Chemistry
Hydrogen
Session opener
What do you understand by word
“Hydrogen” ?
Hydrogen in Greek means
Water producer
Session Objectives
Session objective
1. Position of Hydrogen in periodic table
2. Isotopes of hydrogen
3. Methods of preparation, properties and
uses of dihydrogen.
4. Hydrides
5. Water — physical and chemical properties
6. Hardness of water and methods to remove it.
7. Heavy water
Session objective
9. preparation, properties and uses of
hydrogen peroxide.
10.Hydrogen economy
11.Uses of hydrogen as a fuel
12.Hydrazone
Session opener
Hydrogen in Greek means “water producer”
Position of Hydrogen in Periodic
Table
•
lightest element known having
atomic number 1.
•
Dihydrogen
•
The position of hydrogen is
anomalous in periodic table
Alkali metals
Halogens
• In modern periodic table it is located
in first group.
Resemblance with alkali metals
1. Electronic configuration
1
H

1s
1
2
2
6
1
Na

1s
,
2s
,
2p
,
3s
11
2
2
6
2
6
1
K

1s
,
2s
,
2p
,
3s
,
3p
,
4s
19
2. Electropositive character
H+, Na+, K+ etc.
3. Oxidation state: +1
Resemblance with halogens
1. Electronic configuration:
Both contain one electron less than
the nearest noble gas configuration
1
H

1s
near to 2He 
1
2
2
5
F

1s
,
2s
,
2p
near to 8 Ne 
9
2
2
6
2
5
Cl

1s
,
2s
,
2p
,
3s
,
3p
near to 18 Ar 
17
2. Non-metallic character:
Typical non-metals.
3. Atomicity:
Diatomic molecules.
4. Formation of similar types of
compounds
i. Halides: CCl4, SiCl4, GeCl4
ii. Hydrides: CH4, SiH4, GeH4
5. Oxidation state:
1 1
Na H
–1
1 1
Na Cl
Isotopes of hydrogen
Methods for commercial
production of dihydrogen
1. Electrolysis of water
electrolysis
2H2O 

–  2H2  O2
H / OH
2. By partial oxidation of hydrocarbons
673 K
CO  H2O 
 CO2  H2
Fe2 O3
Methods for commercial
production of dihydrogen
3. Water gas shift reaction
673 K
CO  H2O 
 CO2  H2
Fe2 O3
By Lane process
(1) Oxidation stage
3Fe  4H2O(g)
1025 - 1075 K
Fe3O4  4H2
(2) Reduction stage
Fe3O4  2H2  CO  3Fe  2H2O  CO2
water gas
Bosch process
Fe2O3 / Cr2O3
Re d hot coke  steam  water gas 

CO  H2 
Cold water
CO2  H2 
underpressure
steam, 770 K
CO2 dissolves + H2 is collected
1270 K
C  H2O(g) 
 CO  H2
Water gas
Fe O / Cr O
2 3
2 3
CO  H2  H2O 
 CO2  2H2
Water gas
Steam
770 K
Laboratory preparation of
hydrogen
Zn + dil H2SO4
ZnSO4 + 2H2O + SO2
Chemical properties:Not very reactive due to high bond dissociation
energy (435.88 kJ mol-1 at 298.2 K)
Ask yourself?
Can we use concentrated sulphuric acid and pure
zinc in the preparation of dihydrogen?
Zn  dil. H2SO4 
 ZnSO4  H2
(a) Conc. H2SO4 cannot be used because it acts as
oxidizing agent also and gets reduced to SO2.
Zn  2H2SO4 (conc.) 
 ZnSO4  2H2O  SO2
(b) Pure Zn is not used because it is non-porous
and reaction will be slow. The impurities in Zn help
in constitute of electrochemical couple and speed
up reaction.
Chemical properties
(i) Combustion:- It burns with pale blue flame
2H2 (g) + O2 (g)
2H2O(l)
(ii) Reaction with nitrogen
673 K, 200 atm
3H2 (g) + N2 (g) 
 2NH3 (g)
Fe
(iii) Reaction with oxygen
970 K
2H2(g)  O2(g) 
 2H2O(g)
Chemical properties
(iv)
Reaction with metals
Reactive metals like Na, K, Ca, Li
525 K
Ca  H2 
 CaH2
Metals like Pt, Pd, Ni form interstitial hydrides by
absorbing large volume of hydrogen. Such hydrogen
is called ‘occluded hydrogen’
(v)
Reaction with metal oxides:-
Hydrogen reduces oxides of less active
metals to corresponding metal
Δ
Fe3O4 + 4H2  3Fe + 4H2O

