Chemistry of hydrogen and its advancements.

Chemistry of
Hydrogen (1H)
• The first element of the periodic
table.
• Atomic Number = 1
• Atomic weight = 1.0079
• Electronic configuration = 1s1

Isotopes of
Hydrogen
1. Protium / Hydrogen
2. Deuterium
3. Tritium

Isotopes of Hydrogen
1) Protium / Hydrogen (H)
 It is the most commonly available isotope.
 It constitutes 99% of total hydrogen available in
nature.
 The molecule of ordinary hydrogen is diatomic (H2)
 The nucleus of atom consist of single proton & no
neutron (mass number = 1).
 It is represented by .H
1
1

D
1
2
2) Deuterium / Heavy Hydrogen (D)
 Deuterium constitutes 0.016% of total hydrogen
occurring in nature.
 The molecule of deuterium or heavy hydrogen is
diatomic D2.
 The nucleus of atom consist of single proton & a
 It is represented by .

3) Tritium (T)
 It is formed in upper atmosphere by certain nuclear
reaction induced by cosmic rays.
 It constitutes 1 part in 1021 parts of total hydrogen
available in nature.
 The molecule of Tritium is diatomic T2.
 The nucleus of atom consist of single proton & two
 It is represented by .

3) Tritium (T)
 It is radioactive in nature.
 Tritium decays by the loss of β particle to yield rare
but stable isotope of helium.
 The half-life period for this decay is 12.4 years.
 HeT
2
3
1
3

3) Tritium (T)
 It can be obtained by bombarding neutron on
isotopes of Lithium.
nHeTnLi
HeTnLi
0
1
2
4
1
3
0
1
3
7
2
4
1
3
0
1
3
6



Importance of Isotopes
1) Use of deuterium & tritium in nuclear energy
 Continuous production of tritium from lithium is important
step in the future generation of energy from nuclear fusion.
 In fusion reactor, tritium & deuterium are heated to give a
plasma in which the nuclei react to produce a neutron & .
 Energy obtained per unit mass of deuterium & tritium nuclei
is about 4 times than that from fission of Uranium & 10
million times than from petrol.
He
2
4

Nuclear Reaction of Deuterium & Tritium
MeVnHeTD 6.17
0
1
2
4
1
3
1
2


2) Heavy water (D2O) use as neutron moderator &
Coolant for nuclear reactors:
 Water containing deuterium instead of normal hydrogen
is called as heavy water.
 Ordinary water contains very small portion (about 1 part
in 5000) of D2O.
 Concentration of heavy water is increased by fractional
distillation / prolong electrolysis of water.

2) Heavy water (D2O) use as neutron moderator &
Coolant for nuclear reactors:
 D2O is used as moderator in the nuclear power industry.
 Neutrons are used for bringing about fission of Uranium
atoms but for this purpose, their speed should be slower
down.
 This is done by passing them through heavy water.
 It is also used as coolant for nuclear reactors.

3) Kinetic Isotope effect:
 Differences in the properties which arise from the
difference in mass are called as isotope effect.
 Rates of reactions are measurable different for the
process in which E-H & E-D bonds are broken, made or
rearranged (E – another element).
 The detection of this kinetic isotope effect help to
support a proposed reaction mechanism of many
chemical reactions.

4) Isotope effect in detection of motion of hydrogen:
 Frequencies of molecular vibrations depends on the masses of
atoms.
 As the masses of D & H are different, their frequencies of the
molecular vibrations are different.
 The heavier isotope (D) results in lower frequency.
 This isotope effect can be studied by IR spectra of H & D
substituted molecule to determine motion of H atom in the
molecule.

5) Isotopes as tracers:
 The distinct properties of isotopes makes them
useful as tracers.
 The involvement of H & D through a series of
reactions can be followed by IR & mass
spectroscopy.
 Tritium can be detected by its radioactivity.

6) Use in NMR (Nuclear Magnetic Resonance)
Spectroscopy:
 1H-NMR detects the presence of hydrogen nuclei
in compound & is powerful method for structure
determination of molecule, even like protein.
 Heavy water (D2O) is used as one of the
references in NMR spectroscopy.

7) Tritium in self powered lighting devices.
 Tritium is used in specialized self powered lighting
devices.
 The emitted electrons from radioactive decay of
small amount of tritium cause phosphors
(A phosphor, most generally, is a substance that
exhibits the phenomenon of luminescence) to
glow.

