The p Block Elements

GROUP 15 ELEMENTS
Elements of group 15 are called members of N-family, consists of nitrogen (N), phosphorous (P), arsenic (As), antimony (Sb) and bismuth (Bi).  Nitrogen and phosphorus are non-metals; arsenic and antimony are metalloids; bismuth is metallic.  Beside nitrogen, the other important element of group 15 is phosphorous.  These elements are also known as pnicogens and their compounds as pnicomides.

Electronic configuration: The general electronic configuration of pnicogens is ns²np³, where n = 2 to 6.

Element	At. No.	Electronic configuration
N	7	[He] 2s22p3
P	15	[Ne] 3s2 3p3
As	33	[Ar] 3d10, 4s2 4p3
Sb	51	[Kr] 4d10, 5s2 5p3
Bi	83	[Xe] 4f14, 5d10, 6s26p3

Occurrence:  Nitrogen occurs in free as well as in combined state.  In atmospheric air percentage of nitrogen is 75% by mass and 78% by volume.  In combined state it mostly found as nitrates (i.e., chile salt petre-NaNO₃, saltpeter – KNO₃), proteins and amino acids while, phosphorus is an active element.  It does not occur free in nature.  It is the 11^th most abundant element in earth’s crust.  It is essential for life of both plants and animals.  It is widely distributed in nature in the combined state.  The main minerals of phosphorus are
(i)  Phosphite            –     Ca₃ (PO₄)₂
(ii)  Flourapatite       –     3Ca₃(PO₄)₂.CaF₂
(iii) Chlorapatite       –     3 Ca₃ (PO₄)₂.CaCl₂
(iv) Hydroxyapatite  –     Ca₅ (PO₄)₃(OH)
An average person has 3.5 kg of calcium phosphate in his body.  Phosphorous is also present in DNA, RNA, ATP, ADP etc.
As, Sb, Bi occur as sulphides or oxides.

Minerals of arsenic:
(i) Realgar             –     As₄S₄ (red-orange)
(ii) Orpiment        –     As₂S₃ (yellow)
Minerals of antimony:
(i) Stibinite            –     Sb₂S₃
(ii) Flue dust         –     Sb₂O₃
Minerals bismuth:
(i) Bismuth glance   –     Bi₂S₃
(ii) Bismuth ochre   –     Bi₂O₃
(iii) Bismuthite         –     BiO₂CO₃

Atomic and Physical Properties:
1. Atomicity and Physical state: At room temperature nitrogen is a diatomic gas after hydrogen whereas other member of this group are solids.  The physical property of these elements gradually changes from gaseous state to solid state.  Hence nitrogen is a covalent molecule, which is formed by

i)  p_x – p_x overlap

ii)  p_y – p_y overlap

iii)  p_z – p_z overlap

Thus, in nitrogen molecule a triple bond is present between the two nitrogen atom.  Therefore, one sigma bond and two pie bonds are formed by p_x – p_x, py – py and p_z – p_z overlapping respectively.  It is inactive in normal chemical reactions due to its higher dissociation energy (i.e., 945.4 kJ).  On the other hand, phosphorus is waxy solid at room temperature. It is a tetratomic molecule (P₄).  It has a regular tetrahedron structure having one P atom at each vertex of the tetrahedron.  (∠PPP = 60⁰).  Whereas all the other elements of this group (VA) are normally solids.

Tetrahedral structure of P4 molecule (As, Sb also)

2. Atomic radius: Atomic radii as well as covalent radii increase with increase in atomic number from Nitrogen to Bismuth.

Density increases down the group (d = m/v).  Atomic No. & Atomic wt = Increases down the group (N → Bi).

3. Ionization enthalpy (kJ/mol): Ionization energy of nitrogen is very high due to small atomic radius.  The ionization energy decreases down the group.
Order of

IE₁ :     N > P > As > Sb > Bi
IE₂ :     N > P > As > Bi < Sb
IE₃ :     N > P > As > Bi < Sb

4. Electronegativity: Electronegativity of nitrogen is 3.0 on Paulling scale.  The electronegativity decreases down the group (N → Bi).

Element	N	P	As	Sb	Bi
EN	3.0	2.1	2.0	1.9	1.9

5. Metallic character:

$\underset{\text{ non}-\text{metals}}{\underbrace{\mathrm{N} \mathrm{P}}} \underset{\text{ Metalloids }}{\underbrace{\text{As }\text{Sb}}} \underset{\text{metal }}{ \underbrace{ \mathrm{Bi} }}$

6. Melting points (K): Melting point of the elements of group 15 first increases then decreases down the group.

Element	N	P	As	Sb	Bi
MP(K)	63	317	1089	904	544

7. Boiling points:

Element	N	P	As	Sb	Bi
BP(K)	77	554	888	1860	1837

8. Catenation: All these elements show the property of catenation but to a much smaller extent than carbon, due to less M – M bond dissociation energy i.e. the catenation capacity depends on M-M bond energy.  Thus, catenation capacity gradually decreases down the group.

Bond	C – C	N – N	P – P	As – As
BE (kJ/mol)	353.3	163.8	201.6	147.4

Thus, nitrogen forms longer chain as compared to phosphorus.  e.g., hydrazine (NH₂NH₂) has two ‘N’ – atoms bonded together, hydrozoic acid (NH₃H) has three N – atoms bonded together longer while diphosphine (P₂H₄) has two ‘P’ – atoms bonded together.

9. Allotropy : (Greek : allos = another, trops = shape): The property of an element to exist in two or more physical forms, having more or less similar chemical properties but different physical properties, is called as allotropy.  The different form are called allotropes or allotropic modifications.
All elements of group 15 show allotropy (except Bi).
Nitrogen            :  α-Nitrogen,  β-Nitrogen
Phosphorous   :  White P Red P, Scarlet P, violet P, α – black P, β – black P.
Arsenic               :  Grey, Yellow, Black. 
Antimony          :  Yellow or silvery grey, explosive black.

10. Oxidation states: The elements of group 15 have five electrons (ns²np³) in their outermost shell (n)
These elements exhibit a maximum oxidation state of + 5 towards oxygen by using all the five valence electrons.  Common oxidation states of these elements are + 3, + 5.  Stability of + 3 oxidation state increases down the group because inert pair effect increases down the group while stability of + 5 oxidation state, decreases (down the group).  Nitrogen exhibits a wide range of oxidation states.

Oxidation state	Examples
– 3	NH3, NH4+, NH2–
– 2	NH2NH2
– 1	NH2OH, NH2F
0	N2
+ 2	NO
+ 3	HNO2, NO2–, NF3
+ 4	NO2, N2O4
+ 5	N2O5, HNO3, NO3

N and P generally exhibit -3 O.S. due to high electronegativity & small size.  N forms nitride ion N^3– with highly electropositive elements.  P also forms phosphide ion P^3– to some extent.

Illustration 1: Why does nitrogen in ammonia exhibit negative oxidation state?
Solution: The high ionization energy, high electronegativity and small size of N-atom is responsible for ‘-3’ state of ‘N’.
Illustration 2: What is the oxidation state of phosphorous in the following
(i)  H₃PO₃    (ii)  PCl₃    (iii)  Ca₃P₂    (iv)  Na₃PO₄    (v)  POF₃
Solution:  i)  + 3                     ii)  + 3                       iii)  – 3              iv)  + 5               v)  + 5

Chemical properties:
1. Formation of Hydrides: All the elements of group 15 form gaseous trihydrides of the general formula MH₃, which are covalent and trigonal pyramidal in shapes.
Some properties, such as (i)  ease of formation (ii)  basic character    (iii)  solubility     (iv)  stability (v) dipole moment (vi)  bond angle   (vii)  strength of M – H bond  (viii)  decomposition temperature, follow the order given below.

Some properties like (i)  reducing character (ii)  covalent character   (iii)  poisonous character  (iv)  rate of combustion, follow the order given below.
${\mathrm{NH}}_3<{\mathrm{PH}}_3<{\mathrm{AsH}}_3<{\mathrm{SbH}}_3<{\mathrm{BiH}}_3$
Order of MP :  ${\mathrm{NH}}_3>{\mathrm{SbH}}_3>{\mathrm{AsH}}_3>{\mathrm{PH}}_3-$           
Order of BP :   ${\mathrm{BiH}}_3>{\mathrm{SbH}}_3>{\mathrm{NH}}_3>{\mathrm{AsH}}_3>{\mathrm{PH}}_3$

Methods of preparation of some hydrides:
$\begin{array}{l}{\mathrm{Mg}}_3{\mathrm{N}}_2+6{\mathrm{H}}_2\mathrm{O}⟶3\mathrm{Mg}(\mathrm{OH}{)}_2\downarrow +2{\mathrm{NH}}_3\uparrow \\ \\ {\mathrm{Ca}}_3{\mathrm{N}}_2+6{\mathrm{H}}_2\mathrm{O}⟶3\mathrm{Ca}(\mathrm{OH}{)}_2+2{\mathrm{NH}}_3\\ \\ {\mathrm{Ca}}_3{\mathrm{P}}_2+6{\mathrm{H}}_2\mathrm{O}⟶\mathrm{Ca}(\mathrm{OH}{)}_2+2{\mathrm{PH}}_3\uparrow \\ \\ {\mathrm{Ca}}_3{\mathrm{P}}_2+6\mathrm{HCl}⟶3{\mathrm{CaCl}}_2+2{\mathrm{PH}}_3\uparrow \end{array}$

$\begin{array}{l}\underset{\mathrm{white}}{{\mathrm{P}}_4}+3\mathrm{KOH}+3{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{PH}}_3+\underset{\mathrm{Sod}. \mathrm{hypophosphite}}{3{\mathrm{KH}}_2{\mathrm{PO}}_2}\\ \\ \mathrm{BN}+3{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{H}}_3{\mathrm{BO}}_3+{\mathrm{NH}}_3\\ \\ \mathrm{AIN}+3{\mathrm{H}}_2\mathrm{O}⟶\mathrm{Al}(\mathrm{OH}{)}_3+{\mathrm{NH}}_3\\ \\ {\mathrm{PH}}_4\mathrm{I}+\mathrm{NaOH}⟶\mathrm{Nal}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{NH}}_3\end{array}$
Structure of the hydrides:  All these hydrides are covalent and have trigonal pyramidal structure and the hybridization is sp³.

Structure of NH3 & PH3

In general, the force of repulsion between bonded pairs of electrons decreases as we move from NH₃ to BiH₃ and therefore, the bond angle also decreases from NH₃ to BiH₃.

Illustration 3: Ammonia is a good complexing agent.  Explain.
Solution: Ammonia is good complexing agent because of the presence of lone pair of electrons on nitrogen.  This lone pair can easily be donated to electron deficient compounds forming complexes.
Illustration 4: Among the hydrides of group 15, predict the hydride having
i) most basic character
ii) highest thermal stability
iii) lowest boiling point
iv) strongest reducing agent                    
Solution: i)  NH₃               ii)  NH₃                                                    iii)  PH₃                      iv)  BiH₃

2. Formation of halides: Elements of group 15 form two series of halides i.e., Trihalides (MX₃) and penta halides (MX₅).
Trihalides (MX₃):  These are formed by all elements of group 15.
These are predominantly covalent in nature (except BiF₃ – ionic). Trihalides are formed by the direct reaction of elements with halogens.
Preparation:  i)  ${\mathrm{P}}_4+6{\mathrm{Cl}}_2\underset{\mathrm{direct}}{\overset{{}^{\mathrm{\Delta }}}{\to }}4{\mathrm{PCl}}_3 \left(\text{except}\mathrm{N}\right)$

ii) The trihalides are also formed when a suitable compound is treated with the halogen.

$\begin{array}{l}{\mathrm{NH}}_3+3{\mathrm{Cl}}_2⟶{\mathrm{NCl}}_3+3\mathrm{HCl}\\ \\ 2{\mathrm{PCl}}_3+3{\mathrm{F}}_2⟶2{\mathrm{PF}}_3+3{\mathrm{Cl}}_2\end{array}$

Structure: The trihalides have a pyramidal structure like hydrides and the hybridization is sp³.

Characteristics of trihalides:  All the trihalides are stable except NCl₃, NBr₃, NI₃ due to low polarity of N-x bond and a large difference in the size of nitrogen and halogen atoms.  NF₃ is a colourless, odourless gas and most stable trihalide.  It has low reactivity.
NCl₃ is a yellow oily liquid.  It reacts with water to form ammonia and hypochlorous acid where as NI₃ is shock sensitive and decomposes explosively when touched. 
These act as a lewis base due to presence of one lone pair on the central atom.  In case of trihalides of nitrogen basic character decreases from NI₃ to NF₃.
${\mathrm{NI}}_3>{\mathrm{NBr}}_3>{\mathrm{NCl}}_3>{\mathrm{NF}}_3$
The trihalides of phosphorous antimony especially fluorides and chlorides act as Lewis acid also by using the vacant d-orbitals.
e.g.,  ${\mathrm{PF}}_3+{\mathrm{F}}_2⟶{\mathrm{PF}}_5; {\mathrm{SbF}}_3+2{\mathrm{F}}^{-}⟶{\left[{\mathrm{SbF}}_5\right]}^{2-}$
All the trihalides are hydrolysed with water except NF₃ and PF₃.
$\begin{array}{l}{\mathrm{NCl}}_3+3{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{NH}}_3+3\mathrm{HOCl} \text{(hypochlorous acid)}\\ \\ {\mathrm{PCl}}_3+3{\mathrm{H}}_2\mathrm{O}⟶\underset{\text{phosphorousacid}}{{\mathrm{H}}_3{\mathrm{PO}}_3+}3\mathrm{HCl}\\ \\ 2{\mathrm{AsCl}}_3+2{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{As}}_2{\mathrm{O}}_3+6\mathrm{HCl}\end{array}$
SbCl₃ and BiCl₃ are only partially hydrolysed to form oxychlorides.

