HYDROGEN
UNIT 9
Made By – Manas Mahajan
H
H
H2
HYDROGEN
Hydrogen has the simplest atomic structure among all the
element. However, it exist in diatomic (H2) form in nature and is the
lightest and most abundant chemical element, constituting roughly 75%
of the universe’s chemical element mass but is still the rarest element
on the earth about 0.15% by mass. The name hydrogen is arrived from a
Greek HYDRO meaning water and GENES meaning creator.
By R. Gautham
DISCOVERY
In 1671, Robert Boyle discovered and described the reaction
between iron filings and dilute acids, which results in the production of
hydrogen gas.
In 1766, Henry Cavendish was the first to recognize hydrogen gas as a
discrete substance, by naming the gas from a metal-acid
reaction "flammable air“.
He speculated that "flammable air" was in fact identical to the
hypothetical substance called "phlogiston" and further finding in 1781 that
the gas produces water when burned.
In 1783, Antoine Lavoisier gave the element the name HYDROGEN when
he and Laplace reproduced Cavendish's finding that water is produced
when hydrogen is burned.
POSITION OF HYDROGEN
IN THE PERIODIC TABLE
Hydrogen is the first element in the periodic table. Hydrogen
has electronic configuration 1s1. On the other hand like alkali
metals , it is short by one electron to the corresponding
noble gas configuration , helium (1s2). Hydrogen therefore
has a resemblance to alkali metals, as well as with halogens.
Loss of electron from hydrogen atom results in nucleus (H+)
of ~1.5×10-3pm size which is extremely small. As a sequence,
H+ does not exists freely and is associated with other atoms
or molecule. Thus ,it is a unique ability and is therefore
placed separately.
Isotopes of Hydrogen
Hydrogen has three naturally occurring isotopes, denoted 1H, 2H and 3H.
Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not
observed in nature. Harold C. Urey was awarded Nobel prize to separate these.
1H
is the most common hydrogen isotope with an abundance of more than 99.98%.
Because the nucleus of this isotope consists of only a single proton, it is given the
descriptive but rarely used formal name protium.
2H,
the other stable hydrogen isotope, is known as deuterium and contains one
proton and one neutron in its nucleus. Essentially all deuterium in the universe is
thought to have been produced at the time of the Big Bang, and has endured since
that time. Deuterium is not radioactive, and does not represent a significant
toxicity hazard. Water enriched in molecules that include deuterium instead of
normal hydrogen is called heavy water. Deuterium is also a potential fuel for
commercial nuclear fusion.
3H
is known as tritium and contains one proton and two neutrons in its nucleus. It is
radioactive, decaying into helium-3 through beta decay with a half-life of 12.32
years. It is so radioactive that it can be used in luminous paint, making it useful in
such things as watches.
PREPARATION OF DIHYDROGEN
Laboratory preparation of Dihydrogen
 It is usually prepared by the reaction of granulated zinc with
dilute hydrochloric acid.
Zn + 2H+
Zn2+ + H2
 It can also be prepared by the reaction of zinc with aqueous
alkali.
Zn + 2NaOH
Na2ZnO2 + H2
Sodium zincate
Commercial Production of Dihydrogen
• Electrolysis of acidified water using platinum electrodes
gives hydrogen
Electrolysis
2H2O(l)
2H2(g)+O2(g)
Traces of acid/base
• High purity(>99.95%) dihydrogen is obtained by
electrolysing warm aqueous barium hydroxide solution
between nickel electrodes.
• It is obtained as a byproduct in the manufacture of sodium
hydroxide and chlorine by the electrolysis of brine solution.
2Na+(aq)+2Cl-(aq)+2H2O(l)
Cl2(g)+H2(g)+2Na+(aq)+2OH-(aq)
• Reaction of steam on hydrocarbons or coke at high
temperature in the presence of catalyst yields hydrogen.
CH4(g)+H2O(g) 1270K
CO(g)+3H2(g)
Ni
• Water spontaneously dissociates at around 2500°C, but
this occurs at temperatures too high for usual process
piping and equipment so catalysts are required to reduce
the dissociation temperature. This method is called
thermolysis.
Presently ~77% of the industrial dihydrogen is produced
from petro-chemicals, 18% from coal, 4% from electrolysis of
aqueous solution and 1% from other sources
PROPERTIES OF DIHYDROGEN
Physical properties
Dihydrogen is a colourless,
odourless, tasteless,
combustible gas. It is lighter
than air and insoluble in water.
• Chemical properties
1. Reaction with halogen
H2(g)+X2(g)catalyst or heating2HX(g) (X= F, Cl, Br, I)
2.
Reaction with dioxygen
H2(g)+O2(g)673K,200atm
Fe 2H2O(l)
3.