8) Tritium in nuclear weapon:
 Tritium is used as nuclear weapons to enhance
efficiency & yield of fission bombs.
 It is used in hydrogen bomb.

Methods of
Preparation
1. Laboratory Scale Preparation
2. Industrial Production
3. From Solar Energy

A. From Aqueous acid
 It is based on the principle of displacement of hydrogen
from its solution which follow hydrogen in
electrochemical series where metals are arranged in the
order of increasing ease of reduction.
2 Na(s) + H3O
+
(aq)2 2 Na
+
(aq) + H2(g) + 2 H2O(l)

A. From Aqueous acid
 On laboratory scale , the usual method is reaction of Zn
with dil H2SO4 / dil HCl.
Zn(s) + H2SO4
ZnSO4 + H2(g)
Zn(s) + 2 HCl ZnCl 2 + H2(g)

B. From alkali
 H2 can be prepared in laboratory scale by reaction of Al
or Si with hot alkali solution.
2 Al + 2 NaOH+ 6 H 2O Na[Al(OH) 4] + 3 H2

2. Industrial Production of H2
A. Production from fossil sources
 Hydrogen is produced in large amount by steam
reforming process.
 Production of hydrogen is often integrated directly
into chemical process that require H2 as a feed
stock.
 Most of the H2 for industry is produced by high
temperature reaction of H2O with CH4 or with coke.

a) Steam Reforming of methane:
Hydrocarbons such as methane (from natural gas) is
mixed with steam & passed over nickel catalyst at 700 –
1100oC to yield water gas (mixture of CO & H2).
Further reaction of water gas produces more H2 by water
gas shift reaction.
CH4 + H2O CO + 3 H2

Water Gas Shift Reaction
The gases emerging from the steam reformer are then mixed with
more steam cooled to 400oC & then are passes through shift
converter – an iron copper catalyst.
The CO2 so formed is easily removed either by dissolving in water
under pressure or reacting it with K2CO3 or by using aqueous solution
of various amines to remove CO2 forming solid ammonium carbonate.
CO + H2O CO2 + H2

b) Steam Reforming of coke:
Coke is obtained by carbonization of coal – the process of
heating coal to a high temperature in the absence of air to improve
quality as a fuel.
Hydrogen is made cheaply & in large amount by passing steam
over red hot coke. The product is water gas . The process takes
place at 1000oC.
It is difficult to separate H2 from CO. To produce more H2,
water gas is subjected to water gas shift reaction.
C + H2O CO + H2

c) Electrolysis of water
By electrolysis of water containing a small
amount of acid or alkali, hydrogen (H2) is liberated
at cathode while oxygen (O2) is liberated at anode.

Acidic medium:
H2SO4 2 H
+
+ SO 4
-2
H2O H
+
+ OH
-

At Cathode:
At Anode:
2 H
+
+ 2e
-
2 H.
H+ H H 2
4 OH
-
4 OH + 4 e
-
4 OH 2 H 2O + O 2

3. From Solar Energy:
 Water splitting is the general term for a chemical
reaction in which water is separated into oxygen &
hydrogen.
 Solar energy is utilized in several ways such as, wind
turbines, photosynthesis & photovoltaic cells.
 One such technology under development is high
temperature solar H2 production.

 High Temperature Solar H2 Production
 Single step thermal decomposition of water requires
temperature in excess of 4000oC, which is very high to
achieve & practically unsuitable.
 Sunbelt regions that receives solar power of about 1
kW/m2 are suitable for high temperature solar H2
production.
 Solar power concentration reflect & focus solar radiation
onto the receiver furnace, producing temperature in
excess of 1500oC.
 By using multistep process, it is possible to produce H2 at
lower temperatures.

 Reactions involved
2 Fe2O3(g) 6 FeO (s) +
1
/2 O2(g)
H2O(l) + 3 FeO (s) Fe 3O4(s) + H2(g)

Compounds of
Hydrogen
1. Molecular hydrides
2. Saline hydrides
3. Metallic hydrides
4. Intermediate hydride

Molecular Hydrides
 Molecular hydrides are the compounds of
hydrogen with p-block elements & beryllium.
 The compounds are formed by covalent bonds.
 The bond polarity varies depending on the electron
activity of the atoms to which H2 is attached.