$\begin{array}{l}{\mathrm{SbCl}}_3+{\mathrm{H}}_2\mathrm{O}⟶\underset{\text{Antimonyoxychloride}}{\mathrm{SbOCl}+2\mathrm{HCl}}\\ \\ {\mathrm{BiCl}}_3+{\mathrm{H}}_2\mathrm{O}⟶{\underset{\text{Bismuthoxychloride}}{\mathrm{BiOCl}}}_{}+2\mathrm{HCl}\end{array}$
Order of ease of hydrolyses:  BiCl₃ > SbCl₃ > AsCl₃ > PCl₃ > NCl₃.

Pentahalides (MX₅):
All the elements of group 15 form pentahalides except nitrogen.  Nitrogen does not form pentahalides due to the absence of vacant d-orbitals in its outer most shell.  Bismuth also, does not form pentahalides because of inert pair effect.
Preparation:  The pentahalides are formed by the reaction of these elements with an excess of halogens.
$\begin{array}{rl}& {\mathrm{P}}_4+\underset{excess}{10{\mathrm{Cl}}_2}\stackrel{∆}{\to }\underset{phosphorous pentachloride}{{4\mathrm{PCl}}_5}\end{array}$
Structure:  All the pentahalides have a trigonal bipyramidal shape with sp³d hybridization.

Trigonal bipyramidal shape of pentahalides.

Characteristics of pentahalides:

PF₅ exists as molecule in both gaseous and solid states.  PCl₅ exists as molecule in the gas phase but exists as [PCl₄]⁺ [PCl₆]^– in the crystalline state.  PBr₅ and PI₅ are also exist in the ionic form as ${\left[{\mathrm{PBr}}_4\right]}^{+}{\left[{\mathrm{PBr}}_6\right]}^{-} \text{and }{\left[{\mathrm{PI}}_4\right]}^{+}{\mathrm{I}}^{–}$ respectively in solid state.

PCl₅ is used as a starting materials for a variety of organophosphorus compounds and fumes in air and acts as an effective chlorinating agent. These pentahalides completely hydrolysed and form corresponding acids.

$\begin{array}{rl}& ({\mathrm{PCl}}_5+{\mathrm{H}}_2\mathrm{O}\underset{\text{hydrolysis}}{\overset{\text{partal}}{\to }}{\mathrm{POCl}}_3+2\mathrm{HCl})\\ & \\ & {\mathrm{POCl}}_3+\underset{}{\underset{\text{ecoses}}{3{\mathrm{H}}_2\mathrm{O} }\underset{\text{hydrolysis}}{\overset{\mathrm{complete}}{\to }} }\underset{\mathrm{hydrhophasphoric}acid}{{{\mathrm{H}}_3\mathrm{PO}}_4}+3\mathrm{HCl}\end{array}$
These pentahalides are thermally less stable than trihalides, in gaseous and liquid states.  i.e., In gaseous and liquid states these pentahalides are not very stable, hence they decompose into trihalides. ${\mathrm{PCl}}_5 \to {\mathrm{PCl}}_3+{\mathrm{Cl}}_2$

Illustration 5: NF₃ does not have donor properties like animonia.  Explain.
Solution: NF₃ has a pyramidal shape with one lone pair on N-atom.

In NF₃, lone pair on N – is in opposite direction to the N – F bond moments and therefore, it has very low dipole moment (μ = 0.234D).  Thus, it does not show donor properties but ammonia has high dipolemoment because its lone pair is in the same direction as the N – H bond moments.  Thus, it has donor properties.

Illustration 6: Compare the acidic nature of PCl₃ and PCl₅.
Solution: Both PCl₃ and PCl₅ are acidic.  PCl₅ is more acidic than PCl₃ as the former gives phosphorous acid and later gives phosphoric acid on hydrolysis.

Oxides formation: All the elements of this group form two series of oxides i.e., trioxides (M₂O₃) and pentaoxides (M₂O₅). 
Nitrogen forms several oxides in which the oxidation state varies from + 1 to + 5.

Oxides of N:	$\underset{\text{neutral}}{\underbrace{{\stackrel{+1}{{\mathrm{N}}_2\mathrm{O}}}_{ }\stackrel{+2}{\mathrm{NO}}} }$	${\mathrm{N}}_2^{+3}{\mathrm{O}}_3$	${\mathrm{N}}_2^{+4}{\mathrm{O}}_4$	${\mathrm{N}}_{{}_2}^{+5}{\mathrm{O}}_5$
Oxides of P:		P2O3 (or P4O6	P4O8 or (P2O4)	P2O5 (or P4O10) more acidic
Oxides of As:		As2O3	As2O4	As2O5
Oxides of Sb:		Sb2O3	Sb2O4	Sb2O5
Oxides of Bi:		Bi2O3	Bi2O4	Bi2O5

Trioxides and pentaoxide are also represented as M₄O₆ and M₄O₁₀ respectively.
Acidic character of oxides ∝ EN ∝ O.S of element in same oxides.
In the oxides of particular elements, the acidic nature increases as the percentage of oxygen increases or as the oxidation state increases.
For example:  N₂O₅ is most acidic while N₂O₃ is less acidic.  Similarly, P₂O₅ is more acidic than P₂O₄ and P₂O₃.
Thermal stability of oxides of higher oxidation states decreases with increasing atomic number (down the group).  i.e., Thermal stability, in each series decreases from N to Bi.  e.g., N₂O₃ is most stable oxide and N₂O₅ is less stable. 
However P₂O₅ is stable but As₂O₅, Sb₂O₅, Bi₂O₅ (least) are less stable.   Pentaoxides act as oxidizing agent (except P₂O₅).  Among these oxidise N₂O₅ is the strongest oxidizing agent.  The oxides of N & P are chemically similar while their structures are – different.

Preparation, properties and structures of oxides of Nitrogen and phosphorus:
1) Nitrousoxide (N₂O) : It is also known as dinitrogen oxide or nitrogen monoxide or laughing gas.

Prep: (i) ${\mathrm{NH}}_4{\mathrm{NO}}_3\stackrel{\mathrm{△}}{⟶}{\mathrm{N}}_2\mathrm{O}+2{\mathrm{H}}_2\mathrm{O} \left(\text{Bertholet}\right)$

(ii) $2{\mathrm{NaNO}}_3+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4⟶2{\mathrm{N}}_2\mathrm{O}+4{\mathrm{H}}_2\mathrm{O}+{\mathrm{Na}}_2{\mathrm{SO}}_4$

Prop. It is a stable, relatively unreactive, colourless natural gas, with pleasing odour and sweet taste. It supports combustion.
$2{\mathrm{N}}_2\mathrm{O}\left(\mathrm{g}\right)\stackrel{∆}{⟶}2{\mathrm{N}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$

Structure :  N₂O is a linear molecule.

Uses :  Mixed with oxygen, it is used as anaesthetic i.e., usually N₂O is administered to the patient put him to sleep. 
2)  Nitric oxide or nitrogen oxide (NO):

Prep : i) $\underset{}{\underset{\left(\mathrm{g}\right)}{{\mathrm{N}}_2}+\underset{\left(\mathrm{g}\right)}{{\mathrm{O}}_2\stackrel{∆}{\to }}}2\mathrm{NO}\left(\mathrm{g}\right) \text{(commercial method)}$
ii)  $4{\mathrm{NH}}_3+5{\mathrm{O}}_2\underset{\begin{array}{c}\text{Pt catalyst}\\ {750}^{\circ }\mathrm{C},6\mathrm{atm}\end{array}}{\overset{∆}{\to }}\mathrm{NO}+6{\mathrm{H}}_2\mathrm{O} (\text{Ostwald method)}$
Prop: Colourless, paramagnetic toxic gas. It is combustible and supports combustion.

i)  $2\mathrm{NO}+{\mathrm{O}}_2⟶2{\mathrm{NO}}_2 \left(\text{brown}\right)$

ii) ${\mathrm{FeSO}}_4+\mathrm{NO} \to \underset{\mathrm{dark} \mathrm{brown}}{{\mathrm{FeSO}}_4\cdot \mathrm{NO}}\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{FeSO}}_4+\underset{\mathrm{Pure} \mathrm{gas}}{\mathrm{NO}}$

iii)  $\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\mathrm{SO}}_4+\mathrm{NO}⟶\underset{\mathrm{Hydrated} \mathrm{Nitrosyl} \mathrm{complex}}{\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{NO}\right]{\mathrm{SO}}_4}\stackrel{∆}{\to }{\mathrm{FeSO}}_4+\mathrm{NO}+5{\mathrm{H}}_2\mathrm{O}$

Structure:  

Uses:

i)  As reducing as well as oxidizing agent.
ii) For manufacturing of HNO₃ and H₂SO₄ (as catalyst in lead chamber process).

3) Nitrogen trioxide (N₂O₃) or nitrogen sesquioxide:
Prep :  NO + NO₂ → N₂O₃
Prop.  It is anhydride of HNO₂ a weak acid.  It exists only as a pale blue solid, in pure state and melt to give a deep blue liquid. 

${\mathrm{N}}_2{\mathrm{O}}_3+{\mathrm{H}}_2\mathrm{O}⟶2{\mathrm{HNO}}_{2 }\left(\text{anhydride of }{\mathrm{HNO}}_2\right)$

${\mathrm{N}}_2{\mathrm{O}}_3+2{\mathrm{H}}_2{\mathrm{SO}}_4\to \underset{\text{Nitrosulphuric acid}}{2\mathrm{NO}{\left[{\mathrm{HSO}}_4\right]}_2}+{\mathrm{H}}_2\mathrm{O}$

Structure: 

Uses: Uses are not known.

4) Nitrogen dioxide (NO₂ or N₂O₄):

Prep.

i) $2\mathrm{NO}+{\mathrm{O}}_2⟶2{\mathrm{NO}}_2$

ii) $2\mathrm{Pb}{\left({\mathrm{NO}}_2\right)}_2⟶2\mathrm{PbO}+4{\mathrm{NO}}_2+{\mathrm{O}}_2 (\text{Lab method)}$
Prop. Highly toxic, paramagnetic, redish brown gas with choking odour and is very reactive.  Its dimeric form N₂O₄ is diamagnetic in nature.
i)  $2{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{HNO}}_2+{\mathrm{HNO}}_3$ (It is mixed anhydride of HNO₂ & HNO₃)

ii)  ${\mathrm{NO}}_2\stackrel{\mathrm{h\nu }}{\to }\mathrm{NO}+\mathrm{O}$

iii) It is combustible and supports the combustion of burning P, Mg or charcoal.  Burning S or candle is extinguished.

Structure :  Trigonal planar.

5) Nitrogen pentaoxide (N₂O₅):
Prep:   
i)   ${\mathrm{N}}_2{\mathrm{O}}_4+{\mathrm{O}}_3⟶{\mathrm{N}}_2{\mathrm{O}}_5+{\mathrm{O}}_2$        ii)   $2{\mathrm{HNO}}_3+{\mathrm{P}}_2{\mathrm{O}}_5⟶{\mathrm{N}}_2{\mathrm{O}}_5+2{\mathrm{HPO}}_3$
Prop:
i) It is a colourless crystalline solide and subslimes.
ii) ${\mathrm{N}}_2{\mathrm{O}}_5+{\mathrm{H}}_2\mathrm{O}⟶2\mathrm{H}{\mathrm{HO}}_3$ (anhydride of HNO₃)

iii) ${\mathrm{N}}_2{\mathrm{O}}_5+{\mathrm{H}}_2{\mathrm{O}}_2⟶\underset{}{\underset{\text{Pernitric acid}}{{\mathrm{HNO}}_4}+{\mathrm{HNO}}_3}$
Structure:  N – O – N bonding is present.

Uses :  As powerful oxidizing agent.

6) Phosphorous trioxide (P₂O₃ or P₄O₆):
Prep: $\begin{array}{rl}& \underset{\mathrm{white}}{{\mathrm{P}}_4}+\underset{\mathrm{limited}}{3{\mathrm{O}}_2}\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{P}}_4{\mathrm{O}}_6\end{array}$
Prop: White solid like wax, with garlic odour and highly poisonous.
Structure:

7) Phosphorous pentaoxide or flower of phosphorous (P₂O₅ or P₄O₁₀)
Prep:   $\underset{\text{(white})}{{\mathrm{P}}_4}+\underset{\text{(excess)}}{{5\mathrm{O}}_2}⟶{\mathrm{P}}_4{\mathrm{O}}_{10}$
Prop:    White crystalline solid with garlic odour and sublimes.
 ${\mathrm{P}}_2{\mathrm{O}}_5+\underset{\mathrm{cold}}{{\mathrm{H}}_2\mathrm{O}}⟶\underset{\mathrm{metaphosphoric} \mathrm{acid}}{2{\mathrm{HPO}}_3}$

Structure:

Uses :  As powerful dehydrating agent. 

Illustration 7: Which of the oxidizes N₂O₅ and P₂O₅ stronger dehydrating agent?  Give an example for the same.

Solution: P₂O₅ is stronger dehydrating agent. e.g., acidic acid on heating with P₂O₅ gives acetic anhydride with the removal of water molecular.

$2{\mathrm{CH}}_3\mathrm{COOH}\stackrel{{\mathrm{P}}_2{\mathrm{O}}_5}{\to }{\left({\mathrm{CH}}_3\mathrm{CO}\right)}_2\mathrm{O}+{\mathrm{H}}_2\mathrm{O}$

4. Formation of oxyacids:
1)  Oxyacids of N :  Nitrogen forms, number of oxyacids which are given below :

S.No.	Name	Formula	ON	Nature
i)	Nitroxylic acid	H4N2O4	+ 2	Highly explosive, difficult to get in pure state.
ii)	Nitrous acid	HNO2	+ 3	Weak acid and unstable
iii)	Nitric acid	HNO3	+ 5	Strong acid & stable
iv)	Peroxy nitric acid	HNO4	+ 5	Unstable and explosive

Nitrous acid (HNO₂) and nitric acid (HNO₃) are two important oxyacids of nitrogen & others are of less importance.
2)  Oxyacids of P:  Phosphorous form two series of oxiacids.

