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Related Topic: Nitrogen and its Compounds

Related Subtopic: Reactions of dilute nitric (V) acid



Questions 4.5.3

  1. State the observations made when very dilute nitric (V) acid (far below 2M) is reacted with magnesium metal.
  2. Write an equation for the reaction between very dilute nitric (V) acid and magnesium metal.
  3. State and explain the observations made when moderately dilute nitric (V) acid (2M) is added to separate samples of zinc and copper metals.
  4. Write chemical equations for the reactions that occur.
  5. Suggest a reason why copper metal reacts with dilute nitric (V) acid yet it is less reactive than hydrogen.

    6. Questions 6-9 are about reactions of nitric (V) acid, whether very dilute or moderately dilute.
    Complete the equations and explain the corresponding observations.

  6. CuO(s) + HNO3(aq)
  7. NaOH(aq) + HNO3(aq)
  8. CaCO3(s) + HNO3(aq)
  9. KHCO3(aq) + HNO3(aq)


Answers to Questions 4.5.3


  1. Vigorous effervescence occurs, producing bubbles of a colourless gas. A colourless solution is formed.
  2. 2HNO3(aq) + Mg(s) → Mg(NO3)2(aq) + H2(g)
  3. With zinc metal: Vigorous effervescence occurs, producing bubbles of a colourless gas which turns red-brown in air. A colourless solution is formed.
    With copper metal: Vigorous effervescence occurs, producing bubbles of a colourless gas which turns red-brown in air. A deep blue solution is formed.
  4. For zinc: 3Zn(s) + 8HNO3(aq) → 3Zn(NO3)2(aq) + 4H2O(l) + 2NO(g)
    For copper: 3Cu(s) + 8HNO3(aq) → 3Cu(NO3)2(aq) + 4H2O(l) + 2NO(g)
    NB: This is the usual laboratory preparation of nitrogen (II) oxide.
  5. Nitric (V) acts as an oxidizer and not typically as an acid; so hydrogen is not directly displaced by copper but instead oxidized to water.
  6. CuO(s) + 2HNO3(aq) → Cu(NO3)2(aq) + H2O(l)
    The black copper (II) oxide powder reacts with the acid to form a deep blue solution of copper (II) nitrate.
  7. NaOH(aq) + HNO3(aq) → NaNO3(aq) + H2O(l)
    The base and acid mutually neutralize each other to form sodium nitrate salt and water.
  8. CaCO3(s) + 2HNO3(aq) → Ca(NO3)2(aq) + H2O(l) + CO2(g)
    Vigorous effervescence is caused by production of the colourless carbon (IV) oxide gas as a colouless solution of calcium nitrate is formed.
  9. KHCO3(aq) + HNO3(aq) → KNO3(aq) + H2O(l) + CO2(g)
    Vigorous effervescence is caused by production of the colourless carbon (IV) oxide gas as a colouless solution of potassium nitrate is formed.

Very dilute nitric (V) acid (well below 2M) behaves typically as an acid by donating hydrogen ions (protons, H+), in which case hydrogen gas is one of the products. For example, it reacts with magnesium metal to produce hydrogen gas.


Moderately dilute nitric (V) acid behaves more as an oxidizer, donating oxygen as it is itself reduced to nitrogen (II) oxide (NO), than as an acid. Therefore, water and nitrogen (II) oxide are produced instead.


However, whether moderately dilute or very dilute, nitric acid reacts with bases (metal oxides and hydroxides), carbonates and hydrogencarbonates typically as an acid.