CuO  H2  Cu  H2 O
Ortho and para hydrogens
Ortho hydrogen
Para hydrogen
At room
temp.
75%
stability
more stable
•Different physical properties
•Similar chemical properties.
25%
less stable
Atomic hydrogen
3270 K
H2(g) 
2H (g)
H   435.9 kJ
Atomic hydrogen
• Highly reactive.
• Half life period is 0.3 sec.
Nascent hydrogen
•
The hydrogen produced in contact with the
substance to be reduced is known as ‘nascent
hydrogen’.
•
It is very reactive form of hydrogen
•
Better reducing agent than ordinary dehydrogen.
Structure of water
O
95.7 pm
104.5°
H
H
Gaseous state
H
H
H
H
O
O
O
H
Solid state
H
H
Structure of ice
H
O
H
H
H
O
H
O
H
H
O
O
H
H
H
H
H
O
O
O
H
H
H
H
H
O
H
Vacant space
Hard water
Contains dissolved salts of bicarbonates,
sulphates and chlorides of calcium and
magnesium.
Hard water does not produce lather
with soap solution.
Soft water
Soft water is free from bicarbonates,
sulphates and chlorides of calcium and
magnisum. It produce lather with soap
solution easily.
e.g., distilled water, rain water
Types of hardness
The hardness of water is of two types
(i)Temporary hardness
• due to presence of soluble bicarbonates of
calcium and magnesium.
• can be removed by simple boiling.
(ii)Permanent hardness
• due to presence of chlorides and sulphates of
calcium and magnesium.
• requires treatment of water to remove this type
hardness.
Do you know?
• Temporary hardness is also called carbonate
hardness
• Permanent hardness is also called non-carbonate
hardness
Softening of water
The process of removal of Ca2+
and Mg2+ ions from water is
called softening of water.
Removal of temporary hardness:
(i) M HCO3 2 
 MCO3  H2O  CO2
So lub le
inso lub le
(M = Ca or Mg)
Clark’s method or calcium hydroxide method
Ca HCO3 2  Ca(OH)2 
 2CaCO3  2H2O
Soluble
insoluble
Mg HCO3 2  2Ca(OH)2 
 2CaCO3  Mg OH2  2H2
Soluble
insoluble
insoluble
Removal of permanent hardness
(i) By washing soda (Na2CO3.10H2O)
treatment
CaCl2  Na2 CO3  CaCO3  2NaCl
insoluble 
MgSO4  Na2 CO3  MgCO3  Na2 SO4
insoluble
Removal of permanent hardness
ii)By using inorganic cation exchanger
(permutit method or Zeolite method):
Na2 Al2 Si2 O8  CaCl2  Ca  Al2 Si2 O8 2  2NaCl
Zeolite
settles at bottom
The zeolite can be regenerated by
treatment with sodium chloride
solution.
Ca  Al2Si2O8 2  2NaCl 
 Na2 Al2Si2O8  CaCl2
Removal of permanent hardness
(iii)
By organic ion exchanger:
Cation exchanger
Mg2 

2H  re sin

 Mg (resin)2  2H
2H  re sin

 Ca (resin)2  2H
In hard water  Cation exchanger 
Ca2 

Hard water  Cation exchanger 
Anion exchanger
SO24 
Hard water 
Cl

Hard water 
2HO  resin
 Anion exchanger 

HO  resin

 SO4  resin2  2OH
 Anion exchanger 

 Cl  re sin  OH
Ca resin2  2HCl 

Exchausted resin
Cl  re sin
Exchausted resin
2H  re sin
 CaCl2
Re generated resin
 NaOH 

