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    The p-Block Elements
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    Illustrate how copper metal can give different products with HNO3.
    Concentrated nitric acid is strong oxidizing agent.
    The product of oxidation depend on the concentration of acid, temperture and also the material undergoing oxidation.
    Two condition aries :
    On heating with dilute nitric oxide NO evolved or on reacting with concentrated nitric acid NO2 is evolved.

    reaction with dilute nitric acid 3Cu +8HNO3(dil) →3Cu(NO3)2 +4H2O +2NOReaction with concentrated nitric acidCu +2HNO3(conc.)→Cu(NO3)2 +2H2O +2NO2
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    Why does NH3 form hydrogen bond but PH3 does not? 
    Formation of hydrogen bonding depend on the size of  molecule. smaller the size greater the hydrogen bonding. Nitrogen has smaller size than phosphrous thus having a more abilty to form hydrogen bond.
    N—H bond is reasonably polar and this leads to hydrogen bonding. As the bond polarity of the P—H bond is almost negligible, PH    3is not involved in hydrogen bonding.
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    Why does the reactivity of nitrogen differ from phosphorus?
    Nitrogen molecule is a diatomic and the two nitrogen atoms are linked by triple bond (N≡ N). Forming a pπ -pπ bonding and thus the bond dissociation energy is very high (946 kj mol–1), it is not possible to cleave the triple bond so easily. Therefore, the reactivity of nitrogen differ from phosphorus.
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    How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions involved.  
    Nitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.

    NH4Cl(aq) + NaNO2(aq)  →  N2(g) + 2H2O(l) + NaCl(aq)
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    How is ammonia manufactured industrially? 

    Ammonia is manufactured industrially by Haber's process.
    N2(g) + 3H2(g) ⇌ 2NH3(g)  ∆f H° = -46.1 kJ mol-1

    A mixture of dry nitrogen and hydrogen gases in the ratio of 1:3 by volume is compressed to about 200 to 300 atm and passed over iron catalyst at a temperature of about 723 k to 773 k. The iron catalyst is mixed with aluminium oxide (Al    2O3) and potassium oxide (K2O) which act as promotors.
    Ammonia being formed is continuously removed by liquefying it. 
    The optimum conditions for the production of ammonia are a pressure of about 200 atm, a temperature of ~700 k and use of a catalyst such as iron oxide with small amounts of K2O and Al2,O3 to increase the rate of attainment of equilibrium.
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