⁺] = 10−1.20 = 0.0631 M first and divide by 50.
- 4Numeric
25.0 mL of 0.120 M HNO₃ is mixed with 35.0 mL of 0.080 M KOH. What is the pH of the mixture?
Explanationn(H⁺) = 25.0 × 0.120 = 3.00 mmol and n(OH⁻) = 35.0 × 0.080 = 2.80 mmol. H⁺ is in excess by 0.20 mmol; dividing by the total volume of 60.0 mL gives [H⁺] = 3.33 × 10−3 M and pH = 2.48. Remember to use the combined volume.
- 5Multiple choice
Equal volumes of hydrochloric acid at pH 2.00 and NaOH solution at pH 12.00 are mixed at 25 °C. What is the pH of the mixture?
ExplanationAt pH 2.00, [H⁺] = 0.010 M; at pH 12.00, [OH⁻] = 10−2.00 = 0.010 M. With equal volumes, the moles of H⁺ and OH⁻ are equal and exactly neutralize, and the NaCl formed doesn’t affect the pH, so pH = 7.00.
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