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Related Topic: Nitrogen and its Compounds

Related Subtopic: Action of heat on nitrates



Questions 4.6.1

  1. State and explain the common observations when nitrates are heated.
  2. Which observations apply to nitrates of heavy metals (e.g. copper, zinc, and lead) only?
  3. How does the observation with ammonium nitrate differ from that of other nitrates?
  4. Write equations for thermal decomposition of each of the following nitrates.
    1. Sodium nitrate (NaNO3)
    2. Potassium nitrate (KNO3)
    3. Ammonium nitrate (NH4NO3)
    4. Copper (II) nitrate (Cu(NO3)2)
    5. Zinc nitrate (Zn(NO3)2)
    6. Lead (II) nitrate (Pb(NO3)2)
    7. Silver nitrate (AgNO3) NB: Hot silver oxide is unstable and readily decomposes to silver metal and oxygen gas.
    8. Mercury (II) nitrate (Hg(NO3)2)
  5. While heating a salt, when should we begin to suspect that it is a nitrate?


Answers to Questions 4.6.1


  1. A colourless odourless and neutral gas that relights a glowing splint, and a solid residue, except for ammonium nitrate. The gas is oxygen, and the solid residue is metal oxide (for heavy metls) and nitrites for light metals, both produced as the nitrates thermally decompose.
  2. A brown-red gas that turns wet blue litmus red.
  3. Production of a colourless, and neutral gas that has a faint sweet smell and relights a glowing splint. No solid residue is left.
  4. (a) 2NaNO3(s) → 2NaNO2(s) + O2(g)
    (b) 2KNO3(s) → 2KNO2(s) + O2(g)
    (c) NH4NO3(s) → 2H2O(g) + N2O(g)
    (d) 2Cu(NO3)2(s) → 2CuO(s) + 4NO2(g) + O2(g) not balanced
    (e) 2Zn(NO3)2(s) → 2ZnO(s) + 4NO2(g) + O2(g)
    (f) 2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)
    (g) 2AgNO3(s) → 2Ag(s) + 2NO2(g) + O2(g)
    5. (h) Hg(NO3)2(s) → Hg(l) + 2NO2(g) + O2(g)
  5. We begin to suspect a nitrate when the solid decomposes with a rattling sound and produces a brown-red acidic gas.