The pH of a solution is 5. The hydroxyl ion concentration in mol·dm⁻³ is:

Correct answer: B. 10⁻⁹

  • A. 10⁻⁵
  • B. 10⁻⁹
  • C. 10⁵⋅⁵
  • D. 10⁻⁷

Explanation

The relationship between pH and pOH is pH + pOH = 14. If the pH is 5, the pOH is 14 - 5 = 9. The hydroxyl ion concentration is [OH⁻] = 10⁻pOH = 10⁻⁹ M.

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About Acids, Bases and Salts

Acid and base behaviour is explained through the Bronsted-Lowry transfer of protons and the Lewis donation or acceptance of electron pairs. The topic includes pH, pOH, ionisation and water equilibrium, plus salt formation and hydrolysis, where a salt solution may become acidic, basic or neutral.

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