Molecular Hydrides
A. Hydrocarbons
1. Methane

Molecular Hydrides
A. Hydrocarbons
1. Methane
• It is the simplest hydrocarbon.
• At room temperature & standard pressure, it is colourless,
odorless & flammable gas.
• It undergo combustion reaction as
• Apart from this combustion reaction, it is not very reactive.
CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)

Molecular Hydrides
A. Hydrocarbons
1. Methane
Occurrence
• It is the major component of natural gas about 87% by volume.
• Apart from gas fields, methane can be obtained via biogas
generated by fermentation of organic matter including manure,
wastewater sludge, etc under anaerobic conditions.
• It is created near the earth’s surface, primarily by micro-
organisms by the process of methanogenesis.

Molecular Hydrides
A. Hydrocarbons
1. Methane
Preparation
a) Laboratory scale preparation
• Methane can be produced by the destructive distillation
of acetic acid in presence of soda lime.
• Acetic acid is decarboxylated in this process.

Molecular Hydrides
A. Hydrocarbons
1. Methane
Preparation
a) Industrial scale preparation
1. Methane can be produced by hydrogenating CO2 through
the Sabatier process.
The process involves reaction of H2 & CO2 at elevated
temperature & pressure in the presence of Ni-catalyst to
produce methane & water.
CO2 + 4 H2 CH4 + 2 H2O

Molecular Hydrides
A. Hydrocarbons
1. Methane
Preparation
b) Industrial scale preparation
2. Methane is also side products of hydrogenation of CO in
Fischer-Topsch process.
It involves collection of chemical reactions that convert
the mixture of CO & H2 into hydrocarbons.
CO + 2 H2 CH4 + H2O

Molecular Hydrides
A. Hydrocarbons
1. Methane
Applications
a) It is used as domestic & industrial fuel. Methane in the form of
compressed natural gas is used as vehicular fuel. It is a clean
burning fuel. It may be transported as a refrigerated liquid.
b) It is important for electrical generation by burning it as a fuel in
a gas turbine or steam engine.
c) Chemical feedstock – in chemical industries, methane is
converted to synthesis gas, a mixture of CO & H2, by steam
reforming.

Molecular Hydrides
A. Hydrocarbons
1. Ethane

Molecular Hydrides
A. Hydrocarbons
1. Ethane
• It is aliphatic hydrocarbon.
• At STP, it is colourless, odorless gas.
• It undergo combustion reaction as
• It occurs in traces in earth’s atmosphere & sea.
2 C2H6 + 7 O2 4 CO2 + 6 H2O

Molecular Hydrides
A. Hydrocarbons
1. Ethane
Preparation
a) Laboratory scale preparation
• Ethane can be prepared by Kolbe’s electrolysis, In this
technique an aqueous solution of acetate salt is electrolyzed.
• At anode acetate is oxidized to produce CO2 & methyl radical &
highly reactive methyl radicals combine to produce ethane.

Molecular Hydrides
A. Hydrocarbons
1. Ethane
Preparation
CH3COO
-
CH 3 + CO 2 + e
-.
CH3 + CH 3 C 2H6
. .

Molecular Hydrides
A. Hydrocarbons
1. Ethane
Preparation
a) Industrial scale preparation
Ethane Is the second largest component of natural gas.
It is separated from methane by liquefying at cryogenic
temperatures, where gaseous methane can be separated
out.
Heavier hydrocarbons are separated by distillation.

Molecular Hydrides
A. Hydrocarbons
1. Ethane
Applications
a) It is mainly used in chemical industries in the production
of ethylene by steam cracking. It is a raw material for
polymer formation.
b) It can be used as a refrigerant in cryogenic refrigeration
system.
c) In scientific research, liquid ethane is used in cryo-
electron microscopy.

Molecular Hydrides
B. Silane
1. Silanes are saturated hydrosilicons in which Si atoms
is bonded to four other hydrogen atom by covalent
bond, thus having a tetrahedral structure. It is a
colorless gas.
2. Silanes are much more reactive than alkanes. SiH4 is
spontaneously flammable in air, reacts violently with
hydrogens & hydrolyzed in contact with water. The
increase reactivity as compared to hydrocarbons is
attributed to large atomic size of Si.