S.No.	Name of oxyacid	Formula	Oxidation number	Basicity
1)	Hypophosphorus acid series
i)	Hypophosphorus acid (phosphinic acid)	H3PO2	+ 1	1
ii)	Ortho Phosphorus acid (Phosphonic acid)	H3PO3	+ 3	2
iii)	Metaphosphorus acid	HPO2	+ 3	1
2)	Phosphoric series of acids.
i)	Orthophosphoric acid	H3PO4	+ 5	3
ii)	Metaphosphoric acid	HPO3	+ 5	1
iii)	Hypophosphoric acid	H4P2O6	+ 4	4
iv)	Pyrophosphoric acid	H4P2O7	+ 5	4
v)	Peroxomonophosphoric acid	H3PO5	+ 7	3

The formula of oxyacids of P can be remembered as the prefix.
Meta acid – is used for the acid obtained by the less of one water molecule.
Hypo acid is used for the acid having lower oxygen content than the parent acid.
Pyroacid is used for the acid obtained by heating two molecules with lose of one water molecule.

Trimetaphosphoric acid (HPO3)3	Polymetaphosphoric acid (HPO3)3

Arsenic form two oxyacids, arsenious acid (H₃AsO₃) and arsenic acid (H₃AsO₄).
Antimony forms one oxyacid H₃SbO₃, which exists in solutes.
Bismuth also forms one oxyacid, HBiO₃, metabismuthic acid.
In same oxidation state of element, the strength and stability of oxyacid, gradually decreases with decrease in electronegativity of central atom.         

$\underset{\text{strength or stability decreases}}{\overset{\begin{array}{llll}\mathrm{H}{\mathrm{NO}}_3 & {\mathrm{H}}_3{\mathrm{PO}}_4 & {\mathrm{H}}_3{\mathrm{AsO}}_4& {\mathrm{H}}_3{\mathrm{SbO}}_4\end{array}}{\to }}$

Some important characteristis of oxyacids of P:
i) In general, in all these oxyacids, ‘P’ has tetrahedral shape.
ii) At least one – OH group is linked to the phosphorus atom. The hydrogen atoms of – OH groups are ionizable and responsible for acidic nature.
iii)  The phosphorus series of oxyacids may have P – H bonds in addition of to P – OH bonds.  The P – H bonds are responsible for the reducing properties of the acids.
iv) Phosphoric series of oxyacids do not have P – H bonds.

Dinitrogen (N₂):
Prep:  
(i) ${\mathrm{NH}}_4\mathrm{Cl}+{\mathrm{NaNO}}_2⟶\underset{\mathrm{Ammonium}}{{\mathrm{NH}}_4{\mathrm{NO}}_2}+\mathrm{NaCl}$    
$\begin{array}{rl}& {\mathrm{NH}}_4{\mathrm{NO}}_2⟶{\mathrm{N}}_2+\underset{\text{(colle cted by downdisplacement of vater}}{2{\mathrm{H}}_2\mathrm{O}}\end{array}$
(ii) ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7⟶{\mathrm{N}}_2+{\mathrm{Cr}}_2{\mathrm{O}}_3+4{\mathrm{H}}_2\mathrm{O}$ 
(iii) $2{\mathrm{NH}}_3+3\mathrm{CuO}⟶\underset{\left(\mathrm{pure}\right)}{{\mathrm{N}}_2}+3{\mathrm{H}}_2\mathrm{O}+3\mathrm{Cu}$  
(iv) $8{\mathrm{NH}}_3+3{\mathrm{Cl}}_2⟶{\mathrm{N}}_2+6{\mathrm{NH}}_4\mathrm{Cl}$
(v) Very pure N₂ can be obtained by heating sodium or barium azides in vacuum.
$\begin{array}{l}2{\mathrm{NaN}}_3⟶2\mathrm{Na}+3{\mathrm{N}}_2\\ \\ \mathrm{Ba}{\left({\mathrm{N}}_3\right)}_2⟶\mathrm{Ca}+3{\mathrm{N}}_2+(\text{small amount)}\end{array}$

Prop:
(i) It is a colourless, odourless, tasteless, slightly lighter than air, slightly soluble in water, non poisonous gas but animals do not survive in its atmosphere due to absence of oxygen.
(ii) It is incombustible and non-supporter of combustion.
(iii) It can be liquefied to a colourless liquid (BP = – 195.8⁰C).
(iv) It is chemically inert under ordinary conditions.  However it shows chemical activity under high temperatures.
a) $\begin{array}{rl}& {\mathrm{N}}_2+{\mathrm{O}}_2\stackrel{300°\mathrm{C}}{\to }\begin{array}{rl}& \text{2NO}\end{array}\end{array}$
b) ${\mathrm{N}}_2+3{\mathrm{H}}_2\underset{\underset{200\mathrm{atm}}{{}_{400-{500}^{\circ }\mathrm{C}}}}{\overset{F{e}_0}{\to }}2{\mathrm{NH}}_3$
c) It combines with metals and non-metals to form nitrides.

d) ${\mathrm{CaC}}_2+{\mathrm{N}}_2⟶{\mathrm{CaCN}}_2+\mathrm{C} \left(\text{Nitrolim}\right)$

Uses:
i) To decrease concentration of oxygen in air and make combustion less rapid.
ii) To create inert atmosphere in certain metallurgical operations.
iii) In the manufacture of NH₃, HNO₃, CaCN₂ and other nitrogen compounds.

Active nitrogen:  When an electric discharge is allowed to pass through nitrogen under very low pressure (about 2 mm) a brilliant luminiscence is observed which persists for some time after the stop page of the discharge.  It is observed that nitrogen after the discharge is more active.  This nitrogen is termed as active nitrogen.

Ammonia (NH₃):  It is the most important hydride of nitrogen.
Prep:  i)  By heating Ammonium salts with NaOH or Ca(OH)₂ or any strong base (lab).
$\begin{array}{l}{\mathrm{NH}}_4\mathrm{Cl}+\mathrm{NaOH}⟶{\mathrm{NH}}_3+\mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O}\\ \\ 2{\mathrm{NH}}_4\mathrm{Cl}+\underset{(\mathrm{slaked} \mathrm{lime})}{\mathrm{Ca}(\mathrm{OH}{)}_2}⟶2{\mathrm{NH}}_3+{\mathrm{CaCl}}_2+2{\mathrm{H}}_2\mathrm{O}\\ \\ (2{\mathrm{NH}}_4\mathrm{Cl}+\mathrm{CaO}\stackrel{\mathrm{\Delta }}{⟶}2{\mathrm{NH}}_3+{\mathrm{CaCl}}_2+{\mathrm{H}}_2\mathrm{O})\end{array}$
ii) By heating Ammonium compounds
${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4⟶{\mathrm{NH}}_3+{\mathrm{NH}}_4{\mathrm{HSO}}_4$
iii)  By the action of NaOH on urea
${\mathrm{NH}}_2{\mathrm{CONH}}_2+2\mathrm{NaOH}⟶{\mathrm{Na}}_2{\mathrm{CO}}_3+2{\mathrm{NH}}_3$
iv)  ${\mathrm{NaNO}}_3+8\mathrm{H}\stackrel{\mathrm{Zn}/\mathrm{NaOH}}{\to }\mathrm{NaOH}+{\mathrm{NH}}_3+2{\mathrm{H}}_2\mathrm{O}$
v) Manufacturing:
a) By Haber’s Process: (discovered by German chemist Fritz Haber)
${\mathrm{N}}_2+3{\mathrm{H}}_2\to 2{\mathrm{NH}}_3+2\mathrm{kcal}$
This equation reveals that the reaction is a) a reversible reaction   b)  exothermic in forward direction and c) formation of NH₃ is followed by decrease in volume.  According to Le–Chatelier principle, optimum conditions required for the greater yield of ammonia are given below
i) Low temperature (450 – 500⁰C) and high pressure (200 atm).
ii) Catalyst:  Fe is used to speed up the slow reaction and molybdenum (M₀) is used as catalyst promoter.

Other catalysts employed are:
i) Finely divided Os or Cl.
ii) Finely divided Ni deposited over pumice stone.
iii)  Fe(OH)₃ with trace of SiO₂ and K₂O.
Impure gases poison the catalyst. Hydrogen and nitrogen used therefore, be free from CO, etc which can spoil the working of the catalyst.

Method:  Pure and dry N₂ and H₂ mixture in 1:3 ratio by volume is compressed to 200 to 300 atmospheres pressure.  Then it passes into, a catalytic chamber.  The gases, partially heated in the heat exchanger, react in the presence of the catalyst at 450 – 500⁰C in the chamber.  Ammonia is formed to the extent of about 10% in the reaction.
b) Cynamide process:  ${\mathrm{CaC}}_2+{\mathrm{N}}_2\stackrel{1000-{1100}^{\circ }\mathrm{C}}{\to }\underset{\text{Nitrolim-fertilizer}}{\underbrace{{\mathrm{CaCN}}_2 + {\mathrm{C}}_{\text{graphite}}}}$
${\mathrm{CaCN}}_2+\underset{\text{superheated steam}}{3{\mathrm{H}}_2\mathrm{O}}\stackrel{{180}^{\circ }\mathrm{C}}{\to }{\mathrm{CaCO}}_3+2{\mathrm{NH}}_3$
Now a days low temperature (500 – 600⁰C) is used under 6 – 8 atmospheric pressure.
c) From ammonical liquor: Obtained during distillation of coal.
When coal is heated to a temperature of 1000 – 1400⁰C in the absence of air iron retorts (destructive distillation) the following important products are formed.
i) Coal gas     ii)  Coaltar     iii)  Ammonical liquor and     iv)  Solid residue.
The ammoniacal liquor is treated with “milk of lime” and steam is blown through the solution.  The mixture of steam and NH₃ gas produced is absorbed in H₂SO₄.  Ammonium sulphate is formed in the solution.  (The salt is separated by crystallization and used directly as a fertilizer) alternately ammonia and steem mixture is passed through water under pressure to get a concentrated solution of ammonia.
Properties of NH₃:  i) It is a colourless gas, with a characteristic pungent odour.  It brings tears into the eyes.
ii) It is lighter than air and collected by down displacement of air.
iii)  It is a strong base and it is highly soluble in water due to H-bonding.
iv) It has higher M.P. and B.P. in comparison to other hydrides of V group due to H-bonding.
Chemical properties:
i) It is highly stable but decomposes on heating, into nitrogen and hydrogen.
$2{\mathrm{NH}}_3\underset{\mathrm{on} \mathrm{electic} \mathrm{spark}}{\overset{∆}{\to }}{\mathrm{N}}_2+3{\mathrm{H}}_2$
ii) Ordinary, ammonia is neither combustible nor a supporter of combustion. However, it burn in the presence of oxygen to form nitrogen and water.
$4{\mathrm{NH}}_3+3{\mathrm{O}}_2⟶2{\mathrm{N}}_2+6{\mathrm{H}}_2\mathrm{O}$
iii) It is a Lewis base in nature & forms salts with acids.
${\mathrm{NH}}_3+\mathrm{HCl}⟶{\mathrm{NH}}_4\mathrm{Cl} \text{(thick white fumes)}$
iv) It oxidise to nitrogen when passed over heated CuO or PbO.
$3\mathrm{CuO}+2{\mathrm{NH}}_3⟶3\mathrm{Cu}+{\mathrm{N}}_2+3{\mathrm{H}}_2\mathrm{O}$
$3\mathrm{PbO}+{\mathrm{ZNH}}_3⟶3\mathrm{Pb}+{\mathrm{N}}_2+3{\mathrm{H}}_2\mathrm{O}$
Both chlorine and bromine oxidise ammonia.
$\begin{array}{rl}& 8{\mathrm{NH}}_3+3{\mathrm{Cl}}_2⟶{\mathrm{N}}_2+6{\mathrm{NH}}_4\mathrm{Cl}\\ & \text{(excess)}\\ & \\ & \begin{array}{c}{\mathrm{NH}}_3+\underset{\text{(excess)}}{3{\mathrm{Cl}}_2⟶}\underset{\text{(explosive)}}{{\mathrm{NCl}}_3}+3\mathrm{HCl}\\ \\ 2{\mathrm{NH}}_3+3{\mathrm{I}}_2⟶\underset{\begin{array}{c}\text{dakk brown ppt}\\ \text{(explode on drying)}\end{array}}{{\mathrm{NH}}_3{\mathrm{NI}}_3}\end{array}\end{array}$
Hypochlorites and hypobromides oxidise ammonia to nitrogen
$2{\mathrm{NH}}_3+3\mathrm{NaClO}⟶{\mathrm{N}}_2+3\mathrm{NaCl}+3{\mathrm{H}}_2\mathrm{O}$
Bleaching powder is also oxidise ammonia on warming.
$2{\mathrm{NH}}_3+3{\mathrm{CaOCl}}_2⟶3{\mathrm{CaCl}}_2+{\mathrm{N}}_2+3{\mathrm{H}}_2\mathrm{O}$
Thus, ammonia acts as a reducing agent.
v) When dry ammonia is passed over heated sodium or potassium amides are formed with the liberation of hydration.
$2\mathrm{Na}+\underset{\text{(dry)}}{2{\mathrm{NH}}_3}⟶\underset{\text{(sodamide)}}{2{\mathrm{NaNH}}_2}+{\mathrm{H}}_2$
vi) Aqueous ammonia on reaction with metal salts, forms metal hydroxides and complex compounds.
$$\begin{gathered} \underset{\text{salt}}{{\mathrm{FeCl}}_3}+\underset{\text{(aqammonia)}}{{\mathbf{3}\mathbf{NH}}_4\mathrm{OH}}\underset{\text{ppt}}{⟶\mathrm{Fe}(\mathrm{OH}{)}_3}+3{\mathrm{NH}}_4\mathrm{Cl} \\ {\mathrm{ACl}}_3+3{\mathrm{NH}}_4\mathrm{OH}⟶\underset{\mathrm{ppt}}{\mathrm{Al}\left(\mathrm{OH}\right)}+3{\mathrm{NH}}_4\mathrm{Cl} \\ {\mathrm{CuSO}}_4+2{\mathrm{NH}}_4\mathrm{OH}⟶\underset{\text{Blue})}{\mathrm{Cu}(\mathrm{OH}{)}_2}+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\stackrel{2{\mathrm{NH}}_4\mathrm{OH}}{\to }\underset{\text{Tetramine copper sulphate (deep blue solution)}}{\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4+4{\mathrm{H}}_2\mathrm{O}} \\ {\mathrm{CrCl}}_3+3{\mathrm{NH}}_4\mathrm{OH}⟶\underset{\mathrm{ppt}}{\mathrm{Cr}(\mathrm{OH}{)}_3}+3{\mathrm{NH}}_4\mathrm{Cl} \\ \begin{array}{rl}& \mathrm{AgCl}+2{\mathrm{NH}}_4\mathrm{OH}⟶\underset{\begin{array}{rl}& \text{Diamine silver chloride}\end{array}}{\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]\mathrm{Cl}}+2{\mathrm{H}}_2\mathrm{O}\\ & {\mathrm{ZnSO}}_4+2{\mathrm{NH}}_4\mathrm{OH}⟶\mathrm{Zn}(\mathrm{OH}{)}_2+{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\stackrel{2{\mathrm{NH}}_4\mathrm{OH}}{\to }\underset{\mathrm{Tetramine} \mathrm{zinc} \mathrm{sulphate}}{\left[\mathrm{Zn}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4}+4{\mathrm{H}}_2\mathrm{O}\\ & {\mathrm{CdSO}}_4+4{\mathrm{NH}}_4\mathrm{OH}⟶\underset{(\mathrm{colourless} \mathrm{so} \mathrm{In})}{\underset{\mathrm{cadmiumtetra} \mathrm{mine} \mathrm{sulphate}}{\left[\mathrm{Cd}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4}}+4{\mathrm{H}}_2\mathrm{O}\\ & {\mathrm{NiCl}}_2+2{\mathrm{NH}}_4\mathrm{OH}⟶\underset{\mathrm{green} \mathrm{ppt}}{\mathrm{Ni}(\mathrm{OH}{)}_2}+2{\mathrm{NH}}_4\mathrm{Cl}\stackrel{4{\mathrm{NH}}_4\mathrm{OH}}{\to }\left[\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_6\right]{\mathrm{Cl}}_2+6{\mathrm{H}}_2\mathrm{O}\end{array} \end{gathered}$$

