Question

Among the metals Fe, Zn, Pb, Ag and Pt, which do not give a metal nitrate on treatment with concentrated ${\rm{HN}}{{\rm{O}}_{\rm{3}}}$?
A. Fe and Pt
B. Fe and Zn
C. Fe, Ag and Pt
D. Pb, Ag and Pt

Answer 1

Hint: Nitrogen forms oxoacids namely hyponitrous acid $\left( {{{\rm{H}}_{\rm{2}}}{{\rm{N}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}} \right)$ and nitrous acid $\left( {{\rm{HN}}{{\rm{O}}_{\rm{2}}}} \right)$ and nitric acid $\left( {{\rm{HN}}{{\rm{O}}_{\rm{3}}}} \right)$. Nitric acid is a colourless liquid. Nitric acid used in the laboratory has 68% ${\rm{HN}}{{\rm{O}}_{\rm{3}}}$ by mass and possess a specific gravity of 1.504. It behaves as strong acid in aqueous solution.

Complete step by step answer:
Let’s understand the reaction of nitric acid. It acts as strong oxidizing agents and attacks most metals except noble gases. The products formed depend on the acid concentration, nature and temperature of the substance undergoing the reaction.

When copper reacts with dilute nitric acid, copper nitrate, nitric oxide and water form.

 $3{\rm{Cu}} + 8{\rm{HN}}{{\rm{O}}_{\rm{3}}}\left( {dilute} \right) \to 3{\rm{Cu}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_2} + 2{\rm{NO}} + 4{{\rm{H}}_{\rm{2}}}{\rm{O}}$


Reaction of copper with nitric acid (dilute) produces copper nitrate, water and nitric oxide.

${\rm{Cu}} + 4{\rm{HN}}{{\rm{O}}_{\rm{3}}}\left( {conc.} \right) \to {\rm{Cu}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_2} + 2{\rm{N}}{{\rm{O}}_2} + 2{{\rm{H}}_{\rm{2}}}{\rm{O}}$


Now come to the question. We have to identify the metal which does not undergo reaction with concentrated nitric acid.

First metal is iron (Fe). Due to the reaction of iron with concentrated nitric acid, a protective layer of ${\rm{FeO}}.{\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}$ is formed on its surface which stops the reaction by preventing further oxidation reaction. So, iron will not undergo reaction with nitric acid.

Next metal is platinum (Pt). We know that noble metals like platinum and gold do not undergo reaction with nitric acid because they are inert in nature.

Next metal is zinc (Zn). Zinc reacts with concentrated nitric acid to form zinc nitrate, water and nitrogen dioxide.

${\rm{Zn}} + 4{\rm{HN}}{{\rm{O}}_{\rm{3}}}\left( {conc.} \right) \to {\rm{Zn}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_2} + 2{{\rm{H}}_{\rm{2}}}{\rm{O}} + 2{\rm{N}}{{\rm{O}}_{\rm{2}}}$


Next metal is silver (Ag). Reaction of silver with conc. nitric acid produces silver nitrate salt, water and nitrogen dioxide.

${\rm{3Ag}} + 4{\rm{HN}}{{\rm{O}}_{\rm{3}}}\left( {{\rm{conc}}{\rm{.}}} \right) \to 3{\rm{AgN}}{{\rm{O}}_{\rm{3}}} + {\rm{N}}{{\rm{O}}_{\rm{2}}} + 2{{\rm{H}}_{\rm{2}}}{\rm{O}}$


Next metal is lead (Pb). Lead reacts with concentrated nitric acid to form lead nitrate and hydrogen.

${\rm{Pb}} + 4{\rm{HN}}{{\rm{O}}_{\rm{3}}} \to {\rm{Pb}}{\left( {{\rm{N}}{{\rm{O}}_{\rm{3}}}} \right)_2} + 2{\rm{N}}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}$


So, we can say that iron and platinum do not undergo reaction with concentrated nitric acid.

So, the correct answer is Option A .

Note:
Nitric acid is mainly used in the production of ammonium nitrate which is used in preparation of fertilizer and other nitrates which are used in explosives. Some other major uses of nitric acid are etching of metals, pickling of stainless steel etc.