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..