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JAMB Chemistry 1989 Question 30

Question 30

Nitrogen and its Compounds

Which of the following represents the balanced equation for the reaction of copper with concentrated trioxonitrate (V) acid?

  1. A.Cu(s) + 2HNO3(aq) → Cu(NO3)2(aq) + H2(g)
  2. B.Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2H2O(l) + 2NO2(g)
  3. C.3Cu(s) + 8HNO3(aq) → 3Cu(NO3)2(aq) + 4H2O(l) + 2NO(g)
  4. D.3Cu(s) + 4HNO3(aq) → 3Cu(NO3)2(aq) + 2H2O(l) + 2NO(g).
Show the answer and explanation

Answer: B (Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2H2O(l) + 2NO2(g))

Explanation

Concentrated HNO3 is reduced to brown nitrogen (IV) oxide: Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2. Option C is for dilute acid, and D is not balanced.