10.2 Nitric Oxide $NO$ (Neutral)

  p Block Elements

Preparation:

(a) By the reaction of dilute nitric acid on copper (Lab, method), the nitric oxide liberatd is collected over water.\[Ag/Hg/Pb/3Cu + 8HN{O_3} \to 3Cu{(N{O_3})_2} + 2NO + 4{H_2}O\]The liberated gas may contain $NO_2$ and $N_2O$.These are saperated by passing the mixture through ferous sulphate solution, $NO$ forms a dark nitroso-ferrous sulphate. When this solution is heated, pure nitric oxide is liberated.\[\begin{gathered} FeS{O_4} + NO \to FeS{O_4}.NO\xrightarrow{{Heat}}FeS{O_4} + NO \hspace{1em} \\ \quad \quad \quad (\operatorname{Impure\;gas) } \;\;Dark\;Brown)\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;(Pure\;Gas) \hspace{1em} \\ \end{gathered} \]

(b) A pure sample of nitric oxide is obtained when a mixture of $KNO_3,FeSO_4$ and dilute $H_2SO_4$ is heated. This is also a laboratory method.$$2KN{O_3} + 6FeS{O_4} + 4{H_2}S{O_4} \to {K_2}S{O_4} + 3F{e_2}{(S{O_4})_3} + 2NO + 4{H_2}O$$

(c) Nitric oxide is the first product obtained from the following two processes during the manufacture of nitric acid.

(i) Electric process:

By passing an electric arc, nitrogen, and oxygen of the air combine together to form nitric acid.\[{N_2} + {O_2}\overset {Electric\;arc} \leftrightarrows 2NO\]

(ii) Oswald's process:

By restricted oxidation of ammonia with air in presense of platinum gauze at 750, nitric oxide is formed.

\[4N{H_3} + 5{O_2}\xrightarrow[{750^\circ C\;6 - {\kern 1pt} atm}]{{Pt.\;gauze}}4NO + 6{H_2}O\]

Properties:

(a) It is sparingly soluble in water.

(b) It is paramagnetic indicating the presence of the unpaired electron in the molecule.

(c) It is neutral to litmus.

(d) It at once reacts with oxygen to give brown fumes of nitrogen dioxide.\[2NO + {O_2} \to 2N{O_2}\]

(e) It is stable oxide, It decomposes into nitrogen and oxygen when heated at $800^\circ C$

\[2NO\xrightarrow{{800^\circ C}}{N_2} + {O_2}\]

(f) It is combustible and supports combustion of boiling sulphur and burning phosphorous.$$S + 2NO \to S{O_2} + {N_2}$$

(g) It dissolves in cold ferrous sulphate solution by forming a hydrated nitrosyl complex.

$$\begin{equation} \begin{aligned} \left[ {Fe{{({H_2}O)}_6}} \right]S{O_4} + 4NO \to \left[ {Fe{{({H_2}O)}_5}NO} \right]S{O_4} + {H_2}O \\ Ferrous\;sulphate\;\;\;\;\;\;\;\;\;\;\;\;\;\;Hydrated\;nitrosyl \\ \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;complex\;(Brown\;colour) \\ \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\; \downarrow \Delta \\ \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;FeS{O_4} + 4NO + 5{H_2}O \\\end{aligned} \end{equation} $$

(Stannous chloride reduces nitric oxide to hydroxylamine)

\[\frac{\begin{gathered} \left[ {SnC{l_2} + 2HCl \to SnC{l_4} + 2H} \right] \times 3 \hspace{1em} \\ 2NO + 6H \to 2N{H_2}OH \hspace{1em} \\ \end{gathered} }{{3SnC{l_2} + 6HCl + 2NO \to 3SnC{l_4}2N{H_2}OH}}\]

(h) Nitric oxide directly combines with halogen (fluorine, chlorine, bromine) to form corresponding nitrosyl halides.$$\begin{equation} \begin{aligned} 2NO\;\;\;\;\; + \;\;\;\;{X_2}\;\;\;\;\;\;\;\;\;\;\;\; \to \;\;\;\;\;\;\;\;2NOX \\ \;\;\;\;\;\;\;\;\;({F_2},C{l_2}\;or\;B{r_2})\;\;\;\;\;\;\;\;\;\;\;\;\;\;Nitrosyl\;halide \\\end{aligned} \end{equation} $$

Uses:

(i) In the manufacture of nitric acid.

(ii) As a catalyst in lead chamber process for the manufacture of sulphuric acid.

(iii) In the detection of oxygen to distinguish it from nitrous oxide.