Reaction with dinitrogen
3H2(g)+N2(g)
2NH3(g)
4. Reaction with metals
H2(g)+2M(g)
2MH(s) (M is an alkali metal)
5. Reaction with metal ions and metal oxides
H2(g)+Pd2+(aq)
Pd(s)+2H+(aq)
yH2(g)+MxOy(s)
xM(s)+yH2O(l)
6. Reactions with organic compounds
i. Hydrogenation of vegetable oils using nickel as catalyst
gives edible fats.
ii. Hydroformylation of olefins yields aldehydes which
further undergo reduction to give alcohols.
H2+CO+RCH=CH2
RCH2CH2CHO
H2+RCH2CH2CHO
RCH2CH2CH2OH
USES OF DIHYDROGEN
• The largest single use of dihydrogen is in the
synthesis of ammonia which is used in the
manufacture of nitric acid and nitrogenous fertilizer.
• Dihydrogen is used in the manufacture of
polyunsaturated vegetable oils like soyabean, cotton
seeds etc.
• It is used in the manufacture of bulk organic
chemicals, particularly methanol.
CO(g)+2H2(g)
CH3OH(l)
 It is widely used for the manufacture of metal hydrides.
 It is used for the preparation of hydrogen chloride, a highly
useful chemical.
 In metallurgical processes, it is used to reduce heavy metal
oxides to metals.
 It is used as a rocket fuel is space research.
• Atomic hydrogen and oxy-hydrogen torches find use for
cutting and weilding purposes. Atomic hydrogen atoms are
allowed to recombine on the surface to be weilded to
generate the temperature of 400K.
• Dihydrogen is used in fuel cells for generating electrical
energy. It has many advantages over the conventional fossil
fuels and electric power. It does not produce any pollution
and releases greater energy per unit mass of fuel in
comparison to gasoline and other fuels.
HYDRIDES
What are hydrides?
When dihydrogen Combines with other elements
to form various compounds, that compounds are
called as hydrides.
HYDRIDES
IONIC OR
SALINE
HYDRIDES
COVELENT OR
MOLECULAR
HYDRIDES
METALLIC
HYDRIDES
IONIC HYDRIDES
• These hydrides are form from s-block elements.
• Are highly electropositive in character.
• These are crystalline, non-volatile, non-conducting in
solid state.
• Saline hydrides react violently with water to produce
dihydrogen gas.
• KH(S) + H2O(q)
H2 (g) + 2electrons.
• Stability of the hydrides decreases down the group I
and II.
• Lithium hydrides is rather unreactive at moderate
temperature with Cl2 and O2.SO so it is used to
synthesize other useful hydride.
COVALENT HYDRIDES
- Dihydrogen forms molecular compounds with
most of the p-block elements, for e.g.
H2O CH4 NH3.
- Volatile compounds
- These hydrides are further classified according
to the relative numbers of electrons and bonds in
their Lewis structure.
COVELENT
HYDRIDES
ELECTRON
DEFICIENT
ELECTRON
PRECISE
ELECTRON RICH
HYDRIDES
ELECTRON DEFICIENT
 These hydrides have very few electrons for
writing its conventional Lewis structure.
 Boron family (group 13) forms electron
deficient compounds.
 These hydrides behave as Lewis acid i.e.
electron pair acceptor.
 Example : Diborane
ELCTRON PRECISE HYDRIDES




Carbon family forms such types of hydrides.
Compound have tetrahedral geometry.
Example :CH4
These hydrides have the required numbers of
electrons to write their conventional Lewis
structure.
ELCTRON RICH HYDRIDES
 These hydrides have excess number of
electrons (lone pairs).
 Nitrogen family, oxygen family and fluorine
family forms these type of hydrides.
 These compounds behaves like Lewis bases.
 Presence of lone pairs of electrons on highly
electronegative elements like N, O and F
results in hydrogen bonding.
 Examples: NH3 and H2O
METALLIC HYDRIDES
 These are formed by many d-block
elements and f-block elements.
 However Mn, Fe and Cobalt family do not
form hydrides.
 Only 7th group forms these hydrides like
CrH.
 These hydrides conduct heat and
electricity.
 These are nonstoichiometric and deficient
in hydrogen.
 Example : TiH1.8-2, LaH2.87.
Examples:
• nickel hydride: used in NiMH batteries
• palladium hydride: electrodes in cold fusion experiments
• lithium aluminium hydride: a powerful reducing agent used in organic
chemistry
• sodium borohydride: selective specialty reducing agent, hydrogen storage in
fuel cells
• sodium hydride: a powerful base used in organic chemistry
• diborane: reducing agent, rocket fuel, semiconductor dopant, catalyst, used
in organic synthesis; also borane, pentaborane and decaborane
• arsine: used for doping semiconductors
• stibine: used in semiconductor industry
• phosphine: used for fumigation
• silane: many industrial uses, e.g. manufacture of composite materials and
water repellents
• ammonia: coolant, fuel, fertilizer, many other industrial uses
• hydrogen sulfide: component of natural gas, important source of sulphur
• Chemically, even water and hydrocarbons could be considered hydrides.