HO  re sin
 NaCl
Re generated resin
Hydrogen peroxide
Methods of preparation
1.
Na2O2
ice cooled
20%

solution
 H2SO4 
 Na2SO4 
H2O2
30% solution
2. From Barium peroxide
BaO2 .8H2O  H2SO4 
 BaSO4  8H2 O  H2O2
Barium sulphate is filtered off leaving behind H2O2.
3. By electrolysis of 50% H2SO4
H2SO4
electrolysis
At cathode
At Anode
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.
4. By auto oxidation of 2ethylanthraquinol
O
OH
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.
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
Uses of hydrogen peroxide
1.
For bleaching silk, wool, hair and leather
2.
As rocket fuel
3.
Dilute solution is sold in name ‘perhydrol’
Do you know?
H2O2 is stored in the bottles lined with wax
because…
The rough glass surface causes the decomposition
of hydrogen peroxide.
Volume strength of hydrogen
peroxide (solved example 1)
Calculate the percentage strength of a
10 volume H2O2 solution.
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
= 68 gm
22.4L at N.T.P.
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 = 0.03035 gm
22400
 100 ml of 10 volume H2O2 solution contains
= 0.03035 × 100
= 3.035 gm
= 3.035%
Volume strength of hydrogen
peroxide (solved example 2)
Calculate the normality of
30 volume of H2O solution:
2H2O


2H2O  O2
2(2 + 32) gm
22.4L
= 68 gm
22.4 L of O2 is produced from = 68 gm of H2O2
 30 L of O2 is produced from =
 Strength of 20 volume H2O2 solution = 91.07 gm/mL
2 H2O2 

68 parts by weight
2 H2O  O2
32 parts by weight
Solution
32 parts by weight of oxygen is
obtained from = 68 parts by weight of H2O2
 32 parts by weight of oxygen is obtained from =
68
68 parts by weight of H2O2 
 8  17
32
 Equivalent weight of H2O2 = 17
Normality 
Strength
91.07

 5.35
Equivalent weight
17
Structure of hydrogen peroxide
H
H
95.8 pm
95.0 pm
147.5 pm
147.8 pm
90.2°
90.2°
101.9°
101.9°
H
H
Gas phase
Solid phase
Structure of hydrogen peroxide
Illustrative example
Calculate the normality of 30 volume
of H2O solution:
Solution:
2H2O


2(2 + 32) gm
= 68 gm
2H2O  O2
22.4 L
22.4 L of O2 is produced from = 68 gm of H2O2
68
 30 L of O2 is produced from 
 30 gm
22.4
 Strength of 20 volume H2O2 solution = 91.07 gm/mL
solution
2H2 O2

68 parts by weight
2H2 O  O2
32 parts by weight
32 parts by weight of oxygen is obtained from
= 68 parts by weight of H2O2
68
 8  17
parts by weight of oxygen is obtained from =
32
 Equivalent weight of H2O2 = 17
Normality 
Strength
91.07

 5.35
Equivalent weight
17
Heavy Water (D2O)
•
Was discovered by Urey in 1932.
•
Ordinary water contains one part of
heavy water in 600 parts of it.
•
Used as moderator in nuclear reactions.
•
Used as tracer in study of mechanism of
physiological process.
•
Used in preparation of deuterium
compounds.
Hydrogen economy (Hydrogen as fuel)
With advancement of science and
technology we realise in order to make
our lives comfortable fossil fuels are
depleating at an alarming rate and will
be exahausted soon. The electricity
cannot be stored to run automobiles.
It is not possible to store and transport
nuclear energy. Hydrogen is another
alternative source of energy and hence
called as ‘hydrogen economy’.
Hydrogen has some advantages as fuel
Hydrogen economy (Hydrogen as
fuel)
• Available in abundance in combined
form as water.
• On combustion produces H2O. Hence
pollution free.
• H2-O2 fuel cell give more power.
• Excellent reducing agent. Therefore
can be used as substitute of carbon in
reduction for processes in industry.
Obstacles in hydrogen economy
Transportation:
Hydrogen gas is explosive and hence it is
difficult to store and transport.
Formation of hydrogen from H2O:
The cheaper production of the hydrogen is basic
requirement of hydrogen economy which is not
possible now.
The main aim and advantage of hydrogen economy is
to transmit energy in four of hydrogen.
Thank you