Liquid nitrogen

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Liquid nitrogen
Lecture 14
VA group. Nitrogen and Phosphorous and their
compounds.
PhD Halina Falfushynska
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Atomic and Physical Properties of Group 15
Elements
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Electronic Configuration. The valence shell
electronic configuration of these elements is
ns2np3. The s orbital in these elements is
completely filled and p orbitals are half-filled,
making their electronic configuration extra
stable. Atomic and Ionic Radii. Covalent and
ionic (in a particular state) radii increase in
size down the group. There is a considerable
increase in covalent radius from N to P. However,
from As to Bi only a small increase in covalent
radius is observed. This is due to the presence
of completely filled d and/or f orbitals in
heavier members. Ionisation Enthalpy. Ionisation
enthalpy decreases down the group due to gradual
increase in atomic size. Because of the extra
stable half-filled p orbitals electronic
configuration and smaller size, the ionisation
enthalpy of the group 15 elements is much greater
than that of group 14 elements in the
corresponding periods. The order of successive
ionisation enthalpies, as expected is ?H1 lt ?H2
lt ?H3 Physical Properties. All the elements of
this group are polyatomic. Dinitrogen is a
diatomic gas while all others are solids.
Metallic character increases down the group.
Nitrogen and phosphorus are non-metals, arsenic
and antimony metalloids and bismuth is a metal.
This is due to decrease in ionisation enthalpy
and increase in atomic size. The boiling points,
in general, increase from top to bottom in the
group but the melting point increases up to
arsenic and then decreases up to bismuth. Except
nitrogen, all the elements show allotropy.
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Preparation of dinitrogen

• In the laboratory, dinitrogen is prepared by
  treating an aqueous solution of ammonium chloride
  with sodium nitrite.
• NH4CI(aq) NaNO2 (aq) ? N2 (g) 2H2O(l) NaCl
  (aq)
• It can be obtained by the thermal decomposition
  of ammonium dichromate.
• (NH4)2Cr2O7 (Heat) ???? N2 4H2O Cr2O3
• Very pure nitrogen can be obtained by the thermal
  decomposition of sodium or barium azide.
• Ba(N3)2 ? Ba 3N2
• Air (4N2 O2) C ? 4N2 CO2
• NH3 3O2 ? 2N2 6H2O
• 2NH3 3Cl2 ? N2 6HCl

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Reactivity towards hydrogen
Reactivity towards oxygen
All the elements of Group 15 form hydrides of the
type EH3 where E N, P, As, Sb or Bi. N2(g)
3H2(g) (773 k) gt 2NH3(g) ?H 46.1 kJmol1 ?4
6?2 (heat, p) gt 4??3 The stability of
hydrides decreases from NH3 to BiH3 . the
reducing character of the hydrides increases.
Ammonia is only a mild reducing agent while BiH3
is the strongest reducing agent amongst all the
hydrides. Basicity also decreases in the order
NH3 gt PH3 gt AsH3 gt SbH3 gt BiH3.
All these elements form two types of oxides E2O3
and E2O5. The oxide in the higher oxidation state
of the element is more acidic than that of lower
oxidation state. Their acidic character decreases
down the group. The oxides of the type E2O3 of
nitrogen and phosphorus are purely acidic. N2
(g) O2 (g) (heat) gt 2NO (g) P4 5O2 (heat)
gt 2P4O10
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Reactivity towards halogens
Reactivity towards metals
All these elements react with metals to form
their binary compounds exhibiting 3 oxidation
state, such as, Ca3N2 (calcium nitride) Ca3P2
(calcium phosphide), Na3As2 (sodium arsenide),
Zn3Sb2 (zinc antimonide) and Mg3Bi2 (magnesium
bismuthide). 3Mg N2 gt Mg3N2 Mg3N2 6H2O gt
3Mg(OH)2 2NH3
These elements react to form two series of
halides EX3 and EX5. Nitrogen does not form
pentahalide. Pentahalides are more covalent than
trihalides. All the trihalides of these elements
except those of nitrogen are stable. In case of
nitrogen, only NF3 is known to be stable. P4
6Cl2 gt 4PCl3 3PCl5 2P gt 5PCl3 3PCl5 P2O5
gt 5POCl3
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Ammonia