A notable thing is that all solid non-metallic & metalloid hydrides are highly
flammable. But, when Hydrogen combines with halogens, it produces acids
rather than hydrides and they are not flammable.
Natural occurrence:
 Rain water: Purest form of natural water.
 Sea water: It is an impure form of water.
 Surface water: Include streams, rivers and lakes and
are most important sources of water for all purposes.
In a hydrogen compound, when hydrogen is bonded with highly electronegative
atom (F,O,N) by a covalent bond, electron pair is attracted towards
electronegative atom so strongly that a dipole results i.e., one end carries a
positive charge (H-end) and other end carries a positive charge (X-end).
If a number of such molecules are brought nearer to each other, the positive
end of one molecule and the negative end of the other molecule will attract
each other and weak electrostatic force will develop. Thus, these molecules will
associate together to form a cluster of molecules.
In water, there is INTERMOLECULAR H-BONDING:
This type of hydrogen bonding increases
the boiling point of the compound and
also its solubility in water. Increase in
boiling point is due to association of
several molecules of the compound.
Two bond pairs and two lone pairs
Colourless, tasteless and odourless.
o
o
 Freezes at 0 C and boils at 100 C.
o
 Maximum density is 1.00gcm-3 at 4 C.
 Polar molecule, V-shaped structure.
 Has a high dielectric constant. (78.39)
 Poor conductor of electricity.
 Tendency to associate.
 Universal solvent.
 High values of specific heat, latent heat of fusion and latent heat of
vapourisation.

1. NATURE:
 Water is neutral in nature.
1. Reaction with metals:
 Reacts with active metals and evolves hydrogen.
 It is decomposed by metals like Zn, Mg, Fe, etc., when
steam is passed over hot metals.
3.



Reaction with non metals:
Fluorine decomposes cold water.
Chlorine decomposes cold water forming HCl and HClO.
When steam is passed over red hot coke , water gas is
formed.
4. Action on nonmetallic oxides:
 Acidic oxides combine with water to form acids.
5. Action on metallic oxides:
 Basic oxides combine with water to form alkalies.
6. Action on hydrides, Carbides, Nitrides, Phosphides:
 Water decomposes these compounds with liberation of hydrogen,
acetylene (or methane), ammonia, phosphine resp.
7. Hydrolysis:
 Many salts, specially the salts of strong bases with weak acids, weak
bases with strong acids and weak bases with weak acids undergo
hydrolysis in water.
 Some salts on hydrolysis form oxy compounds.
8.

Decomposition:
Water containing either alkali or acid when electrolysed gets
decomposed into H2 and O2.
9.

Water of crystallisation:
It combines with many salts during crystallisation to form hydrates
10.Water as a catalyst:
 Water acts as a catalyst in many reactions. Perfectly dry gases
generally do not react but the presence of moisture brings the
chemical change. Ammonia and hydrochloric acid gas combine
only in the presence of moisture.
*******************************************
HEAVY WATER, D20
• It is used as a moderator in nuclear
reactors to study the nuclear
mechanisms.
• It can be prepared by exhaustive
electrolysis of water .
• It can also be formed as a by product
in some fertilizers.
•It is not radioactive .
• It is used for preparation of other
deuterium compounds.
• EXAMPLES:CaC2 + 2D20
SO3 + D2O
C2D2 + Ca(OD)2
D2SO4
Hydrogen peroxide
Methods of preparation
1. From Barium peroxide
BaO2 .8H2O  H2SO4 
 BaSO4  8H2O  H2O2
Barium sulphate is filtered off leaving behind H2O2.
2. By electrolysis of 50% H2SO4
H2SO4
At cathode
At Anode
electrolysis
H  HSO4
2H  2e  H2
2HSO4 
H2S2O8  2H2O
H2S2O8  2e
Peroxydisulphuric acid
distilled

at reduced pressure
H2O2  2H2SO4
H2O2 distills first leaving behind the H2SO4 which is recycled.
3. By auto oxidation of 2ethylanthraquinol
OH
O
C2H5
C2H5
air (O2)
OH
2-ethyl anthraquinol
O
2-ethyl anthraquinone
The H2O2 obtained by this method is further concentrated by distillation
under reduced pressure.
Structure of hydrogen peroxide
Structure and dimensions of the
H2O2molecule in the gas phase…
... and in the solid (crystalline) phase.
