Group 15 elements(nitrogen group) NCERT QUESTIONS (REASONING)

  NCERT QUESTIONS (REASONING) 

 Q.1 Why BiH3 is the strongest reducing agent amongst all the hydrides of Group 15 elements ?  

Ans. In hydrides of nitrogen family on moving down the group M–H bond length increases so bond strength decreases hence tendency to release hydrogen increases and reducing nature increases. Increasing order of reducing nature is NH3 < PH3 < AsH3 < SbH3 < BiH3 

 

Q.2 Write the reaction of thermal decomposition of sodium azide.  

Ans. Thermal decomposition of sodium azide gives dinitrogen gas. 2NaN3 --------->2Na + 3N2  

Q.3 Why N2 is less reactive at room temperature?  

Ans. N2 is less reactive at room temperature because of the high bond enthalpy of NºN bond. 

Q.4 Why does R3P = O exist but R3N = O does not (R = alkyl group)?  

Ans. Due to presence of vacant d orbital phosphorous can form five covalent bond, while nitrogen restricts its covalency to four due to absence of vacant d orbitals.  

Q.5 Why does nitrogen show catenation properties less than phosphorus?  

Ans. N–N bond is weaker than the single P–P bond due to high interelectronic respulsion of non-bonding electrons as a result the catenation tendency is weaker in nitrogen.  

Q.6 Mention the conditions required to maximise the yield of ammonia.  

Ans. In accordance with Le Chatelier’s principle, high pressure would favour the formation of ammonia. The optimum conditions for the production of ammonia are a pressure of 200 × 105 Pa (about 200 atm), a temperature of ~ 700 K and the use of a catalyst such as iron oxide with small amounts of K2O and Al2O3 to increase the rate of attainment of equilibrium.  

Q.7 How does ammonia react with a solution of Cu2+?  

Ans. The presence of a lone pair of electrons on the nitrogen atom of the ammonia molecule makes it a Lewis base. It donates the electron pair and forms linkage with metal ions and the formation of such complex compounds finds applications in detection of Cu2+ .  

 Cu2+ (aq) +  4NH3 (aq)        ------------> [Cu (NH3)4]2+ (aq) 

(blue)                                                        (deep blue) 

Q.8 Illustrate how copper metal can give different products on reaction with HNO3.  

Ans. 3Cu + 8 HNO3 (dilute) ----------> 3Cu (NO3) 2 + 2NO + 4H2O 

            Cu + 4HNO3 (conc.)  --------->    Cu (NO3) 2 + 2NO2 + 2H2O  

Q.9 Why is nitrogen di-oxide paramagnetic in gaseous state but the solid obtained on cooling it is diamagnetic.  

Ans. NO2 contains odd number of electrons in its valence shell. On cooling it forms dimer and converted to stable N2O4 which is a colourless solid and diamagnetic in nature.  

Q.10 Why NH3 gas cannot be dried by passing over P2O5, CaCl2 and H2SO4?  

Ans. CaCl2 + 8NH3 --------> CaCl2 .8NH3  

         P2O5 + 6NH3 + 3H2O ------> 2(NH4) 3 PO4  

         H2SO4 +2NH3--------> (NH4) 2 SO4 

          So it is dried by passing over quick lime  

           (CaO). CaO + H2O -------> Ca (OH)2