• Ammonia is present in small quantities in air and
  soil where it is formed by the decay of
  nitrogenous organic matter e.g., urea.
• NH2CONH2 2H2O ? (NH4)2CO3 ? 2NH3 H2O CO2
• On a small scale ammonia is obtained from
  ammonium salts which decompose when treated with
  caustic soda or lime.
• 2NH4Cl Ca(OH)2 ? 2NH3 2H2O CaCl2
• (NH4)2 SO4 2NaOH ? 2NH3 2H2O Na2SO4
• On a large scale, ammonia is manufactured by
  Habers process.
• N2(g) 3H2(g) ? 2NH3(g) ?H 46.1 kJ mol-1

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Flow chart for the manufacture of ammonia
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Phosphine

• Phosphine is prepared by the reaction of calcium
  phosphide with water or dilute HCl.
• Ca3P2 6H2O ? 3Ca(OH)2 2PH3
• Ca3P2 6HCl ? 3CaCl2 2PH3
• In the laboratory, it is prepared by heating
  white phosphorus with concentrated NaOH solution
  in an inert atmosphere of CO2.
• ?4 3??? 3?2? ? ??3 3??2??4
• PH4I (phosphonium iodide)KOH?KI H2OPH3

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Properties of Ammonia

• Ammonia gas is highly soluble in water. Its
  aqueous solution is weakly basic due to the
  formation of OH ions.
• NH3(g) H2O(l) ? NH4 (aq) OH (aq)
• 3CuO 2NH3 ? 3Cu 3H2O N2
• It forms ammonium salts with acids, e.g., NH4Cl,
  (NH4)2SO4, etc. As a weak base, it precipitates
  the hydroxides of many metals from their salt
  solutions.
• 2FeCl33NH4OH?Fe2O3xH2O (brown ppt) 3NH4Cl
• The ammonia molecule can act is a Lewis base
• Cu2 (aq, blue) 4 NH3(aq, deep blue) ?
  Cu(NH3)42(aq)
• Ag (aq, colourless) Cl- ? AgCl (s, white ppt)
• AgCl (s, white ppt)2NH3 (aq) ?Ag(NH3)2Cl)(aq,co
  lourless)

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Properties of Ammonia
Preparation of Potassium Amide. Potassium amide
is prepared by dissolution of potassium in liquid
ammonia.
Ammonia Fountain. Demonstration of the high
solubility of gaseous ammonia in water
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Nitrogen oxides
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(No Transcript)
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Nitric acid

• In the laboratory, nitric acid is prepared by
  heating KNO3 or NaNO3 and concentrated H2SO4 in a
  glass retort NaNO3 H2SO4 ? NaHSO4 HNO3

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Preparation of Nitric acid
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Nitric acid

• In aqueous solution, nitric acid behaves as a
  strong acid giving hydronium and nitrate ions.
• HNO3(aq) H2O(l) ? H3O (aq) NO3 (aq)
• Concentrated nitric acid is a strong oxidising
  agent and attacks most metals except noble metals
  such as gold and platinum.
• 8HNO3 (dilute) 3Cu ? 3Cu(NO3)2 2NO 4H2O
• 4Sn 10HNO3 ? 4Sn(NO3)2 NH4NO3 3H2O

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• Some metals (e.g., Cr, Al) do not dissolve in
  concentrated nitric acid because of the formation
  of a passive film of oxide on the surface.
• Concentrated HNO3 also oxidises nonmetals and
  their compounds. Iodine is oxidised to iodic
  acid, carbon to carbon dioxide, sulphur to H2SO4,
  and phosphorus to phosphoric acid.
• I2 10HNO3 ? 2HIO3 10 NO2 4H2O
• C 4HNO3 ? CO2 2H2O 4NO2
• S8 48HNO3(conc.) ? 8H2SO4 48NO2 16H2O
• P4 20HNO3(conc.) ? 4H3PO4 20 NO2 4H2O

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Brown Ring Test

• The familiar brown ring test for nitrates depends
  on the ability of Fe2 to reduce nitrates to
  nitric oxide, which reacts with Fe2 to form a
  brown coloured complex.

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Devarda's test

• Devarda's alloy (Cu/Al/Zn) is a reducing agent.
  When reacted with nitrate in sodium hydroxide
  solution, ammonia is liberated.
• 3 NO-3 8 Al 5 OH- 18 H2O ? 3 NH3 8
  Al(OH)4-
• Aluminium is the reductant in this reaction.