Molecular Hydrides
B. Silane
 Preparation
1. Laboratory scale preparation
a) Silane can be prepared by heating sand with Mg-powder
to produce Mg-silica which is then poured into 20% non-
aqueous solution of HCl to produce silane.
4 HCl + Mg2Si SiH 4 + 2MgCl2

Molecular Hydrides
B. Silane
 Preparation
b) Silane can be prepared by reducing SiCl4 with LiAlH4, the
method gives better yield.
SiCl4 + LiAlH4 SiH 4 + AlCl3 + LiCl

Molecular Hydrides
B. Silane
 Preparation
2. Industrial Scale Preparation
a) Commercially silane is prepared by the reaction of SiO2 with Al
under high pressure of hydrogen in a molten salt mixture of
NaCl & AlCl3
6 H2(g) + 3 SiO2(s) + 4 Al 3 SiH4(g) + 2 Al2O3(s)

Molecular Hydrides
B. Silane
 Preparation
b) Industrial method for preparation of very high purity silane,
suitable for use in semiconductor starts with metallurgical
grade silicon (Si), H2 & SiCl4. It involves a complex series of
redistribution reaction (in which byproducts are recycled in
process) & distillations.
6 H2(g) + 3 SiO2(s) + 4 Al 3 SiH4(g) + 2 Al2O3(s)

Molecular Hydrides
B. Silane
 Preparation
b) ---- Si + 2 H2 + 3 SiCl4 4 SiHCl3
2 SiHCl3 SiH2Cl2 + SiCl4
2 SiH2Cl2 SiHCl3 + SiH3Cl
2 SiH3Cl SiH4 + SiH2Cl2

Molecular Hydrides
B. Silane
 Preparation
c) It can also be prepared by the reaction of LiH with silicon
tetrachloride via Sundermeyer process.
4 LiH + SiCl4 4 LiCl + SiH4

Molecular Hydrides
B. Silane
 Preparation
d) Silane can be produced from metallurgical grade silicon in
two step process.
In 1st step, powdered Si is reacted with HCl at 300oC to
produce trichlorosilane along with H2 gas.
.In 2nd step, trichlorosilane is then boiled on resinous bed
containing of silane.
Si + 3 HCl HSiCl3 + H2
4 HSiCl3 SiH4 + 3 SiCl4

Molecular Hydrides
B. Silane
Applications
1. Silane is used in the production of semiconductor
devices such as solar cells. Silanes are used in applying
polycrystalline silicon layers on silicon wafers while
manufacturing semiconductors.
2. Low cost solar panels can be prepared by using silane
which is used for depositing amorphous silicon on glass
or other tubes.
3. It can be used as water repellants.

Molecular Hydrides
B. Silane
Applications
4. Silanes are used in masonry protection.
5. It is used as sealants.
6. It is used as coupling agents to adhere glass fibres to
a polymer matrix stabilizing the composite material.

Molecular Hydrides
C. Germane
It has applications in semiconductor industry.

Molecular Hydrides
C. Germane
1. It is the simplest germanium hydride & is the most
useful compound of Germanium.
2. It is having similar tetrahedral structure as that of
methane & silane. It is a colourless gas.
3. It burns in air to give GeO2 & water. They are similar
to silane, but are less volatile, less flammable & are
unaffected by water or aqueous acid or alkali.

Molecular Hydrides
C. Germane
 Preparation
On laboratory scale, germane can be prepared by reaction
of Na2GeO3 with sodium borohydride.
Na2GeO3 + NaBH4 + H2O GeH4 + 2NaOH + NaBO2

Molecular Hydrides
C. Germane
 Preparation
a) Chemical reduction method
By the action of reducing agent GeCl4 or GeO2
converts to GeH4.
GeO2 + NaBH4 GeH4 + NaBO2
GeCl4 + LiAlH4 GeH4 + LiCl + AlCl3

Molecular Hydrides
C. Germane
 Preparation
b) Electrochemical reduction method
It uses Ge metal as cathode & Mo or Cd as anode
immersed in aqueous electrolyte solution.
Ge & H2 gases evolve from cathode, while anode
reacts to form molybdenum oxide or cadmium oxide.