$$\begin{gathered} \underset{}{\underset{\text{(Ous)}}{{\mathrm{Hg}}_2{\mathrm{Cl}}_2}+2{\mathrm{NH}}_4\mathrm{OH}⟶}\underset{\text{grey ppt}}{\underbrace{\mathrm{Hg} + {\mathrm{HgNH}}_2\mathrm{Cl}}}+{\mathrm{NH}}_4\mathrm{Cl}+2{\mathrm{H}}_2\mathrm{O} \\ {\mathrm{HgCl}}_2+2{\mathrm{NH}}_4\mathrm{OH}⟶\underset{\text{Amidomercuric chloride}}{{\mathrm{HgNH}}_2\mathrm{Cl}}+{\mathrm{NH}}_4\mathrm{Cl}+2{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

vii)  $\begin{array}{c}\underset{\text{Nessler’s reagent}}{\underbrace{2{\mathrm{K}}_2{\mathrm{Hgl}}_4+3\mathrm{KOH}}}+\stackrel{{\mathrm{NH}}_3}{\to }\underset{\begin{array}{c}\text{iodide of millon’s base}\\ \text{(redish brown ppt)}\end{array}}{{ \mathrm{NH}}_2\mathrm{HgOHgl}\text{(Test of }{\mathrm{NH}}_3)}\end{array}$  

Uses of NH₃:
i) As refrigerant
ii) In the manufacture of sodium bicarbonate (solvay process), nitric acid (ostwald’s process) ammonium compounds e.g., – ammonium nitrate in used in certain explosives and ammonium sulphate, ammonium calcium phosphate, ammonium calciumnitrate urea etc are used as fertilizers. Urea is an excellent fertilizer of Nitrogen.
iii)   As cleansing agent for removing grease.
iv) In the preparation of rayon and artificial silk.
v) As a good solvent (liq NH₃) for both ionic as well as covalent compounds.

Drying of NH₃: Moist NH₃ can not be dried by usual drying agents like conc. H₂SO₄; fused CaCl₂ is P₂O₅ as they react with NH₃.  Dry quick lime is useful agent to dry NH₃ as it does not react with NH₃.

Illustration 8: What is the function of CaCl₂ in cyanamide process?
Solution: Function of CaCl₂ in cyanamide process is as catalyst.

Illustration 9: How do you convert NH₄NO₃ into NH₃?
Solution: By treating NH₄NO₃ with strong base like NaOH.
${\mathrm{NH}}_4{\mathrm{NO}}_3+\mathrm{NaOH}⟶{\mathrm{NaNO}}_3+{\mathrm{NH}}_3+{\mathrm{H}}_2\mathrm{O}$

Illustration 10: Why conc. H₂SO₄ cannot be used to dry ammonia?
Solution: For drying of ammonia gas, the dehydrating agent sulphuric acid cannot be used as it reacts with ammonia as follows.
$2{\mathrm{NH}}_3+{\mathrm{H}}_2{\mathrm{SO}}_4⟶{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$

Ammonium chloride (NH₄Cl):  It is also known as salammoniac.
Prep. ${\mathrm{NH}}_3+\mathrm{HCl}⟶{\mathrm{NH}}_4\mathrm{Cl}$

Prop. It is white crystalline solid highly soluble in water and decomposes at a high temperature.
$\begin{array}{c}\\ \underset{\left(\mathrm{Volatiosalt}\right)}{{\mathrm{NH}}_4\mathrm{Cl}}\end{array}{\stackrel{\text{decom poses at at high teperature}}{\to }\mathrm{NH}}_3+\mathrm{HCl}$

Uses:

1)  In, soldering, tenning, making of drycells, dyeing, calicoprinting and in medicine.
2)  As laboratory reagent.
Ammonium nitrate (NH₄NO₃):
Prep:   ${\mathrm{NH}}_3+\underset{60\mathrm{\%}}{\mathrm{HNO}}⟶{\mathrm{NH}}_4{\mathrm{NO}}_3$
Prop.    It is a colourless, deliquescent, explosive solid.  It is highly soluble in water.  On gentle heating it decomposes as
${\mathrm{NH}}_4{\mathrm{NO}}_3⟶{\mathrm{N}}_2\mathrm{O}+2{\mathrm{H}}_2\mathrm{O}$
On rapid heating it explodes
$2{\mathrm{NH}}_4{\mathrm{NO}}_3⟶2{\mathrm{N}}_2+{\mathrm{O}}_2+4{\mathrm{H}}_2\mathrm{O}$

Uses: For making explosives such as
Amatol: ${\mathrm{NH}}_4{\mathrm{NO}}_3\left(80\mathrm{\%}\right)+\mathrm{TNT}\left(20\mathrm{\%}\right)$
Ammonal : ${\mathrm{NH}}_4{\mathrm{NO}}_4+\text{Alpowder}\text{( small quantity)}$
Nitrous acid (HNO₂):
The free acid is unknown.  It is known only in solution.
Prep:   
i) ${\mathrm{N}}_2{\mathrm{O}}_3+\underset{(\text{cold)}}{{\mathrm{H}}_2\mathrm{O}}\to 2{\mathrm{NHO}}_2$

ii)  $\mathrm{Ba}{\left({\mathrm{NO}}_2\right)}_2+\underset{\left(\mathrm{dil}\right)}{{\mathrm{H}}_2{\mathrm{SO}}_4}⟶{\mathrm{BaSO}}_4\downarrow +2{\mathrm{HNO}}_2$

iii)  $2{\mathrm{NaNO}}_2+\underset{\mathrm{dil}}{2\mathrm{HCl}}⟶2{\mathrm{HNO}}_2+2\mathrm{NaCl}$

iv)  ${\mathrm{NH}}_3+2{\mathrm{H}}_2{\mathrm{O}}_2⟶{\mathrm{HNO}}_2+4{\mathrm{H}}_2\mathrm{O}$

Prop: Its aqueous solution is pale blue in colour due to presence of N₂O₃ (anhydride).
Its aqueous solution is unstable and decomposes on heating.

$\begin{array}{rl}& \underset{\left(\text{cold}\right)}{3{\mathrm{HNO}}_2}\underset{oxide}{\overset{auto}{\to }}2\mathrm{NO}+{\mathrm{HNO}}_3+{\mathrm{H}}_2\mathrm{O}\\ & 2{\mathrm{HNO}}_2\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{H}}_2\mathrm{O}+{\mathrm{N}}_2{\mathrm{O}}_3\to \mathrm{NO}+\underset{Brown}{{\mathrm{NO}}_2}\end{array}$

It behaves as both oxidizing and reducing agent.
1) Oxidising properties:
$2{\mathrm{HNO}}_2⟶{\mathrm{H}}_2\mathrm{O}+2\mathrm{NO}+\left[\mathrm{O}\right]$
i) ${\mathrm{SO}}_2+2{\mathrm{HNO}}_2⟶{\mathrm{H}}_2{\mathrm{SO}}_4+2\mathrm{NO}$

ii) ${\mathrm{H}}_2\mathrm{S}+2{\mathrm{HNO}}_2⟶\mathrm{S}+2{\mathrm{H}}_2\mathrm{O}+\mathrm{NO}$

iii) $2\mathrm{Kl}+{\mathrm{H}}_2{\mathrm{SO}}_4+2{\mathrm{HNO}}_2⟶{\mathrm{K}}_2{\mathrm{SO}}_4+2\mathrm{NO}+{\mathrm{I}}_2+{\mathrm{TH}}_2\mathrm{O}$

iv) ${\mathrm{SnCl}}_2+2\mathrm{HCl}+2{\mathrm{HNO}}_2⟶{\mathrm{SnCl}}_4+2\mathrm{NO}+2{\mathrm{H}}_2\mathrm{O}$

v) $2{\mathrm{FeSO}}_4+{\mathrm{H}}_2{\mathrm{SO}}_4+2{\mathrm{HNO}}_2⟶{\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3+2\mathrm{NO}+{\mathrm{H}}_2\mathrm{O}$

2) Reducing properties:
${\mathrm{HNO}}_2+\mathrm{O}⟶{\mathrm{HNO}}_3$

i)  ${\mathrm{Br}}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{HNO}}_2⟶2\mathrm{HBr}+{\mathrm{HNO}}_3$

ii)  $2{\mathrm{KMnO}}_4+3{\mathrm{H}}_2{\mathrm{SO}}_4+5{\mathrm{HNO}}_2⟶{\mathrm{K}}_2{\mathrm{SO}}_4+2{\mathrm{MnSO}}_4+5{\mathrm{HNO}}_3+3{\mathrm{H}}_2\mathrm{O}$

iii)  ${\mathrm{H}}_2{\mathrm{O}}_2+{\mathrm{HNO}}_2⟶{\mathrm{HNO}}_3+{\mathrm{H}}_2\mathrm{O}$

iv)  ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+4{\mathrm{H}}_2{\mathrm{SO}}_4+3{\mathrm{HNO}}_2⟶{\mathrm{K}}_2{\mathrm{SO}}_4+{\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3+3{\mathrm{HNO}}_3+4{\mathrm{H}}_2\mathrm{O}$

3) It reacts with anomonia to from nitrogen and water.

${\mathrm{NH}}_3+{\mathrm{HNO}}_2⟶{\mathrm{N}}_2+{\mathrm{H}}_2\mathrm{O}$

4) It decomposes urea and other aliphatic primary amines to nitrogen.

$$\begin{gathered} \underset{urea}{{\mathrm{NH}}_2{\mathrm{CONH}}_2}+2{\mathrm{HNO}}_2⟶2{\mathrm{N}}_2+{\mathrm{CO}}_2+3{\mathrm{H}}_2\mathrm{O} \\ {\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_2+{\mathrm{HNO}}_2⟶\underset{(\mathrm{Ethyl} \mathrm{alcohol})}{{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}}+{\mathrm{N}}_2+{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

With aromatic primary amines, in presence of HCl at 0 to 5⁰C, it forms diazonium salts.

$\begin{array}{rl}& {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2+\mathrm{HCl}+{\mathrm{HNO}}_2\stackrel{0-5^{\circ }\mathrm{C}}{\to } \underset{\text{(Bevueredämiun dibida)}}{{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{N}=\mathrm{NCl}}+2{\mathrm{H}}_2\mathrm{O}\end{array}$

Structure:  Since HNO₂ forms two types of organic compound, the nitrites (R – ONO) and nitro compounds (R – NO₂), it is considered to be tautomeric mixture of two forms.
Uses:
i) In organic chemistry in the preparation of diazo compounds which are employed for making aniline dyes.
ii) As oxidizing and reducing agent in analytical chemistry.
iii)  For the replacement of – NH₂ group by – OH group in diphatic primary amines.         

Nitric acid (HNO₃): It is also known as aquafortis
Preparation:
1) Lab Method:  By distilling nitre with conc. H₂SO₄.

$2{\mathrm{NaNO}}_3+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{conc}\right)⟶{\mathrm{Na}}_2{\mathrm{SO}}_4+2{\mathrm{HNO}}_3$

2) Industrial Method:
a) Birk land – Eyde process – or Arc process (old):
Air free from CO₂ and moisture is passed through arc at 3000⁰C, ‘NO’ is formed; No oxidise to NO₂ which is absorbed in water in the presence of air to give HNO₃.