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Test for Ammonia
Test for Ammonia using Nessler's Agent. Ammonia
is tested in a 110 dilution row using K2HgI4.
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Phosphorus. Allotropic Forms

• White phosphorus is a translucent white waxy
  solid. It is poisonous, insoluble in water but
  soluble in carbon disulphide and has
  chemiluminescence.
• ?4 3NaOH 3H2O ? PH3 NaH2PO2
• ?4 3?2 ? 2?2?3
• ?2?3 ?2 ? ?2?5
• 3Mg 1/2P4 ? Mg3P2
• 2P 3Cl2 ? 2PCl3

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White phosphorus
White phosphorus exposed to air glows in the
darkness
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Red phosphorus

• It is obtained by heating white phosphorus at
  573K in an inert atmosphere for several days.
  When red phosphorus is heated under high
  pressure, a series of phases of black phosphorus
  are formed.
• Red phosphorus possesses iron grey lustre. It is
  odourless, non-poisonous and insoluble in water
  as well as in carbon disulphide.
• Chemically, red phosphorus is much less reactive
  than white phosphorus. It does not glow in the
  dark.

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Black phosphorus

• It has two forms a-black phosphorus and ß-black
  phosphorus.
• a-Black phosphorus is formed when red phosphorus
  is heated in a sealed tube at 803K. It can be
  sublimed in air and has opaque monoclinic or
  rhombohedral crystals. It does not oxidise in
  air.
• ß-Black phosphorus is prepared by heating white
  phosphorus at 473 K under high pressure. It does
  not burn in air up to 673 K.

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Phosphorus Tri- and Pentachlorides

• They are obtained by the action of thionyl
  chloride with white phosphorus.
• P4 8SOCl2 ? 4PCl3 4SO2 2S2Cl2
• P4 10SOCl2 ? 4PCl5 10SO2

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Reaction of Phosphorus Halides
PCl3 3H2O ? H3PO3 3HCl PCl5 H2O ? POCl3
2HCl POCl3 3H2O ? H3PO4 3HCl CH3COOH PCl5
? POCl3 HCl CH3COCl H2SO4 PCl5 ? POCl3
HCl SO2(OH)Cl POCl3 3H2O ? H3PO4 3HCl POCl3
3ROH ? PO(OH)3 3RCl 2Ag PCl5 ? 2AgCl
PCl3 Sn 2PCl5 ? SnCl4 2PCl3
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Oxoacids of Phosphorus
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Properties of phosphorus oxoacids and their salts

• The acids which contain PH bond have strong
  reducing properties.
• 4 AgNO3 2H2O H3PO2 ? 4Ag 4HNO3 H3PO4
• Acids in 3 oxidation state of phosphorus tend to
  disproportionate to higher and lower oxidation
  states. 4H3PO3 ? 3H3PO4 PH3
• 3H(PH2O2) 2HNO3 ? 3H2(PHO3) 2NO? H2O
• 5H4P2O6 3H2SO4 2KMnO4 2H2O ? 10H3PO4
  2MnSO4 K2SO4
• Salts of phosphorus oxoacids hydrolyze and base
  or neutral medium occurs

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Applications of nitrogen compounds

• As a modified atmosphere, pure or mixed with
  carbon dioxide, to preserve the freshness of
  packaged or bulk foods
• Nitrogen can be used instead of CO2 to pressurize
  kegs of some beers, in particular, stouts and
  British ales, due to the smaller bubbles it
  produces, which make the dispensed beer smoother
  and headier
• Liquid nitrogen is used in the cryopreservation
  of blood, reproductive cells (sperm and egg), and
  other biological samples. It is used in the
  clinical setting in cryotherapy to remove cysts
  and warts on the skin.

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Applications of nitrogen compounds

• Nitrous oxide (N2O), "laughing gas, was
  discovered early in the 19th century to be a
  partial anesthetic, though it was not used as a
  surgical anesthetic until later.
• Nitrogen-containing drugs are drugs derived from
  plant alkaloids, such as morphine (there exist
  many alkaloids known to have pharmacological
  effects in some cases, they appear natural
  chemical defenses of plants against predation).
  Drugs that contain nitrogen include all major
  classes of antibiotics and organic nitrate drugs
  like nitroglycerin and nitroprusside that
  regulate blood pressure and heart action by
  mimicking the action of nitric oxide.

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Applications of phosphorous compounds

• White phosphorus, called "WP" (slang term "Willie
  Peter") is used in military applications as
  incendiary bombs, for smoke-screening as smoke
  pots and smoke bombs, and in tracer ammunition.
• The spontaneous combustion of phosphine is
  technically used in Holmes signals. Containers
  containing calcium carbide and calcium phosphide
  are pierced and thrown in the sea when the gases
  evolved burn and serve as a signal.
• Phosphine is also used in smoke screens.