Hydrogen and its compounds

Introduction
 Discovered by Henry Cavendish and named it as
Inflammable element.
 Lavoisier named it hydrogen
(Hydro= Water Gene=producer)
 Lightest Element in Periodic Table.
 Most Abundant in Universe.
 9th most abundant on Earth’s crust.
 Order of Abundance:
 Universe > Sun > Earth
 Due to more gravitational pull of Sun , atomic form of
hydrogen is available but on Earth it is present in
molecular form.

 It is the simplest element with electronic configuration
of 1s1
having only one proton and one electron (and no
neutrons in its most common isotope).
 Hydrogen is most reactive in atomic form but less
reactive in molecular form because of greater extent of
overlapping of 1s-1s orbitals.
 Hydrogen is the fuel for reactions of the Sun and other
stars (fusion reactions).. All stars are essentially large
masses of hydrogen gas that produce enormous
amounts of energy through the fusion of hydrogen
atoms at their dense cores.
 In smaller stars, hydrogen atoms collided and fused to
form helium and other light elements like nitrogen and
carbon(essential for life).
Introduction

Isotopes of
Hydrogen
Hydrogen (H) has 3 naturally occurring isotopes,
sometimes denoted 1H, 2H, and 3H.
The first two of these are stable, while 3H has
a half-life of 12.32 years.

Isotopic Effect
 The Change in properties of isotopes due to difference in
mass is called Isotopic effect.
 Large change in properties is seen in the isotopes of
hydrogen due to large differences in the mass.
 In other elements the mass difference is not so large so
less changes are seen.
 Hydrogen Isotopes are used in study of reaction rates.
This is also referred as Kinetic Isotopic effect.
Br2 + CH4 → HBr + CH3Br
(Reaction Fast as C-H Bond breaking is involved)
Br2 + CD4 → DBr + CD3Br
(Reaction Slow as C-D Bond breaking is involved)

Why do we have
Unique Position of
Hydrogen

Position In Periodic
Table
 The placement of elements in the periodic
table is based on their electronic
configuration.
 This structure is similar to that of alkali metals
(ns1) which have 1 electron in their outermost
shell.
 It can attain the noble gas configuration of
helium, by accepting one electron. This
character is very much similar to that of
halogen family (ns2 np5) which are also short of
one electron to complete the octet of electrons
in their shells.

 Electronic Configuration : contains one
Electron In the outermost shell.
 Electropositive : Like Alkali metals, Hydrogen also
looses its one electron to form hydrogen ion, i.e., H+
 Combination With Electronegative Elements : Like
Alkali metals Hydrogen also combines with
electronegative elements such as oxygen, sulphur,
halogen.
 Oxidation State : Hydrogen also shows the oxidation
state of +1 in its compound.
 Reducing Character : Like Alkali metals Hydrogen
also act as a strong reducing agent.
Resemblance With Alkali Metals

 Electronic Configuration : All the Halogen wants one
electron to complete its octet, this property is shown
by Hydrogen also.
 Electronegative Character : Halogens have a strong
tendency to gain electron to form halide, Hydrogen also
shows same tendency.
 Ionization Enthalpy : Ionization Enthalpy of Hydrogen is
quite comparable with those of the Halogen.
 Oxidation State : Just Like halogen Hydrogen shows the
oxidation state of -1.
 Combination With Metals : Hydrogen combines with the
metals in the same way as the halogens combine.
Resemblance With Halogen

 Nature Of oxides : Hydrogen forms oxides that
are neutral unlike alkali metals & halogen.
 Size Of ion : The Size of ion is not
comparable with the size of the ions of alkali
metals & halogen.
Differences from Halogen &
Alkali metals

Classification Of
Hydrogen
Based On Reactivity
Atomic Hydrogen Nascent Hydrogen Molecular Hydrogen Adsorbed Hydrogen
Based on Nuclear Spin
Ortho Hydrogen Para Hydrogen

 Lab Preparation :
1. Reaction of dilute acid with
granulated impure zinc
Zn + H2SO4 → ZnSO4 + H2
Preparation Of Hydrogen

 Lab Preparation :
2. Reaction of NaOH with metals
like Pb, Be, Zn , Al and Sn.
Zinc reacts with NaOH to form
sodium zincate with the
evolution of hydrogen gas.
Zn + 2NaOH → Na2ZnO2 + H2

 Commercial Preparation
1. Electrolysis of acidified water/
alkalinated water using platinum
electrodes.
Electrolysis
2H2O (l) → 2 H2 (g) + O2
Water is acidified by adding
some amount of H2SO4
OR
Water is alkalinated by adding
some amount of Ba(OH)2

Commercial Preparation
2.Electrolysis Of Brine solution
Electrolysis
Na+ + Cl - + H2O(l) → 2NaOH +
H2 + Cl2
Cell used for electrolysis:
Nelson Cell
Caster Kellner Cell

