Inorganic chemistry

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Here are a few common methods of preparation of some important compounds of $P ~block~elements$ P block

Group 15

1)Dinitrogen ($N_2$) :

Laboratory method : $\ce{ NH_4Cl_(aq) + NaNO_2_(aq) \rightarrow N_2 + 2H_2O_(l) + NaCl_(aq)}$

Very pure $N_2$ can be obtained by thermal decomposition of Sodium or Barium azide

$\ce{ Ba(N_3)_2 \rightarrow Ba + 3N_2}$

2)Ammonia ($NH_3$):

commercial method:$\ce{N_2 + 3H_2 \rightarrow 2NH_3....(Haber's process)}$

optimum conditions for commercial production- $200 ~atm ~pressure$

$700 K(temperature)$,

catalyst $\ce{ FeO}~ \text{with}~~ \ce{ K_2O } ~ and ~\ce{ Al_2O_3}~ promoters$

3)Nitric acid ($HNO_3$ )

$\ce{ NH_3_ (g) + 5 O_2 \rightarrow 4 NO + 6 H_2O }$

$\ce{2 NO + O_2 \rightleftharpoons 2 NO_2 (g)}$

$\ce{3 NO_2 (g) +H_2O(l) \rightarrow 2 HNO_3 (aq) +NO(g)}$

$\ce{HNO_3 + NO}$ mixture is called fuming nitric acid

optimum condition: $500 K~,9$bar pressure,$Pt/Rh$ gauge catalyst

4) $\text{Phosphorous Trichloride}- \ce{PCl_3}$

Preparation :

$\ce{P_4 + 8 SOCl_2 \rightarrow 4 PCl_3 +4 SO_2 + 2S_2Cl_2}$

5) $\text{Phosphorous Pentachloride}-\ce{ PCl_5}$

Preparation :

$\ce{P_4 +10 SO_2Cl_2 \rightarrow 4 PCl_5 + 10 SO_2}$

6)$Phosphine - \ce{PH_3}$

Preparation :

Phosphine can be prepared by reacting white phosphorus with hot $\ce{NaOH}$ in an inert atmosphere of $\ce{CO_2}$

$\ce{P_4 + 3NaOH + 3H_2O \rightarrow PH_3 +NaH_2PO_2}$

Group 16

1)Dioxygen ($O_2$)

By heating oxygen containing salts such as chlorates ,nitrates and permanganates in the presence of catalysts such as MnO2.

$\ce{2KClO_3 \rightarrow 2KCl + 3O_2}$

It is also obtained by the electrolysis of water .

2)Sulphuric Acid- $\ce{H_2SO_4}$

By contact process :

$Steps:$

a)burning of sulphur or sulphide ores to generate $SO_2$ which is converted to $SO_3$

$\ce{ 2SO_2 + O_2 \rightarrow 2SO_3 }$ catalyst: $V_2O_5$.

b)absorption of $SO_3$ by$H_2SO_4$ to give Oleum.

$\ce{SO_3 + H_2SO_4 \rightarrow H_2S_2O_7}$

The sulphuric acid so obtained is 96-98% pure.

Group 17

1)Dichlorine ($Cl_2$)

By Deacon's process......catalyst: $CuCl_2$

$\ce{4HCl + O_2 \rightarrow 2Cl_2 + 2H_2O }$

2)Hydrochloric acid(HCl)

$\ce{NaCl + H_2SO_4 \rightarrow NaHSO_4 + HCl } .... T:420 K$

$\ce{NaHSO_4 + NaCl \rightarrow Na_2SO_4 + HCl }......T: 823 K$

Acid so obtained is dried using Conc sulphuric Acid..