Oxidising properties
(i) 2FeSO4  H2 SO4  H2 O2  Fe2 (SO4 )3  2H2 O
(ii) H2 SO3  H2 O2  H2 SO4  H2 O
(iii) PbS  4H2O2 
 PbSO4  4H2O
Black
White
Oxidising properties
(iv) 2K4 Fe(CN)6   H2SO4  H2O2
2K3 Fe(CN)6   2H2O  K2SO4
(v) C6H6  H2 O2  C6H5 OH  H2
Phenol
(vii) NaNO2  H2O2 
 NaNO3  H2O
(viii) K2Cr2O7  H2SO4  4H2O2 
 K2SO4  CrO5  5H2O
Reducing properties
(i) H2O2  O3 
 H2O  O2
(ii) Ag2O2  H2O2 
 2Ag  H2O  O2
(iii) PbO2  2HNO3  H2O2 
 Pb(NO3 )2  2H2O  O2
Reducing properties
(iv) 2KMnO4  3H2SO4  5H2O2
K2SO4 2MnSO4  8H2O  5O2
(v) Cl2  H2O2 
 2HCl  O2
(vi) 6KAuCl4  3H2O2 
 2Au  2KCl  6HCl  3O2
Acidic properties
It reacts with alkalies and decomposes carbonates.
H2O2  2NaOH 
 Na2O2  2H2O
H2O2  Na2CO3 
 Na2O2  H2O  CO2
One of the most common uses of hydrogen peroxide is as a disinfectant. Spray some
hydrogen peroxide on surfaces like kitchen counter top and wipe with a clean rag.You may
even use it to disinfect your cutting board.
Hydrogen peroxide can be used as a mouthwash too.You have to dilute the chemical
with water and use it for rinsing the mouth. This mouthwash is also said to whiten teeth.
Ensure that you do not swallow the liquid, while rinsing.
Some farmers use hydrogen peroxide as an insecticide. They spray diluted form of this
chemical, on plants, so that the pests and weeds get killed, without causing harm to the
plants.
As rocket fuel.
For bleaching silk, wool, hair and leather
Do you know?
H2O2 is stored in the bottles lined with wax because…
The rough glass surface causes the decomposition of hydrogen peroxide.
35% Hydrogen Peroxide is used world wide in municipal water supplies
instead of chlorine to disinfect and stop the growth of unwanted organisms.
Do you have pure water?
DID YOU KNOW?
Store in a cool, dry place away from sunlight and other sources of
heat.
Always use non-metallic utensils.
Do not allow contact with easily burnable materials, such as paper.
Always store hydrogen peroxide in the container supplied.
Replace cap immediately after use - it is important that nothing
gets in to the container as this may lead to the hydrogen peroxide
breaking down which could result in explosions.
Store securely.
Always wear suitable protective gloves.
Avoid contact with eyes and face.
Do not use on damaged or sensitive skin.
Wash any residues down the drain with plenty of water.
Do not burn.
If hydrogen peroxide gets into the eyes
or on the skin, rinse immediately with
plenty of water. If the symptoms persist,
or if it is swallowed, seek medical
attention
immediately.
Always use water to dilute and mop up
spillages.
How do we find the normality of given value of
H2O2 ?
10 volume hydrogen peroxide means that 1 ml of such a solution of
hydrogen peroxide on heating will produce 10 ml of oxygen at N.T.P.
2H2O2 
 2H2O  O2
2(2 + 32) gm
22.4L at N.T.P.
= 68 gm
or 22400 cm3 at N.T.P.
 22400 ml of O2 is liberated from = 68 gm of H2O2
Solution
 10 ml of O2 is liberated from=
68
 10 gm of H2O2
22400
But 10 ml of O2 at N.T.P. are produced from 1 ml of 10 volume H2O2
solution.
 1 ml of 10 volume H2O2 solution contains =
68
 10 gm of H2O2
22400
= 0.03035 gm
 100 ml of 10 volume H2O2 solution contains
= 0.03035 × 100
= 3.035 gm
= 3.035%
DIHYDROGEN AS FUEL…
• It releases large quantity of heat when
combusted.
•It can release more energy than petrol.
• Pollutants in dihydrogen when
combusted are less than pollutants in
petrol.
LIMITATIONS…………
•A cylinder of compressed Dihydrogen
weighs about 30 times as much as a
tank of petrol containing the same
amount of energy.
•Dihydrogen gas is converted into liquid
state by cooling to 20k (requires
expensive insulated tanks) .
Hydrogen economy:- an alternative
and uses.
•Its basic principle is the
transportation and storage of energy
in the form of liquid dihydrogen.
•Dihydrogen is mixed in CNG for use
in four wheeler vehicles.
•It is also used in fuel cells for
generation of electric power..