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JAMB Chemistry 2002 Question 23

Question 23

Acids, Bases and Salts

Which of the following solutions containing only hydroxyl ions will liberate hydrogen gas when reacted with magnesium metal?

  1. A.1.0 × 10−6 mol dm−3
  2. B.1.0 × 10−12 mol dm−3
  3. C.1.0 × 10−2 mol dm−3
  4. D.1.0 × 10−4 mol dm−3
Show the answer and explanation

Answer: B (1.0 × 10−12 mol dm−3)

Explanation

Magnesium liberates hydrogen from acids. [OH−] = 10−12 means pOH = 12 and pH = 2, which is acidic. The other solutions have pH 8, 12 and 10 (alkaline).