$\begin{array}{l}{\mathrm{N}}_2{\mathrm{O}}_2⟶2\mathrm{NO}\\ \\ 2\mathrm{NO}+{\mathrm{O}}_2⟶2{\mathrm{NO}}_2\\ \\ 4{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2⟶4{\mathrm{HNO}}_3\end{array}$

b) Ostwald’s process:

$\begin{array}{l}4{\mathrm{NH}}_3+5{\mathrm{O}}_2\underset{{800}^{\circ }\mathrm{C}}{\overset{\mathrm{Pt} \mathrm{gauge}}{\to }}4\mathrm{NO}+6{\mathrm{H}}_2\mathrm{O}\\ \\ 2\mathrm{NO}+{\mathrm{O}}_2⟶2{\mathrm{NO}}_2\\ \\ 4{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2⟶\underset{(50-60\mathrm{\%})}{4{\mathrm{HNO}}_3\left(\mathrm{dil}\right)}\\ \end{array}$

Concentration of HNO₃:
${\mathrm{HNO}}_3(50-60\mathrm{\%})\underset{\text{with conc }{\mathrm{H}}_2{\mathrm{SO}}_4}{\overset{\text{disfillation}}{\to }} {\mathrm{HNO}}_3\left(92\mathrm{\%}\right) \underset{\text{feezing mixture}}{\overset{\text{Cooling in}}{\to }}\text{colou rless crystals}\underset{100\%}{\stackrel{melt}{\to }{\mathrm{HNO}}_3}$

Physical properties:
i) It is anhydrous colourless, syrupy, pungent liquid usually available as 68% and 15.7M.
ii) BP = 84.1⁰C, FP = – 42⁰C
iii) It’s aqueous solution is often yellow due to the presence of small concentration of NO₂.
iv) HNO₃ containing NO₂, is called fuming nitric acid. It is brown (yellow) in colour and obtained by distilling conc. HNO₃ with a little starch.
v) It has extremely corrosive action on skin and causes painful sores.

Chemical properties: 
i) Acidic nature: It is a strong acid and in aqueous solution the ionization is virtually completed.
${\mathrm{HNO}}_3+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{NO}}_3^{-}$
Thus, it reacts with basic oxides, hydroxides, carbonates, bicarbonates etc to form corresponding salts.
$\begin{array}{l}\mathrm{CaO}+2{\mathrm{HNO}}_3⟶\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}\\ \\ {\mathrm{Na}}_2{\mathrm{CO}}_3+{\mathrm{HNO}}_3⟶2{\mathrm{NaNO}}_3+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2\end{array}$
ii) Oxidising nature: (strong oxidizing agent)
$\begin{array}{l}\underset{\text{conc}}{2{\mathrm{HNO}}_3}⟶{\mathrm{H}}_2\mathrm{O}+2{\mathrm{NO}}_2+\left[\mathrm{O}\right]\\ \\ \underset{\mathrm{dl}}{{\mathrm{HHO}}_3}⟶{\mathrm{H}}_2\mathrm{O}+2\mathrm{NO}+3\left(\mathrm{O}\right)\end{array}$

i) Reaction with non metals: (oxidation of non-metals)
$\begin{array}{rl}& (2{\mathrm{HNO}}_3⟶{\mathrm{H}}_2\mathrm{O}+2{\mathrm{NO}}_2+\mathrm{O})\\ & \\ & \mathrm{S}+\underset{\text{hot \& Conc}}{6{\mathrm{HNO}}_3}⟶\underset{}{\underset{\text{sulphunic add}}{{\mathrm{H}}_2{\mathrm{SO}}_4}+6{\mathrm{NO}}_2}+2{\mathrm{H}}_2\mathrm{O}\\ & \\ & \mathrm{C}+4{\mathrm{HNO}}_3⟶\underset{}{\underset{\text{carbonic acid}}{{\mathrm{H}}_2{\mathrm{CO}}_3}+4{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}}\\ & {\mathrm{I}}_2+1{\mathrm{OHNO}}_3⟶\underset{\text{lodic acid}}{2{\mathrm{HIO}}_3}+10{\mathrm{NO}}_2+4{\mathrm{H}}_2\mathrm{O}\end{array}$

ii) Reaction with compounds: (oxidation of compounds):

$\begin{array}{rl}& (2{\mathrm{HNO}}_3⟶{\mathrm{H}}_2\mathrm{O}+2{\mathrm{NO}}_2+[\mathrm{O}\left]\right)\\ & \\ & {\mathrm{SO}}_2+2{\mathrm{HNO}}_3⟶{\mathrm{H}}_2{\mathrm{SO}}_4+2{\mathrm{NO}}_2\\ & \\ & {\mathrm{H}}_2\mathrm{S}+2{\mathrm{HNO}}_3⟶\mathrm{S}+2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{NO}}_2\\ & \\ & {\mathrm{FeSO}}_4+3{\mathrm{H}}_2{\mathrm{SO}}_4+2{\mathrm{HNO}}_3⟶3{\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3+\underset{\mathrm{Nitrosoferrous} \mathrm{sulphate}}{\underset{({\mathrm{FeSO}}_4\cdot \mathrm{NO})}{\underset{\downarrow {\mathrm{FeSO}}_4}{2\mathrm{NO}}}}+4{\mathrm{H}}_2\mathrm{O}\\ & \mathrm{KI}+8{\mathrm{HNO}}_3⟶6{\mathrm{KNO}}_3+2\mathrm{NO}+3{\mathrm{I}}_2+4{\mathrm{H}}_2\mathrm{O}\\ & \\ & \begin{array}{l}\mathrm{FeS}+8{\mathrm{HNO}}_3⟶{\mathrm{FeSO}}_4+8{\mathrm{NO}}_2+4{\mathrm{H}}_2\mathrm{O}\\ \\ \underset{}{\underset{\mathrm{or} \mathrm{HI}}{\mathrm{HBr}}+2{\mathrm{HNO}}_3}⟶{\mathrm{Br}}_2+2{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}\end{array}\end{array}$

iii) Reactions with metals: Armstrong’s theory:  Most of the metals are attached by nitric acid except noble metals like gold and platinum.  According to Aranstroug’s theory, the metals first displaces nascent hydrogen from acid which further reacts with the nitric acid to give secondary reactions.

$$\begin{gathered} \underset{\text{(aboveHisoelectrochemical series)}}{\text{Metal}+{\mathrm{HNO}}_3}⟶\text{Metalnitrate}+\underset{\mathrm{Re}\text{duce}{\mathrm{HNO}}_3}{\underset{\downarrow }{\mathrm{H}}} \text{Primary reaction}) \\ \begin{array}{l}2{\mathrm{HNO}}_3+2\mathrm{H}⟶{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O} \text{(secondar reaction)}\\ \\ 2{\mathrm{HNO}}_3+6\mathrm{H}⟶\mathrm{NO}+4{\mathrm{H}}_2\mathrm{O}\\ \\ 2{\mathrm{HNO}}_3+8\mathrm{H}⟶{\mathrm{N}}_2\mathrm{O}+5{\mathrm{H}}_2\mathrm{O}\\ \\ {2\mathrm{HNO}}_3+10\mathrm{H}⟶{\mathrm{N}}_2+6{\mathrm{H}}_2\mathrm{O}\end{array} \end{gathered}$$

Factors affecting the secondary reactions:      
i) Nature of the metal
ii) Concentration of the acid
iii)  Temperature
iv) presence of impurities

A) Reaction with metals which lies above hydrogen in electrochemical series:
i) Reactions with ‘Zn’ under different conditions:
a) With cold and very dil nitric acid.
$4\mathrm{Zn}+\underset{(\mathrm{V}.\mathrm{dil})6\mathrm{\%}}{1{\mathrm{OHNO}}_3}⟶4\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{NH}}_4{\mathrm{NO}}_3+3{\mathrm{H}}_2\mathrm{O}$

b) With cold and dil HNO_{3
$4\mathrm{Zn}+\underset{\left(\mathrm{di}120\mathrm{\%}\right)}{10{\mathrm{HNO}}_3}⟶4\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{N}}_2\mathrm{O}+5{\mathrm{H}}_2\mathrm{O}$}

c) With cold and moderately conc HNO_{3
$3\mathrm{Zn}+8{\mathrm{HNO}}_3⟶3\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+4{\mathrm{H}}_2\mathrm{O}+2\mathrm{NO}$}

d) With cold & conc HNO_{3
$\mathrm{Zn}+\underset{\left(\text{cold}\mathrm{\&}\text{conc}\right)}{4{\mathrm{HNO}}_3}⟶\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}$}

ii) Reactions with iron under different conditions:

$\begin{array}{l}\underset{\mathrm{v}\text{.dil}}{4\mathrm{Fe}+10{\mathrm{HNO}}_3}⟶4\mathrm{Fe}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{NH}}_4{\mathrm{NO}}_3+3{\mathrm{H}}_2\mathrm{O}\\ \\ 4\mathrm{Fe}+\underset{\mathrm{dil}}{10{\mathrm{HNO}}_3}⟶4\mathrm{Fe}{\left({\mathrm{NO}}_3\right)}_2+\underset{\text{Nitrous oxide}}{{\mathrm{N}}_2\mathrm{O}}+5{\mathrm{H}}_2\mathrm{O}\\ \\ \mathrm{Fe}+\underset{\mathrm{conc}}{6{\mathrm{HNO}}_3}⟶\underset{\mathrm{Ferricnitrate}}{\mathrm{Fe}{\left({\mathrm{NO}}_3\right)}_3}+3{\mathrm{NO}}_2+3{\mathrm{H}}_2\mathrm{O}\end{array}$

Iron is rendered passive by highly concentrated nitric acid (80%).

iii) Reactions with Tin:

$$\begin{gathered} 4\mathrm{Sn}+\underset{\text{(dii)}}{1{\mathrm{OHNO}}_3}⟶\underset{\mathrm{stannous} \mathrm{nitrate}}{4\mathrm{Sn}{\left({\mathrm{NO}}_3\right)}_2}+{\mathrm{NH}}_4{\mathrm{NO}}_3+3{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Sn}+\underset{\text{(Hot, conc})}{{4\mathrm{HNO}}_3}⟶\underset{\text{metastan nic acid}}{{\mathrm{H}}_2{\mathrm{SnO}}_3}+4{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

iv) Reaction with lead:

$\begin{array}{l}3\mathrm{Pb}+\underset{\text{dil})}{8{\mathrm{HNO}}_3}⟶3\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NO}+4{\mathrm{H}}_2\mathrm{O}\\ \\ \mathrm{Pb}+\underset{\mathrm{Conc}.}{4{\mathrm{HNO}}_3}⟶\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}\end{array}$

v) Metals like Mg and Mn give hydrogen with dil HNO₃:

$\begin{array}{l}\mathrm{Mg}+\underset{\left(\mathrm{dil}\right)}{{2\mathrm{HNO}}_3}⟶\mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\\ \\ \mathrm{Mn}+\underset{\left(\text{dil}\right)}{{2\mathrm{HNO}}_3}⟶\mathrm{Mn}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\end{array}$

Passivity:  Metals like, Fe, Cr, Ni, Al or Co become inactive or passive by the action of conc. HNO₃, due to stable oxide layer.

B) Reaction with metals lies below hydrogen in the electrochemical series:
i) Reaction with copper under different conditions:
a) With cold and dil HNO₃;
$3\mathrm{Cu}+8{\mathrm{HNO}}_3⟶3\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+2\mathrm{NO}+2{\mathrm{H}}_2\mathrm{O}$

b) With cold and moderately conc. HNO_{3
$3\mathrm{Cu}+8{\mathrm{HNO}}_3⟶3\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+4{\mathrm{H}}_2\mathrm{O}+2\mathrm{NO}$}

c) With cold and conc. HNO_{3
$\mathrm{Cu}+\underset{\text{hot, conc}}{4{\mathrm{HNO}}_3}⟶\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}$}

d) With hot and conc. HNO_{3
$5\mathrm{Cu}+12{\mathrm{HNO}}_3⟶5\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+6{\mathrm{H}}_2\mathrm{O}+{\mathrm{N}}_2$}

(Silver behaves like copper)
$$\begin{gathered} 3\mathrm{Ag}+\underset{\left(\mathrm{dil}\right)}{4{\mathrm{HNO}}_3}⟶3\mathrm{Ag}{\left({\mathrm{NO}}_3\right)}_2+\mathrm{NO}+2{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Ag}+\underset{\text{(conc})}{2{\mathrm{HNO}}_3}⟶{\mathrm{AgNO}}_3+{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

ii) Reactions with mercury:

a) With dil HNO_{3
$6\mathrm{Hg}+\underset{\text{(dil)}}{8{\mathrm{HNO}}_3}⟶\underset{\mathrm{Mercurous} \mathrm{acid}}{3\mathrm{Hg}{\left({\mathrm{NO}}_3\right)}_2}+2\mathrm{NO}+4{\mathrm{H}}_2\mathrm{O}$}

b) With conc. HNO_{3
$\mathrm{Hg}+4\underset{\text{(conc})}{{\mathrm{HNO}}_3}⟶\underset{\text{(Mercuic nitrate})}{\mathrm{Hg}{\left({\mathrm{NO}}_3\right)}_2}+2{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}$}

 Summary:

Conc. of HNO3	Metals	Main products
Very dil. HNO3	Mg, Mn	Metal nitrate + H2
	Fe, Zn, Sn	Metal nitrate + NH4NO3
Dil. HNO3	Pb, Cu, Ag, Hg	Metal nitrate + NO
	Fe, Zn	Metal nitrate + N2O
	Sn	Metal nitrate + N2O
Conc. HNO3	Zn, Fe, Pb, Cu, Ag	Metal nitrate + NO2
	Sn	Metastanic acid (H2SnO3) + NO2

4) Reactions with metalloids:  Forms highest oxyacids like non-metal.
$$\begin{gathered} \underset{\text{(hot, conc)}}{2\mathrm{As}+10{\mathrm{HNO}}_3}⟶\underset{\left(\text{arsenic acid}\right)}{2{\mathrm{H}}_3{\mathrm{AsO}}_4+10{\mathrm{NO}}_2}+2{\mathrm{H}}_2\mathrm{O} \\ \underset{}{\underset{\text{(oxidise)}}{\mathrm{Sb}}+\underset{(\mathrm{conc}. \mathrm{hot})}{5{\mathrm{HNO}}_3}}⟶\underset{\mathrm{antimonic} \mathrm{acid}}{{\mathrm{H}}_3{\mathrm{SbO}}_4}+5{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

5) Reaction with organic compounds:
i) Nitration:

$\begin{array}{rl}& \stackrel{}{\underset{{\mathrm{CH}}_2\mathrm{OH}}{\overset{{\mathrm{CH}}_2\mathrm{OH}}{\underset{\left|}{\overset{\right|}{\mathrm{CHOH}}}}}+3{\mathrm{HNO}}_3}\stackrel{}{\underset{<{25}^{\circ }\mathrm{C}}{\overset{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }}}\underset{\text{(Trinitroglycerine)}}{\underset{{\mathrm{CH}}_2{\mathrm{ONO}}_2}{\stackrel{{\mathrm{CH}}_2{\mathrm{ONO}}_2}{\underset{\left|}{\overset{\right|}{{\mathrm{CHONO}}_2}}}}}+3{\mathrm{H}}_2\mathrm{O}\\ & \end{array}$

ii) Oxidation:

Structure:

Uses:
i) In manufacturing of fertilizers & explosives like TNT, picric acid, nitroglycerine, dynamite etc.
ii) In the manufacture of artificial silk, dyes, drugs etc.
iii)  In purification of silver and gold.
iv) In the preparation of aqua regia.
v) As laboratory regent.
vi) As oxidizing agent.
vii)  As nitrating reagent etc.

