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Nitric(V)acid is one of the mineral acids .

There are three mineral acids;

                Nitric(V)acid

                Sulphuric(VI)acid

                Hydrochloric acid.

Mineral acids do not occur naturally but are prepared in a school laboratory and manufactured at industrial level.

Nitric(V)acid is prepared in a school laboratory from the reaction  of Concentrated sulphuric(VI)acid and potassium nitrate(V) below.

                        KNO₃(s) + H₂SO₄(l)           -> KHSO₄(s)  + HNO₃(l)

Sodium nitrate can also be used to prepare nitric(V)acid.

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An all glass apparatus /retort is used during the preparation of nitric (V) acid since hot concentrated nitric (V) acid vapour is highly corrosive and attacks rubber /cork apparatus if used. Concentrated nitric (V) acid is colourless but the prepared sample in the school laboratory appears yellow. Hot concentrated   nitric (V) acid decomposes to brown nitrogen (IV) oxide and Oxygen gases.

                4HNO₃(l/g)     -> 4NO₂(g)   + H₂O (l)  +O₂(g)

Once formed the brown nitrogen (IV) oxide dissolves in the acid forming a yellow solution

 When concentrated nitric (V) acid is heated, brown fumes are observed and a colourless gas that relights/rekindles glowing splint produced.

Hot concentrated   nitric (V) acid decomposes to water, brown nitrogen(IV)oxide  and Oxygen gases.

 Oxygen gas is not visible in the brown fumes of nitrogen (IV) oxide.

                4HNO₃(g)     -> 4NO₂(g)   + H₂O (l)  +O₂(g)

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(a) Observation

  (i)Colour changes from green to yellow.

  (ii)brown fumes /gas produced on the upper parts of the test tube.

Explanation

  Concentrated   nitric(V) acid is a powerful/strong oxidizing agent. It oxidizes  green Fe2+ ions in FeSO4 to yellow Fe3+ .The acid is reduced to colourless Nitrogen(II)oxide.

Chemical equation:

     6FeSO4(aq) + 3H2SO4 (aq) + 2HNO3(aq) -> 3Fe2(SO4) 3 (aq)+ 4H2O + 2NO(g)

Colourless  Nitrogen(II)oxide is rapidly further oxidized to brown Nitrogen(IV)oxide by atmospheric oxygen.

Chemical equation:

  2NO(g)   +  O(g)  ->  2NO2 (g)

  (colourless)  (brown)

(b) Observation

  (i)Yellow colour of sulphur fades .

  (ii)brown fumes /gas produced.

Explanation

  Concentrated   nitric(V) acid is a powerful/strong oxidizing agent.

 It oxidizes yellow sulphur to colourless concentrated sulphuric(VI)acid.

 The acid is reduced to brown Nitrogen(IV)oxide gas.

Chemical equation:

S(s)  + 6HNO3(l) -> 4NO2(g)   + H2O (l)  +H2SO4(l)

(c) Observation

(i) brown fumes /gas at the top of the beaker produced with zinc and copper.

(ii) blue solution formed with copper turnings 

(iii) colourless solution formed with Zinc granules/Magnesium ribbon

(iv) pop sound produced with magnesium

Explanation

Nitric (V) acid is a powerful/strong oxidizing agent.

It oxidizes hydrogen gas produced to water in the case of zinc hence no hydrogen gas produced..

The acid is reduced to brown Nitrogen (II) oxide gas which is further oxidised to nitrogen (IV) oxide by air at the top of the beaker.

Chemical equation:

3Cu(s)   +  8HNO3(l)    ->  2NO(g)   + 4H2O (l)   +  3 Cu(NO3) 2 (aq)

3Zn(s)   +  8HNO3(l)     ->  2NO2(g)   +  4H2O (l)   +   3Zn(NO3) 2 (aq)

Mg(s)  +  2HNO3(l)     ->  Mg(NO3) 2 (aq)     +   H2(g)