Question

Referring to the following reactions the missing products A,B,C, and D respectively are

• A. $N_{2}, \, N_{2}, \, NO, \, NO_{2}$
• B. $N_{2}, \, NH_{3}, \, N_{2}, \, NO$
• C. $N_{2}, \, N_{2}, \, NO_{2}, \, NO_{2}$
• D. $N_{2}, \, NH_{3}, \, NO_{2}, \, N_{2}O_{4}$

Answer 1

Answer: (A)

(i) In the laboratory, dinitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.
$ NH _{4} Cl ( aq )+ NaNO _{2}( aq ) \rightarrow N _{2}( g )+2 H _{2} O ( l )+ NaCl ( aq ) $
Small amounts of $NO$ and $HNO _{3}$ are also formed as impurities, which can be removed by passing the gas through aqueous sulphuric acid containing potassium dichromate.
(ii) Dinitrogen can also be prepared by heating ammonium dichromate
$ \left( NH _{4}\right)_{2} Cr _{2} O _{7}( s ) \stackrel{\Delta}{\longrightarrow} N _{2}( g )+4 H _{2} O ( l )+ Cr _{2} O _{3}( s ) $
(iii) Copper metal reacts with dilute $HNO _{3}$ to form nitrogen (II) oxide (NO)
$ 3 Cu ( s )+8 HNO _{3}(\text { dilute }) \rightarrow 3 Cu \left( NO _{3}\right)_{2}( aq )+2 NO ( g )+4 H _{2} O ( l ) $
(iv) Copper metal reacts with conc. $HNO _{3}$ to form nitrogen (IV) oxide or nitrogen dioxide $\left( NO _{2}\right)$.
$ \left. Cu ( s )+4 HNO _{3} \text { (conc. }\right) \rightarrow Cu \left( NO _{3}\right)_{2}( aq )+2 NO _{2}( g )+2 H _{2} O ( l ) $$ NH _{4} Cl ( aq )+ NaNO _{2}( aq ) \rightarrow N _{2}( g )+2 H _{2} O ( l )+ NaCl ( aq ) $
Small amounts of $NO$ and $HNO _{3}$ are also formed as impurities, which can be removed by passing the gas through aqueous sulphuric acid containing potassium dichromate.
(ii) Dinitrogen can also be prepared by heating ammonium dichromate
$ \left( NH _{4}\right)_{2} Cr _{2} O _{7}( s ) \stackrel{\Delta}{\longrightarrow} N _{2}( g )+4 H _{2} O ( l )+ Cr _{2} O _{3}( s ) $
(iii) Copper metal reacts with dilute $HNO _{3}$ to form nitrogen (II) oxide (NO)
$ 3 Cu ( s )+8 HNO _{3}(\text { dilute }) \rightarrow 3 Cu \left( NO _{3}\right)_{2}( aq )+2 NO ( g )+4 H _{2} O ( l ) $
(iv) Copper metal reacts with conc. $HNO _{3}$ to form nitrogen (IV) oxide or nitrogen dioxide $\left( NO _{2}\right)$.
$ \left. Cu ( s )+4 HNO _{3} \text { (conc. }\right) \rightarrow Cu \left( NO _{3}\right)_{2}( aq )+2 NO _{2}( g )+2 H _{2} O ( l ) $