Illustration 11: What are the anhydrides of nitrous and nitric acids?
Solution: N₂O₃ is the anhydride of nitrous acid and N₂O₅ is the anhydride of nitric acid.

Illustration 12: HNO₃ acts only as an oxidizing agent while nitrous HNO₂ acid can act as both an oxidising and a reducing agents.  Explain.
Solution: In HNO₃, N–exhibit + 5 oxidation state (maximum) whereas in HNO₂, N-exhibits + 3 oxidation state, which can be raised as well as lowered.  So, HNO₃ can act only as an oxidizing agent while HNO₂ can act as both an oxidising and a reducing agents.

Phosphorous: (P₄): (Greek word, phos = light, phoro = I carry) 
Extraction: Phosphorus is extracted either from phosphorite or bone ash by the application of following two processes.
i) Retort process (old process)
ii) Electrothermal process (Modern process)
i) Retort process: Bone ash or phosphorite mineral is digest with concentrated H₂SO₄ (60%) orthophosphoric acid is formed, which is changed into metaphosphoric acid.  Metaphosphoric acid is mixed with powdered coke and distilled in fireclay retorts.  The acid is reduced to phosphorus by carbon which comes in vaporized form the vapours are condensed below water.

$$\begin{gathered} {\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2+3{\mathrm{H}}_2{\mathrm{SO}}_4⟶3{\mathrm{CaSO}}_4+2{\mathrm{H}}_3{\mathrm{PO}}_4 \\ {\mathrm{H}}_3{\mathrm{PO}}_4⟶\underset{\text{(metaphosphoric acid)}}{{\mathrm{HPO}}_3}+{\mathrm{H}}_2\mathrm{O} \\ 4{\mathrm{HPO}}_3+10\mathrm{C}⟶{\mathrm{P}}_4+10\mathrm{CO}+2{\mathrm{H}}_2\mathrm{O} \end{gathered}$$

ii) By electrothermal process (modern):
Bone-ash or powdered mineral phosphate is mixed with silica and coke and the mixture is heated in an electric furnace at 1400 to 1500⁰C.  Phosphorus vapours so evolved are passed through water then solid phosphorus is obtained               

$2{\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2+6{\mathrm{SiO}}_2+10\mathrm{C}⟶6{\mathrm{CaSiO}}_3+\underset{\left(\text{white}\right)}{P_4}+10\mathrm{CO}$

Purification:  By melting under acidified solution of K₂Cr₂O₇.  The impurities are oxidized and redistilled.
Allotropic modification of phosphorus:  It’s important allotropes are white and red.
White phosphorus (yellow):  Freshly prepared phosphorus is colourless.  On standing it acquires pale lemone colour due to formation of red variety.  It is therefore called yellow phosphorus.  Due to its poisonous nature the jaw bone start decay and diseases is known as “phossy Jaw”.
By heating in an inert atmosphere at 240 – 250⁰C, it changes into red phosphorus.

$\text{Yellow }{\mathrm{P}}_4\underset{\text{inert atm}}{\overset{240-{250}^{\circ }\mathrm{C}}{\to }} \text{Red }\mathrm{P}$

Structure: 

Since the hybridization of P in P₄ is sp³, the % of p-character is 75%.

Uses : As rat poison.

Red phosphorus:  It is an odourless, non-poisonous, dark red powder.
It is prepared by carefully heating yellow phosphorus in an inert atmosphere for about 8 days.

$\text{Yellow }{\mathrm{P}}_4\underset{\text{inertation}}{\overset{240-{250}^{\circ }\mathrm{C}}{\to }} \text{Red }\mathrm{P}$

It changes to white (yellow) phosphorus when it is vaporized and vapours are condensed.

$\mathrm{Red} P\underset{\text{Inert atom}}{\overset{{550}^{\circ }\mathrm{C}}{\to }} \text{Vapours}\stackrel{\mathrm{condense}}{\to }\text{white }\mathrm{P}$

Structure:  Polymeric structure.

Scarlet phosphorus: It is prepared by heating PBr₃ with Hg at 240⁰C.

$4{\mathrm{PBr}}_3+6\mathrm{Hg}⟶6{\mathrm{HgBr}}_2+\underset{(\text{Scarlet)}}{{\mathrm{P}}_4}$

Black phosphorus:  It is prepared by heating white P at 200⁰C.  It is the most stable forms and good conductor of electricity.

Comparison between white and red phosphorus:

	Property	White P	Red P
1.	Physical state	Soft waxy solid	Brittle powder
2.	Colour	White in pure state and become yellow on standing	Red
3.	Odour	Garlic	Odourless
4.	Specific gravity	1.8	2.1
5.	M.P.	440C	Sublimes in absence of air at 2900C
6.	Ignition temperature	Low, 300C	High, 2600C
7.	Solubility in water	Insoluble	Insoluble
8.	Solubility & in CS2, Cl4, benzene	Soluble	Insoluble
9.	Physiological action	Poisonous	Non-poisonous
10.	Chemical activity	Very active	Less active
11.	Phosphores cence	Glows in dark	Does not glow in dark
12.	Burning in air	Forms P4O10	Forms P4O10
13.	Reaction with NaOH	Gives phosphine	No reaction
14.	Reaction with Cl2	Form PCl3 and PCl5 (spontaneously)	On heating forms PCl3 and PCl5
15.	Reaction with hot HNO3	Forms H3PO4	Forms H3PO4
16.	Stability	Unstable	Stable
17.	Conductivity	Bad conductor	Semiconductor
18.	Molecular formula	P4	Complex polymer

Uses of phosphorus: 
i) In match industry.  In match box.
side contains:  Red P or P₂S₃ + Sand + Glue.
On tip:  Red P + oxidizing agents like KClO₃ or KNO₃ or Pb₃O₄ + glass powder or chalk for friction.
ii) As rat poison i.e., yellow P₄.
iii)  In manufacture of fertilizers and alloys.
iv) In treatment of leukemia and other blood disorders ie., radioactive P³². 

Illustration 13: Why white phosphorous is more reactive than red phosphrous?
Solution: In white ‘P’ atoms are tetrahedrally distributed with a bond angle 60⁰ causing more strain to the molecule.  In addition to it P – P covalent bonds are weak with a bond dissociation energy of 48k cal/mole.  Red ‘P’ exists as polymerized P₄ tetrahedral units.

Compounds of phosphorus:
Phosphine (PH₃):
It was disocovered by Gengembre in 1783. 
Prep:
i) By heating white P with 30 – 40% NaOH solution in an inert atmosphere. (Lab method).

${\mathrm{P}}_4+3\mathrm{NaOH}+3{\mathrm{H}}_2\mathrm{O}⟶\underset{\text{Sodium hypophosphite})}{3{\mathrm{NaH}}_2{\mathrm{PO}}_2}+{\mathrm{PH}}_3$
ii) By the action of water or dil mineral acid on metallic phosphides:

$\begin{array}{l}{\mathrm{Na}}_3\mathrm{P}+3{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{PH}}_3+3\mathrm{NaOH}\\ \\ {\mathrm{Ca}}_3{\mathrm{P}}_2+{\mathrm{H}}_2\mathrm{O}⟶2{\mathrm{PH}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2\\ \\ 2\mathrm{AIP}+3{\mathrm{H}}_2{\mathrm{SO}}_4⟶2{\mathrm{PH}}_3+{\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\end{array}$
iii)  By heating phosphonium iodide with 30% KOH:

$\begin{array}{rl}& {\mathrm{PH}}_4\mathrm{I}+\mathrm{NaOH}⟶\underset{\text{(Pure phosphine)}}{{\mathrm{PH}}_3}+\mathrm{Nal}+{\mathrm{H}}_2\mathrm{O}\end{array}$
iv) By heating phosphorous acid (decomposition):

$\begin{array}{rl}& {4\mathrm{H}}_3{\mathrm{PO}}_3⟶\underset{\mathrm{Orthophosphoric} \mathrm{acid}}{3{\mathrm{H}}_3{\mathrm{PO}}_4}+{\mathrm{PH}}_3\end{array}$

Physical properties:  It is a colourless gas with the odour like rotten fish, highly poisonous slightly soluble in water.
Pure PH₃ is not inflammable.
It liquefies at – 89⁰C and solidifies at – 134⁰C.

Chemical properties:
i) Basic nature: It is neutral toward litmus.  However it is a weak base, even weaker than ammonia,  it reacts with HCl, HBr or HI to forms phosphonium compounds.

$$\begin{gathered} {\mathrm{PH}}_3+\mathrm{HCl}⟶\underset{(\mathrm{Phosphonium} \mathrm{chloride})}{{\mathrm{PH}}_4\mathrm{Cl}} \\ {\mathrm{PH}}_3+\mathrm{HBr}⟶\underset{(\mathrm{Phosphonium} \mathrm{bromide})}{{\mathrm{PH}}_4\mathrm{Br}} \\ {\mathrm{PH}}_3+\mathrm{HI}⟶\underset{(\mathrm{Phosphonium} \mathrm{iodide})}{{\mathrm{PH}}_4\mathrm{I}} \end{gathered}$$

ii) Decomposition:  $4{\mathrm{PH}}_3\underset{\text{or electric arc}}{\overset{{38}^{\circ }\mathrm{C}}{\to }}{\mathrm{P}}_4+6{\mathrm{H}}_2$

iii)  Combustibility:  Pure PH₃, is not spontaneously inflammable but ordinary PH₃ is spontaneously inflammable due to the pressure of P₂H₄.

$4{\mathrm{PH}}_3+8{\mathrm{O}}_2⟶{\mathrm{P}}_4{\mathrm{O}}_{10}+6{\mathrm{H}}_2\mathrm{O}$

iv) Reaction with metallic salts:

$\begin{array}{rl}& 3{\mathrm{CuSO}}_4+2{\mathrm{PH}}_3⟶\underset{\mathrm{Cupric} \mathrm{phosphide}(\mathrm{Black} \mathrm{ppt})}{{\mathrm{Cu}}_3{\mathrm{P}}_2}+3{\mathrm{H}}_2{\mathrm{SO}}_4\end{array}$

$\begin{array}{rl}& 3{\mathrm{AgNO}}_3+{\mathrm{PH}}_3⟶\underset{\text{silver phosphide(Blackppt)}}{{\mathrm{Ag}}_3\mathrm{P}}+3{\mathrm{HNO}}_3\end{array}$

v) Reaction with chlorine: PH₃ burn in the atmosphere of chlorine.

${\mathrm{PH}}_3+3{\mathrm{Cl}}_2⟶{\mathrm{PCl}}_5+3\mathrm{HCl}$

vi) Reaction with anhydrous AlCl₃ and SnCl₄.

$\begin{array}{l}{\mathrm{AlCl}}_3+2{\mathrm{PH}}_3⟶{\mathrm{AlCl}}_3\cdot 2{\mathrm{PH}}_3\mid \\ \\ {\mathrm{SnCl}}_4+2{\mathrm{PH}}_3⟶\underset{\left(\text{Addition compound}\right)}{{\mathrm{SnCl}}_4\cdot 2{\mathrm{PH}}_3}\end{array}$

Structure:  It has pyramidal structure like ammonia.

In PH₃ ∠HPH = 93⁰

In NH₃ ∠HNH = 107⁰

Uses of pH₃:
i) Holme signals: A mixture of CaC₂ and Ca₃P₂, on reaction with water gives phosphine which catches fire and lights up acetylene.  The burning gases serve the purpose of signals.  These are used in ships.
ii) Smoke screen: Calcium phosphide is used in making smoke screens.  PH₃ obtained from it catches fire to give needed smoke.
iii)  Rat poison:  Zinc phosphide is used as rat poison, which gives PH₃. 
iv) Cellphos: Cellphos is a trade name of AlP (aluminium phosphide) and used as fumigant. In presence of moisture, it gives pH₃, which kills insects and pests.