3.Lane’s Process: In the steam-iron process
the iron oxidizes and has to be replaced with
fresh metal.
3Fe+ 4H2O → Fe3O4 + 4H2
Lane hydrogen producer the iron
is reduced with water gas back to its metallic
condition, after which the process restarts.
Fe3O4+ 4CO → 3Fe + 4CO2

4. Reaction of steam with Hydrocarbons in the
presence of Catalysts to produce water gas.
If nitrogen is present it forms producer gas
CH4 + H2O → CO + H2
• (Co + H2 ) → Water Gas or Syngas
• (CO + N2) → Producer Gas
Next Step is Water Gas Shift Reaction
CO + H2 + H2O (g) → CO2 + 2H2

 Physical Properties :
i. Colorless
ii. Tasteless
iii. Odorless
iv. Lightest substance.
v. Slightly soluble in water.
vi. Can be liquefied under low
temperature & high pressure.
vii. Low Melting and Boiling Point
Properties Of Dihydrogen

 Chemical Properties :
i. Neutral In nature
ii. Less Reactive in molecular form
iii. Reaction With Metal: formation of
ionic hydrides.
2Na + H2 → 2NaH
iv. Reaction With Oxygen: formation
of Water
2 H2 + O2 → 2 H2O

v. Reaction With Nonmetals
Halogen
H2 + X2 → 2HX(X=F, Cl, Br, I)
Dinitrogen
N2 + 3H2→ 2NH3
Sulphur
H2 + S → H2S
Carbon
C + 2H2 → CH4

vi. Hydrogenation of Veg. Oil
Unsaturated hydrocarbons (Veg. Oil) add
dihydrogen in presence of catalysts (like
Ni, Pt, Pd) to form saturated
hydrocarbons(Veg. Ghee)

 Hydrogenation of Vegetable Oil to solid
fats.
 Manufacturing of chemicals
(methanol,ammonia, hydrocarbons)
 Manufacture Of metal Hydrides .
 In Metallurgy to reduce heavy metals.
 Used as rocket propellent (liquid
hydrogen + liquid oxygen)
 Used in balloons (15% H2 + 85% He)
 Nuclear weapons.
Uses Of
Dihydrogen

Hydrides
 Compounds of hydrogen with other
elements are called hydrides.
 Hydrides are classified in three types
based on bonding present:
A. Ionic or Salt like hydrides
B. Covalent or Molecular
hydrides
C. Metallic or Interstitial
Hydrides

Hydrides in
Periodic Table
 The elements that do not form hydrides are indicated
as hydride gap in periodic table.(Complete Group 7,8,9
and some other transition metals in different groups)

Ionic or Saline
Hydrides
 They are formed when hydrogen molecule
reacts with highly electropositive s-block
elements (Alkali Metals and Alkaline Earth
Metals).
 In solid-state, the ionic hydrides are crystalline,
non-conducting and non-volatile. However, in
a liquid state, they conduct electricity.
 Ionic hydrides on electrolysis liberate
hydrogen gas at the anode.
 Saline or ionic hydrides does not dissolve in
conventional solvents and they are mostly used
as bases or reducing reagents in organic
synthesis.
 Example of Ionic Hydrides: NaH, KH, CaH2
 These contain hydrogen as the negatively
charged (H–) ion

Covalent or Molecular
Hydrides
Covalent hydrides are formed when
hydrogen reacts with other similar
electronegative elements like Si, C, etc.
The most common examples are CH4 and
NH3. In general, compounds that are
formed when hydrogen is reacted with non-
metals are called covalent hydrides.
The compound shares a covalent bond and
are either volatile or non-volatile
compounds.
Covalent hydrides are also either liquids or
gases.
Covalent Hydrides: SiH4 (silane)

Covalent or Molecular
Hydrides

Metallic or Interstitial
Hydrides
 A hydrogen compound that forms a bond
with another metal element is classified as a
metal hydride.
 Metal hydrides are also known as interstitial
hydrides. They are formed when hydrogen
molecule reacts with the d- and f-block
elements.
 The bond is mostly covalent type but
sometimes the hydrides are formed with ionic
bonds.
 These are usually formed by transition metals
and are mostly non-stoichiometric, hard, high
melting and boiling points.
 They do conduct heat and electricity but not
to the extent of their parent metals.
 Example of Metallic Hydrides: TiH1.2-1.8

Metallic or Interstitial
Hydrides

Properties of water
Chemical Formula: H2O
Appearance: Water is colorless, odorless and
tasteless liquid in its natural state.
Boiling Point: 1000C.
Freezing Point: 00C..
Density: One unique property of water is that in the
sold state, it is less dense. Up to 4°C water’s density
does increase on cooling. But after that point water
becomes less dense. This is why ice floats in water,
Viscosity: Water has high viscosity due to very strong
intermolecular interactions
Solvency: Water is an excellent polar solvent. In fact, it
is known as a Universal Solvent.