Molecular Hydrides
C. Germane
 Preparation
c) Plasma synthesis method
It involves bombarding Ge metal with H2 atoms that
are generated using high frequency plasma to produce
germane.

Molecular Hydrides
D. Ammonia
1. Ammonia or azane has a pyramidal structure.
2. Nitrogen undergoes sp3 hybridization. 3 of 4 hybrid
orbitals are used in forming 3 N-H bonds, while the
fourth is occupied by lone pair of electrons.
3. Due to larger lone pair-bond pair repulsion than
bond pair-bond pair repulsion, the molecule gets
little distorted.
4. It is a colorless gas with a characteristic pungent
smell.

Molecular Hydrides
D. Ammonia
5. Boiling point of NH3 is abnormally high as compared
to corresponding group elements which can be
attributed to the association of its molecule through
hydrogen bonding.
6. Nitrogen has lone pair of electrons which makes
ammonia basic in nature.
7. The shape makes it polar. The molecules polarity &
ability to form hydrogen bond, makes it miscible
with water.

Molecular Hydrides
D. Ammonia
 Preparation
On laboratory scale, ammonia is prepared by heating on
intimate mixture of NH4Cl & dry slapped line (CaO).
2 NH4Cl + CaO CaCl2 + H2O + 2 NH3

Molecular Hydrides
D. Ammonia
 Preparation
On industrial scale, ammonia is prepared by Haber’s
process.
N2 + 3 H2 2 NH3

Molecular Hydrides
D. Ammonia
Applications
1. About 75% of ammonia is used as fertilizer as its
salts or as a solution.
2. It is directly or indirectly the precursor to most
nitrogen containing compounds. Like for preparing
HNO3.
3. Ammonium hydroxide is used as general purpose
cleaner for many surfaces such as glass, porcelain,
stainless steel, etc

Molecular Hydrides
D. Ammonia
Applications
4. 16-25% solution of ammonia is used in fermentation
industry as a source of nitrogen for microorganisms
& to adjust pH during fermentation.
5. It has been used as the cooling liquid in refrigerator.
6. Liquid ammonia is often used as a cheaper & more
convenient way of transporting H2 than cylinders of
compressed H2 gas.

Saline Hydrides
 These are formed by metals which are more
electropositive than hydrogen. Such metals are of
group I & group II except Be & Mg.
 These are formed by transfer of electrons from
metal to hydrogen atom contains H- ions.
 e.g. LiH, NaH, CaH2, etc

Saline Hydrides
A. Lithium hydride
1. It is a colourless solid with high melting point.
2. It is insoluble in any solvent with which it does not
react.
3. It reacts rapidly with moist air forming Li(OH)2, LiO2
& Li2CO3.
4. It can ignite in air when heated slightly below
200oC.
5. LiH reacts with water vigorously, explosively
producing LiOH & H2.

Saline Hydrides
A. Lithium hydride
It is prepared by direct heating of lithium
metal with hydrogen gas at temperature above
600oC.
Increase in temperature or pressure, addition
of carbon upto 0.003%, increases the yield upto
98%.
2 Li + H2 2 LiH

Saline Hydrides
A. Lithium hydride
Applications
1. As it contains highest percentage of hydrogen, it is
used for storage of hydrogen but this application is
restricted because of high stability. Removal of H2
requires high temperature above 700oC.
2. It rarely acts as reducing agent except synthesis of
silanes & it can be used in the production of variety
of reagents like LiAlH4.
3. LiH is used for shielding in nuclear reactors.

Saline Hydrides
B. Sodium hydride
1. It is a colorless solid with high melting point.
2. It is insoluble in organic solvent.
3. It can ignite in air.
4. It gives explosively violent reaction with water.

Saline Hydrides
B. Sodium hydride
It is prepared by direct heating of sodium
metal with hydrogen gas at high temperature
close to 700oC.
2 Na + H2 2 NaH

Saline Hydrides
B. Sodium hydride
Applications
1. It acts as a strong reducing agent reducing various
compounds.
2. It can be used to dry some organic solvents because
of its quick & irreversible reaction with water.
3. NaH pellets when crushed in the presence of water
releases H2. Therefore NaH is proposed for H2
storage for the use in fuel cell vehicles.
4. It is used for preparing NaBH4.

Storage
of
Hydrogen
A. Chemical Storage: In the form of metal hydride
as Sodium Alanates
B. Physical Storage: via compression, liquification,
adsorption on porous carbon materials.

