1991 Chem MC (2)

2008-04-10 12:53 am

Which of the following processes would produce nitrogen dioxide?
(1)the action of heat on calcium nitrate
(2)the action of heat on ammonium nitrate
(3)the action of concentrated nitric acid on zinc

A.(1),(2)
B.(1),(3)
C.(2),(3)
D.(1),(2),(3)

Please explain briefly.

回答 (1)

Uncle Michael

2008-04-10 1:41 am

✔ 最佳答案

The answer is B.

(1) is correct.
When calcium nitrate is heated, it is decomposed to give calcium oxide, nitrogen dioxide and oxygen gas.
2Ca(NO3)2(s) → 2CaO(s) + 4NO2(g) + O2(g)

(2) is incorrect.
When ammonium nitrate is heated, it is decomposed to give dinitrogen oxide (not nitrogen dioxide) and water vapour.
NH4NO3 → N2O(g) + H2O(g)

(3) is incorrect.
Concentrated nitric acid is a strong oxidizing agent, which can oxidized zinc to zinc ions, and the concentrated nitric acid is reduced to nitrogen dioxide.
Zn(s) + 4H+(aq) + 2NO3-(aq) → Zn2+(aq) + 2H2O(l) + 2NO2(g)
or Zn(s) + 4HNO3(aq) → Zn(NO3)2(aq) + 2H2O(l) + 2NO2(g)

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