Orthophosphoric acid (H₃PO₄):
Prep:
i) By dissolving P₄O₁₀ in boiling water:

${\mathrm{P}}_4{\mathrm{O}}_{10}+6{\mathrm{H}}_2\mathrm{O}⟶4{\mathrm{H}}_3{\mathrm{PO}}_4$

ii) By the hydrolysis of PCl₅

${\mathrm{PCl}}_5+4{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{H}}_3{\mathrm{PO}}_4+5\mathrm{HCl}$

iii)  By heating red P with conc. HNO₃ in presence of iodine catalyst:

$\underset{\text{(red)}}{\mathrm{P}}+5{\mathrm{HNO}}_3⟶{\mathrm{H}}_3{\mathrm{PO}}_4+{\mathrm{H}}_2\mathrm{O}+5{\mathrm{NO}}_2$

iv) By heating calcium phosphate with 60% H₂SO₄:

${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2+3{\mathrm{H}}_2{\mathrm{SO}}_4⟶3{\mathrm{CaSO}}_4+2{\mathrm{H}}_3{\mathrm{PO}}_4$

Properties: 
i) It is a transparent deliquescent crystalline solid.
ii) It melts at 42.3⁰C
iii)   It absorb water and forms colourless syrupy mass.
iv) It is highly soluble in water. 
v) Heating effects:

 $2{\mathrm{H}}_3{\mathrm{PO}}_4\stackrel{{250}^{\circ }\mathrm{C}}{⟶}{\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_7+{\mathrm{H}}_2\mathrm{O}\stackrel{{316}^{\circ }\mathrm{c}}{⟶}2{\mathrm{HPO}}_3+{\mathrm{H}}_2\mathrm{O}$

${\mathrm{H}}_3{\mathrm{PO}}_4\underset{\text{hented}}{\overset{\mathrm{strongly}}{\to }}{\mathrm{P}}_4{\mathrm{O}}_{10}+6{\mathrm{H}}_2\mathrm{O}$
vi) Acidic nature: It is a tribasic acid and ionise in three steps

${\mathrm{H}}_3{\mathrm{PO}}_4\stackrel{\text{readily}}{⟶}{\mathrm{H}}^{+}+{\mathrm{H}}_2{\mathrm{PO}}_4^{-} \text{(primarysalt)}$

 ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}\stackrel{\text{weaky}}{⟶}{\mathrm{H}}^{+}+{\mathrm{HFO}}_4^{-}$(secondary salt)

 ${\mathrm{HPO}}_4^{--}\frac{\text{V.veak}}{\text{ionization}}{\mathrm{H}}^{+}+{\mathrm{PO}}_4^{--}$(normal or tertiary salt)

vii) Reaction with ammonium molybdate, in presence of nitric acid :  (test of ${\mathrm{PO}}_4^{3-}\text{ion}$

 $\begin{array}{c}{\mathrm{H}}_3{\mathrm{PO}}_4+21{\mathrm{HNO}}_3+12{\left({\mathrm{NH}}_4\right)}_2{\mathrm{M}}_0{\mathrm{O}}_4⟶\underset{\begin{array}{c}\text{Ammonium phosphom olybdate}\\ \left(\text{Canary yellow ppt}\right)\\ +2\mathbb{1}N{H}_4{\mathrm{NO}}_3+12{\mathrm{H}}_2\mathrm{O}\end{array}}{{\left({\mathrm{NH}}_4\right)}_3{\mathrm{PO}}_4\cdot 12{\mathrm{M}}_0{\mathrm{O}}_3}\end{array}$

Uses of H₃PO₄:
i) In medicine, as a substitute for H₂SO₄ in the preparation of C₂H₄ from C₂H₅OH, HBr from KBr and HI from NaI.
ii) As a flowering agent in soft drinks.
iii) In making fertilizers and other phosphates.
iv) For preparing metaphosphoric acid.
v) As a stabilizer for H₂O₂

Orthophosphorus acid (H₃PO₃):
Prep:
i) By dissolving phosphorus trioxide in water.

${\mathrm{P}}_4{\mathrm{O}}_6+6{\mathrm{H}}_2\mathrm{O}⟶4{\mathrm{H}}_3{\mathrm{PO}}_3$

ii) By hydrolysis of phosphorus trichloride

${\mathrm{PCl}}_3+3{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{H}}_3{\mathrm{PO}}_3+3\mathrm{HCl}$

Prop:
i) It is colourless crystalline compound (HP = 73⁰C)
ii) It is highly soluble in water.
iii)  Acidic nature:  It is a strong and dibasic acid.

$\begin{array}{l}{\mathrm{H}}_3{\mathrm{PO}}_3\to {\mathrm{H}}^{+}+\left({\mathrm{H}}_2{\mathrm{PO}}_3^{-}\right)\to {\mathrm{H}}^{+}+{\left({\mathrm{HPO}}_3\right)}^{2-}\\ \\ {\mathrm{K}}_1={10}^{-1};{\mathrm{K}}_2=2\times {10}^{-7}\end{array}$

It thus, forms two series of salts such as NaH₂PO₃ and Na₂HPO₃ known as primary phosphates and secondary phosphates respectively.
iv) Decomposition: (disproportionation reaction)
$4{\mathrm{H}}_3{\mathrm{PO}}_3⟶3{\mathrm{H}}_3{\mathrm{PO}}_4+{\mathrm{PH}}_3$

v) Reducing nature: It acts as a strong reducing agent the potential equation is

$\begin{array}{l}{\mathrm{H}}_3{\mathrm{PO}}_3+{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{H}}_3{\mathrm{PO}}_4+2\mathrm{H}\\ \\ \mathrm{e}.{\mathrm{g}}_{.. }{\mathrm{AgNO}}_3+\mathrm{H}⟶\mathrm{Ag}+{\mathrm{HNO}}_3\\ \\ {\mathrm{CuSO}}_4+2\mathrm{H}⟶\mathrm{Cu}+{\mathrm{H}}_2{\mathrm{SO}}_4\\ \\ 2{\mathrm{HgCl}}_2+2\mathrm{H}⟶{\mathrm{Hg}}_2{\mathrm{Cl}}_2+2\mathrm{HCl}\\ \\ {\mathrm{I}}_2+2\mathrm{H}⟶2\mathrm{Hl}\\ \\ {\mathrm{SO}}_2+4\mathrm{H}⟶\mathrm{S}+2{\mathrm{H}}_2\mathrm{O}\end{array}$

Uses:  As reducing agent.

Illustration 14:  H₃PO₃ is diprotic acid.  Explain.
Solution:   H₃PO₃ has three H-atoms and therefore, it is expected to be tribasic.  However, in its structure, two hydrogen atoms are joined through oxygen atoms and are ionisable.  The third H-atom is linked to P and is non-ionisable.

${\mathrm{H}}_3{\mathrm{PO}}_3\to {\mathrm{HPO}}_3^{2-}+2{\mathrm{H}}^{+}$

Fertilizers:  These are chemical compounds prepared by artificial means which supply the three most essential elements – N, P and K to the soil.
Types of fertilizers:
Depending upon the nourishing elements N, P and K they are divided into
I) Nitrogenous fertilizers: These provides nitrogen to the plants.  They are

$\begin{array}{l}2{\mathrm{NH}}_3+{\mathrm{CO}}_2\stackrel{200\mathrm{atm}}{⟶}+\underset{\text{Ammonium carbamate}}{{\mathrm{H}}_2{\mathrm{NCOONH}}_4}\\ \\ {\mathrm{H}}_2{\mathrm{NCOONH}}_4⟶\underset{\mathrm{urea}}{{\mathrm{NH}}_2{\mathrm{NH}}_2}+{\mathrm{H}}_2\mathrm{O}\end{array}$
a) Urea (NH₂CONH₂):
It is highly soluble in water and hence requires air tight packing. It does not alter the pH of the soil.
b) Ammonium sulphate (Sindrifertilizer):
Prep:

$\begin{array}{l}{\mathrm{NH}}_3+{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{NH}}_4\mathrm{OH}\\ \\ 2{\mathrm{NH}}_4\mathrm{OH}+{\mathrm{CO}}_2⟶{\left({\mathrm{NH}}_4\right)}_2{\mathrm{CO}}_3+{\mathrm{H}}_2\mathrm{O}\\ \\ {\left({\mathrm{NH}}_4\right)}_2{\mathrm{CO}}_3+\underset{\left(G\mathrm{y}p\mathrm{sum}\right)}{{\mathrm{CaSO}}_4}⟶{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4+\underset{\left(\text{Insoluble}\right)}{{\mathrm{CaCO}}_3}\downarrow \end{array}$

c) Basic calcium nitrate (nitrate of lime or Norwegian salt petre) (Ca(NO₃)₂.CaO):
Prep:   

$$\begin{gathered} \underset{\text{(Iime }\mathrm{Stone}) \\ }{{\mathrm{CaCO}}_3}+2{\mathrm{HNO}}_3⟶\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2 \\ \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+\underset{\text{(lime)}}{\mathrm{CaO}}⟶\underset{\text{(Basic calcium nitrate})}{\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2\mathrm{CaO}} \end{gathered}$$

Being highly deliquescent, it is packed in water proof bags.

d) Calcium cyanamide (CaCN₂):
Prep:   ${\mathrm{CaC}}_2+{\mathrm{N}}_2⟶\underset{\text{Nitrolim}}{\underbrace{\underset{\text{calcium cyanamide}}{{\mathrm{CaCN}}_2+C}}}$

Prop:  In soil, it is converted into urea which then decomposes into ammonia.  Ammonia is finally converted into nitrates by nitrifying bacteria.

${\mathrm{CaCN}}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2⟶\underset{\left(\mathrm{C}\text{yanamide}\right)}{\mathrm{CN}{\mathrm{NH}}_2}+{\mathrm{CaCO}}_3$

$\begin{array}{l}{\mathrm{CNNH}}_2+{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{NH}}_2{\mathrm{CONH}}_2 \left(\text{urea}\right)\\ \\ {\mathrm{NH}}_2{\mathrm{CONH}}_2+{\mathrm{H}}_2\mathrm{O}⟶2{\mathrm{NH}}_3+{\mathrm{CO}}_2\end{array}$

It is added to the soil before sowing and not when the plants are actually growing.
e) Calcium ammonium nitrate Ca (NO₃)₂. NH₄NO₃. CAN is known as Nangal fertilizer.
Prep: 

$$\begin{gathered} \underset{\text{(Haber’s process)}}{{\mathrm{NH}}_3}+{\mathrm{HNO}}_3⟶\underset{\text{(explosive)}}{{\mathrm{NH}}_4{\mathrm{NO}}_3} \\ \underset{\text{(Powdered lime stone)}}{{\mathrm{CaCO}}_3}+2{\mathrm{HNO}}_3⟶\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2 \\ \begin{array}{rl}& \mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+{\mathrm{NH}}_4{\mathrm{NO}}_3⟶\underset{\text{(does not explode)}}{\underset{CAN}{\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2\cdot {\mathrm{NH}}_4{\mathrm{NO}}_3}}\end{array} \end{gathered}$$

Prop:  It is hygroscopic; therefore, the pellets are coated with calcium silicates as to protect from moisture.
It is more soluble in water and does not make the soil acidic and therefore, is superior to ammonium sulphate.
Phosphatic fertilizers:
These provides phosphorus to the plants.
a) Superphosphate of lime or calcium superphosphate:
Prep:

${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2+\underset{70\%}{2{\mathrm{H}}_2{\mathrm{SO}}_4}+4{\mathrm{H}}_2\mathrm{O}⟶\underset{\text{Super phosphate of lime}}{\underbrace{\mathrm{Ca}{\left({\mathrm{H}}_2{\mathrm{PO}}_4\right)}_2+2{\mathrm{CaSO}}_4}}\cdot 2{\mathrm{H}}_2\mathrm{O}+\text{heat}$

Prop:  It is a fine powder and has 16 – 20% of P₂O₅.
b) Phosphatic slag or Thomas slag:
It is a by product of steel industry.
Prep: 

$\begin{array}{l}4\mathrm{P}+5{\mathrm{O}}_2⟶{\mathrm{P}}_4{\mathrm{O}}_{10}\\ \\ 6\mathrm{CaO}+{\mathrm{P}}_4{\mathrm{O}}_{10}⟶2{\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2 \left(\text{slag}\right)\end{array}$
Prop:  Fine powder is used as fertilizer.  It has 14 – 18% of P₂O₅.
c) Triple phosphate or Triple super phosphate:
This is another form of superphosphate.

Prep:   ${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2+\underset{\text{orthophosphoric acid}}{4{\mathrm{H}}_3{\mathrm{PO}}_4}⟶\underset{\text{Triple phosphate}}{3\mathrm{Ca}{\left({\mathrm{H}}_2{\mathrm{PO}}_4\right)}_2}$

Prop:    It has about three times the amount of available P₂O₅ in comparison to superphosphate of lime (i.e., 42 – 46% of P₂O₅) and hence called triple super phosphate.
d) Nitrophosphate or Nitrophos:
It is also known as calcium superphosphate nitrate.

Prep: ${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2+{\mathrm{HNO}}_3⟶\underset{\text{Nitrophosphate}}{\underbrace{\mathrm{Ca}{\left({\mathrm{H}}_2{\mathrm{PO}}_4\right)}_2+2\mathrm{Ca}\left({\mathrm{NO}}_3\right)}}$

Prop: This is a mixed fertilizer.  The advantage of this fertilizer is that in addition to phosphorous, it contains nitrogen as well.
III. Potash fertilizers: 
These provide potassium to plants.  e.g., KCl, KNO₃, K₂SO₄ are used as potash fertilizers.
N, P, K, Fertilizers:
Fertilizers containing N, P, K in suitable adjusted proportions are known as N, P, K fertilizers.
These are mixed fertilizers and are obtained by mixing nitrogenous, phosphatic and potash fertilizers in suitable proportions.
Ex:  Expression live 4 – 8 – 2 used for a mixed fertilizer indicates that it contains 4% N₂, 8% P₂O₅ and 2% K₂O.

Illustration 15: Write the composition of ‘superphosphate’ of lime, is it variable?
Solution: Mixture of calcium hydrogen phosphate and gypsum is known as super-phosphate of lime $\left[\mathrm{Ca}{\left({\mathrm{H}}_2{\mathrm{PO}}_4\right)}_2+2{\mathrm{CaSO}}_{4}2{\mathrm{H}}_2\mathrm{O}\right]$.  Composition of superphosphate is variable.

FORMULAE AND CONCEPTS AT A GLANCE

1. Nitrogen and phosphorus show both positive and negative oxidation states but the heavier elements show only positive oxidation states. Nitrogen show all the oxidation states from – 3 to + 5.

2. Nitrogen and phosphorus behave as non-metals, arsenic and antimony as metalloids and bismuth as a metal.

3. The reactivity of various allotropic forms of phosphorus, towards other substances, follows the following order White > Red > Black.