Storage of Hydrogen
 For stationary storage of hydrogen, it is
consumed in refineries & chemical plants where it
is produced.
 For the use of hydrogen as a fuel in vehicles, ‘on
board’ storage of hydrogen has been the main
challenge.

A. Chemical Storage
 Alanates are complex metal hydrides, which
have a potential for a high hydrogen capacity.
 Sodium alanate (NaAlH4) is a promising material
for H2 storage with capacity of 5.5 wt %.
 It is one of the known complex hydride with
favorable thermodynamics & acceptable
gravimetric storage capacity for use in PEM fuel
cell which operates at about 80oC.

A. Chemical Storage
It is released from NaAlH4 in the following
steps:
1. As 1 atm pressure, the first reaction between
thermodynamically favorable at temperature
above 33oC & release 3.7 wt % H2.
NaAlH4(s) Na3AlH6(s) + 2 Al(s) + 3 H2(g)

A. Chemical Storage
2. The 2nd reaction takes place above 110oC & can
release 1.8 wt % H2.
Reversibility kinetics of NaAlH4 is improved
upon addition of Ti &/or Zr dopants which causes
in primary crystal size.
Rehydrogenation is preferably done at 10
MPa pressure & temperature slightly above 100oC
2 Na3AlH6(s) 6 NaH(s) + 2 Al(s) + 3 H2(g)

Limitations of Sodium Alanates
1. It contains low H2 capacity, slow uptake.
2. H2 release proceeds in stages which is not ideal
for applications.
 It helps for fundamental understanding,
designing & developing improved types of
complex metal hydrides.

B. Physical Storage
 Physical adsorption of H2 on porous carbon material
is one of the main methods being considered for
automobile applications.
 It can be done in several forms of carbon like
amorphous activated carbon, graphite, nanotubes,
etc.
 e.g. Based on surface area of single graphene sheet
(1315 m2/g), the storage capacity of hydrogen
adsorbed on graphene is about 3.3 % by weight at
cryogenic temperature.

B. Physical Storage
 Carbon nanomaterials possesses small size, high
surface area, porosity & low density.
 Carbon nanomaterials can be discussed in
different forms as:
1. Fullerene
2. Single walled carbon nanotubes
3. Multiwalled carbon nanotubes
4. Carbon & Graphite nanofibres

1. Fullerenes
 Fullerenes are closed cage carbon molecules
composed of sp2 hybridized carbon atoms.
 Spherical fullerene (C60) are often referred to as
‘bucky balls’ consisting of 20 hexagon & 12
pentagons.
 C60 can be hydrogenated & dehydrogenated
reversibly.
 C60H36 contains approximately 5 wt % hydrogen.
 H2 can also be stored within fullerene framework.

2. Single walled carbon nanotubes (SWNT)
 SWNT’s is like single rolled sheet of graphene.
 It has a narrow porous size which makes them
attractive as adsorbents of H2.
 H2 uptake increases with surface area which
increases with tube diameter.
 Under 1 atm pressure, the amount of H2
adsorbed in SWNT’s is small (< 1 wt %) where as,
under cryogenic conditions from 1 – 2.4 wt %.

2. Single walled carbon nanotubes (SWNT)

3. Multiwalled carbon nanotubes (SWNT)
 MWNT’s consist of layers of concentric cylinders
of graphene with hollow center.
 The spacing between each cylinder is similar to
the interplanar distance in graphite, with number
of cells varying from 2 to 50.
 MWNT’s are inactive for H2 storage, but alkali
doped MWNT’s can store H2 of 7.2 wt %.

3. Multiwalled carbon nanotubes (MWNT)

4. Carbon & Graphite Nanofibres
 Carbon nanofibres (CNF’s) are layered graphitic
nanostructures.
 The reported values of hydrogen storage
capacity of such structures ranged from < 1 wt %
to several tens of weight percentage at moderate
temperature & pressure.

4. Carbon & Graphite Nanofibres
 Graphite nanofibres (GNF’s) consists of the
stacks of graphene plates & cones, have plenty of
open edges that can favor H2 adsorption.
 GNF produced by pyrolysis of acetylene adsorb
6.5 wt % H2.

Chemistry of hydrogen and its advancements.

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