4. The basic nature, bond angle, thermal stability and dipole moments of hydrides (MH₃) decreases in the following order.
${\mathrm{NH}}_3>{\mathrm{PH}}_3>{\mathrm{AsH}}_3>{\mathrm{SbH}}_3>{\mathrm{BiH}}_3$

5. The reducing power, poisonous nature and covalent nature of hydrides increase in the following order.
${\mathrm{NH}}_3<{\mathrm{PH}}_3<{\mathrm{AsH}}_3<{\mathrm{SbH}}_3<{\mathrm{BiH}}_3$

6. The correct order of M.P. of hydrides is
${\mathrm{NH}}_3>{\mathrm{SbH}}_3>{\mathrm{AsH}}_3>{\mathrm{PH}}_3$

7. The correct order of B.P. of hydrides is
${\mathrm{PH}}_3<{\mathrm{AsH}}_3<{\mathrm{NH}}_3<{\mathrm{SbH}}_3$

8. Stability of trihalides of N – decreases in the following order
${\mathrm{NF}}_3>{\mathrm{NCl}}_3>{\mathrm{NBr}}_3$

9. Lewis base strength of trihalides of N – increases as follows.
${\mathrm{NF}}_3<{\mathrm{NCl}}_3<{\mathrm{NBr}}_3<{\mathrm{NI}}_3$

10. The ease of hydrolysis of trihalides of group 15 elements decreases as follows.
${\mathrm{NCl}}_3>{\mathrm{PCl}}_3>{\mathrm{AsCl}}_3>{\mathrm{SbCl}}_3>{\mathrm{BiCl}}_3$
${\mathrm{NF}}_3 \text{and }{\mathrm{PF}}_3$ donot hydrolysed.

11. Trihalides of P, As and Sb also behave as lewis acids and the acidic strength decreases down the group.
${\mathrm{PCl}}_3>{\mathrm{AsCl}}_3>{\mathrm{SbCl}}_3$

12. In case of trihalides of phosphorus lewis acid strength decreases from F → I.
${\mathrm{PF}}_3>{\mathrm{PCl}}_3>{\mathrm{PBr}}_3>{\mathrm{PI}}_3$
and the bond angle increases as the electronegativity of the halogen decreases from F→ I.
${\mathrm{PF}}_3<{\mathrm{PCl}}_3<{\mathrm{PBr}}_3<{\mathrm{PI}}_3$

13. In solid state PCl₅ exist as [PCl₄]⁺ [PCl₆]^– having tetrahedral and octahedral structures respectively; PBr₅ exists in solid as [PBr₄]⁺ [Br]^– while PI₅ exists as [PI₄]⁺ [I^–] in solution.

14. The normal oxides and hydroxides of nitrogen and phosphorus are strongly acidic; arsenic is weakly acidic, antimony is amphoteric and bismuth is largely basic.

15. The acidic strength of oxides of nitrogen increases in the order:
${\mathrm{N}}_2\mathrm{O}<\mathrm{NO}<{\mathrm{N}}_2{\mathrm{O}}_3<{\mathrm{N}}_2{\mathrm{O}}_4<{\mathrm{N}}_2{\mathrm{O}}_5$

16. The acidic strength of trioxides decreases in the following order
${\mathrm{N}}_2{\mathrm{O}}_3>{\mathrm{P}}_2{\mathrm{O}}_3>{\mathrm{As}}_2{\mathrm{O}}_3$

17. The acidic strength of pentaoxides decreases in the following order
${\mathrm{N}}_2{\mathrm{O}}_5>{\mathrm{P}}_2{\mathrm{O}}_5>{\mathrm{As}}_2{\mathrm{O}}_5>{\mathrm{Sb}}_2{\mathrm{O}}_5>{\mathrm{Bi}}_2{\mathrm{O}}_5$

18. The stability of pentaoxides decreases in the following order
${\mathrm{P}}_2{\mathrm{O}}_5>{\mathrm{As}}_2{\mathrm{O}}_5>{\mathrm{Sb}}_2{\mathrm{O}}_5>{\mathrm{N}}_2{\mathrm{O}}_5>{\mathrm{Bi}}_2{\mathrm{O}}_5$

19. All oxides of P, As and Sb are dimeric. Thus, trioxides and pentaoxides written as M₄O₆ and M₄O₁₀ respectively.

20. The strength and solubility of oxyacids of group 15 elements decreases rapidly in the following order.
${\mathrm{HNO}}_3>{\mathrm{H}}_3{\mathrm{PO}}_4>{\mathrm{H}}_3{\mathrm{AsO}}_4>{\mathrm{H}}_3{\mathrm{SbO}}_4$

21. BiOCl is called pearl white.

22. In tooth past, CaHPO₄.2H₂O is added as mild abrasive and polishing agent.

23. Arsenic trioxide (As₄O₆) is called white arsenic and is a poison.

24. Phosphorus pentaoxide (P₂O₁₀) due to its appearance as a snowy powder is called flowers of phosphorus.

25. SbF₃ is called swarts reagent, which is used as a fluorinating agent for various compounds of nonmetals.

26. Phosphine in combination with acetylene is used in preparing Holme’s signals for ship to know about the position of rocks or icebergs in the sea. Titanic sank in seawater on hitting the iceberg.
A mixture of CaC₂ and Ca₃P₂ is taken in a vessel which is allowed to be in contact with water.  Phosphine and acetylene are formed phosphine catches fire in air and lights up acetylene which acts as a signal for the approaching ship.
$\begin{array}{l}{\mathrm{CaC}}_2+2{\mathrm{H}}_2\mathrm{O}⟶\underset{\text{acetylene}}{\mathrm{CH}\equiv \mathrm{CH}}+\mathrm{Ca}(\mathrm{OH}{)}_2\\ \\ {\mathrm{Ca}}_3{\mathrm{P}}_2+6{\mathrm{H}}_2\mathrm{O}⟶\underset{\text{phosphine}}{3{\mathrm{PH}}_3}+3\mathrm{Ca}(\mathrm{OH}{)}_2\end{array}$

27. For drying of NH₃ quicklime (CaO) is used. Other dehydrating agents like H₂SO₄, CaCl₃, and P₂O₅ can not be used as they react with NH₃.

SOLVED PROBLEMS-1

Prob 1. Explain, molecular nitrogen N₂ is not particularly reactive.

Sol: In molecular nitrogen, there is a triple bond between two nitrogen atoms (N º N) and it is non-polar in character.  Due to the presence of a triple bond, it has very high bond dissociation energy (945 kJ mol^–1) and therefore it does not react with other elements under normal conditions and is very unreactive.  However it may react at higher temperature.  

Prob 2. NH₃ acts as a ligand but NH₄⁺ does not.  Explain.

Sol: Ammonia molecule  has a lone pair of electrons on the N-atom which it can donate to an electron acceptor.  Therefore, it can act as a ligand.  But, in NH₄⁺, the lone pair of electrons on N-atom has already been donated to the proton and hence, is not available for donation to an electron acceptor.  Hence, NH₄⁺ ion can not act as a ligand.

Prob 3. NH₃ is a strong base but NF₃ does not show any basic property.  Explain.

Sol: NF₃ has a pyramidal shape with one lone pair on N-atom.  The lone pair on N is in opposite direction to the N-F bond moments and therefore it has very low dipolemoment (about 0.234D). Thus it does not show donor properties.  But ammonia has high dipolemoment because its lone pair is in the same direction as the N – H bond moments.  Thus, NH₃ has donor properties.

Prob 4. NF₃ is an exothermic compound (DH_f = – 109 kJ/mol), whereas NCl₃ is an endothermic compound (DH_f = + 230 kJ/mol) explain.

Sol: NF₃ is an exothermic compound, whereas NCl₃ is an endothermic compound because in case of NF₃, N – F bond strength is greater than the F – F bond strength while in case of NCl₃, ‘Cl – Cl’ bond strength is greater than N – Cl bond strength.

Prob 5. The first ionization energy of ‘NO’ is less than that of N₂.  Explain.

Sol: In N₂, there is no unpaired electron in the molecular orbital.  So its first ionization energy is high.  But in NO, there is one unpaired electron in one of the p^* antibonding orbital.  Thus, this electron p* antibonding orbital is easily lost to give the nitrosonioum ion, NO⁺.  Hence, first ionization energy of NO is less than that of N₂.

Prob 6. Concentrated HNO₃ turns yellow on exposure to sunlight.  Why?

Sol: On exposure to sun light, HNO₃ decomposes into NO₂, O₂ and H₂O.  The presence of NO₂ in the partially decomposed HNO₃ gives it yellow colour.

Prob 7. Phosphoric acid has high viscosity and high melting point.  Why?

Sol: Phosphoric acid (H₃PO₄) has a tendency to form hydrogen bonding in concentrated solutions.  Therefore, it has high viscosity and is a syrupy liquid and has high boiling point.

Prob 8. Give one example each of oxyacid of P having the oxidation state (i) + 4   (ii)  + 3.

Sol: i)  Hypophosphoric acid (H₄P₂O₆)         ii)  Phosphorous acid (H₃PO₃)

Prob 9. Nitric oxide becomes brown when released in air.  Why?

Sol: When nitric oxide (NO) is released in air, it becomes brown due to the formation of NO₂ (nitrogen dioxide), which is a brown gas.

Reaction :  $\underset{\left(\mathrm{g}\right)}{2\mathrm{NO}}+{\mathrm{O}}_2\left(\mathrm{g}\right)⟶\underset{\left(\mathrm{Brown}\right)}{2{\mathrm{NO}}_2\left(\mathrm{g}\right)}$

Prob 10. Nitrous oxide (NO) supports combustion more vigorously than air.  Explain.

Sol:  Nitrous oxide decomposes above 550⁰C yielding oxygen and nitrogen i.e., $2{\mathrm{N}}_2\mathrm{O}\to 2{\mathrm{N}}_2+{\mathrm{O}}_2$.  Because one third of the gas liberated is oxygen, N₂O supports combustion better than air.

SOLVED PROBLEMS-2

Prob 1. The compound which exists as a molecule in gas phase but ionic in solid state is

(A)  PCl₅               (B)  PCl₃               (C)  PCl₅               (D)  CCl₄

Sol: (A) PCl₃, exists in nature in gas phase but ionic in solid state, x-ray studies have shown that PCl₅ exists as ${\left[{\mathrm{PCl}}_4\right]}^{+}{\left[{\mathrm{PCl}}_5\right]}^{-}$ in the crystalline state.

Prob 2. In diammonium phosphate (NH₄)₂HPO₄, the percentage of P₂O₅ is

(A)  35.27               (B)  46.44               (C)  51.99               (D)  53.78

Sol: (D)

  $\underset{2 \mathrm{mole}}{2{\left({\mathrm{NH}}_4\right)}_2 {\mathrm{HPO}}_4} \to \underset{1 \mathrm{mole}}{{\mathrm{P}}_2{\mathrm{O}}_5}$

    2 $\times$ 132 = 264g        142g

$\therefore \mathrm{\%}\text{ of }{\mathrm{P}}_2{\mathrm{O}}_5=\frac{142}{264}\times 100=53.78$

Prob 3. The ammonium compound which on heating does not give ammonia is

(A)  NH₄Cl               (B)  NH₄NO₂               (C)  (NH₄)₂SO₄               (D)  (NH₄)₂CO₃

Sol: (B) NH₄ NO₂ gives N₂ and H₂O instead of NH₃

${\mathrm{NH}}_4{\mathrm{NO}}_2\stackrel{∆}{\to }{\mathrm{N}}_2+2{\mathrm{H}}_2\mathrm{O}$

Prob 4. A colourless gas was slowly passed over heated copper.  It gave rise to an equal volume of another colourless gas which was odourless, non combustible and a non supporter of combustion, the original gas was

(A)  nitric oxide
(B)  ammonia
(C)  hydrogen chloride
(D)  nitrous oxide

Sol: (D) ${\mathrm{N}}_2\mathrm{O}+\mathrm{Cu}⟶\mathrm{CuO}+{\mathrm{N}}_2$

Prob 5. The well known chemical fertilizer nitrolim is made by passing nitrogen over heated

(A)  limestone               (B)  quick lime               (C)  calcium carbide               (D)  gypsum

Sol: (C)  ${\mathrm{CaC}}_2+{\mathrm{N}}_2⟶{\mathrm{CaCN}}_2+\mathrm{C}$

Prob 6. Ammonium carbonate is a smelling salt because

(A)  it has pleasant smell
(B)  it decomposes
(C)  it is crystalline
(D)  it gives the smell of ammonia

Sol: (D) (NH₄)₂CO₃ is a smelling salt because it gives the smell of ammonia.

Prob 7. When equal weights of the two fertilizers urea and ammonium sulphate are taken, urea contains

(A)  less nitrogen than ammonium sulphate     

(B)  as much nitrogen as ammonium sulphate

(C)  twice the amount of nitrogen present in ammonium sulphate

(D)  more than twice the amount of nitrogen present in ammonium sulphate

Sol: (D)

% of N in urea = $\frac{28}{60}\times 100=46.66$

% of N in ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4 = \frac{28}{132}\times 100=21.2$

Prob 8. When HNO₃ is dropped into the palm and washed with water it turns into yellow.  It shows the presence of

(A)  NO₂               (B)  N₂O               (C)  NO               (D)  N₂O₃

Sol: (A) Nitric acid usually acquires yellow colour due to its decomposition by sunlight into NO₂.

$4{\mathrm{HNO}}_3\stackrel{\mathrm{sunlight} }{\to }4{\mathrm{NO}}_2+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$

The yellow colour of the acid can be removed by warming it to 60 – 80⁰C and bubbling dry air through it.

Prob 9. Fixation of nitrogen means

(A)  reaction of nitrogen with oxygen               

(B)  conversion of free atmospheric nitrogen into nitrogen compounds

(C)  decomposition of nitrogenous compounds to yield free nitrogen

(D)  the action of denitrifying bacteria on nitrogen compounds

Sol: (B) conversion of free atmospheric nitrogen into nitrogen compounds

Prob 10. Which of the following properties is not correct regarding red phosphorus?

(A)  Soluble in CS₂                                         

(B)  Does not undergo oxidation at room temperature

(C)  Does not react with NaOH solution

(D)  Non-poisonous

Sol: (A) Soluble in CS₂