Properties of water
 Amphoteric Nature: Water is neither acidic or basic it acts as
both. This is because of its ability to both donate and accept
protons. For acids stronger than water it acts as a base. These
two following reactions show this amphoteric nature.
H2O (l) + HCl (aq) ⇌ H3O+ + Cl–
H2O (l) + NH3 (aq) ⇌ NH4
+ + OH–
 Hydrolysis Reaction: Water has a very high dielectric
constant. This results in it having a strong hydrating
tendency. Water has strong reactions with ions of salts and
creates hydrating shells around them.
SiCl4 + 2H2O → SiO2 + 4HCl
 Redox Reactions: Water is a great source to obtain
dihydrogen since it can be reduced by reacting it with highly
electropositive metals such as Sodium.
H2O + Na → 2NaOH + H2

ICE
The structure of the molecules of water in its frozen
form i.e. ice is very unique. It forms a Lattice Structure
that does not generally occur naturally in any other
substance other than ice.
When water reaches its freezing point its atoms
rearrange themselves in a very specific three-
dimensional pattern. The oxygen atom is surrounded
by four hydrogen atoms. Two of these form O-H bonds
normally seen in water molecules. The other two form
a hydrogen bond.
This very special hexagonal shape is what gives ice
the unique property of being less dense than water.
Since in the structure of ice there are empty spaces
between the hexagonal structure, its density is less
than that of water in its liquid state. This is why ice

Hard water
and
Soft water
Water
Hard Water
• Water which do not
produces lather with Soap
Soft Water
• Water which produces
good lather with Soap

Hard water
and
Soft water
Types Of
Hardness
Permanent Hardness
• Contains chlorides/ sulphates
of Calcium/ Magnesium
Temporary Hardness
• Contains bicarbonates of
Calcium/Magnesium

Why softening of
Hard Water is
essential?
Reduction of soap consumption
Lowered cost in the maintenance of
plumbing
Improved taste in foods prepared
A must for industrial supplies
4
RGU IIITNUZVID
Courtesy: lenntech.com
Courtesy: ndsu.edu
basin

Removal of temporary
hardness (Boiling
Method)
Temporary hardness is due to carbonates and
bicarbonates of calcium and magnesium. It Can
be removed either by boiling
• 𝐶𝑎𝐶𝑂3 is slightly soluble in water.
• So it usually exists in water as a bicarbonate.
• Boiling will lead to the precipitation of 𝐶𝑎𝐶𝑂3 and
release of 𝐶𝑂2.
𝐶𝑎(𝐻𝐶𝑂3)2 (On Boiling)→ 𝐶𝑎𝐶𝑂3 (s)+ 𝐶𝑂2 (g) +𝐻2O
Mg(𝐻𝐶𝑂3)2 (On Boiling)→ Mg𝐶𝑂3 (s)+ 𝐶𝑂2 (g) +𝐻2O
• 𝐶𝑎𝐶𝑂3 and MgCO3 is precipitated.

Removal of temporary
hardness (Clark’s
Process)
 In Clark’s method of water softening, hard
water is treated with Ca(OH)2 (slaked lime).
 Water softening by Clarke’s process uses
calcium hydroxide (lime). It removes
temporary hardness.
Ca(HCO3)2+Ca(OH)2→2CaCO3+2H2O.
 This method involves the addition of slaked
lime to water either in solid or in liquid
form.
 This results in the conversion of soluble
bicarbonates to insoluble carbonates.

Removal of Permanent
hardness (Washing
Soda)
 Sodium carbonate, Na2CO3, is also known as washing
soda. It can soften water that has temporary hardness
and it can soften water that has permanent hardness.
 Sodium carbonate is soluble in water and adds a large
amount of carbonate ions to the water. These react with
dissolved calcium and magnesium ions, forming
a precipitate of their carbonates
Ca2+(aq) + CO3
2–(aq) → CaCO3(s)
Mg2+(aq) + CO3
2–(aq) → MgCO3(s)
 The calcium ions come from the hard water and the
carbonate ions from the washing soda.

hardness (Calgon’s
Process)
 Calgon method involves treatment of Calgon
(sodium hexametaphosphate, Na6P6O18) to
form complex anion, which keeps the Mg 2+
and Ca 2+ ions in solution
 Calgon ionizes to give a complex anion:
(NaPO3)6 → 2Na+ + [Na4P6O18 ]2-
 The addition of Calgon to hard water causes
the calcium and magnesium ions of hard
water to displace sodium ions from the anion
of Calgon.
Ca2++ [Na4P6O18 ]2- → 2Na+ +
[CaNa2P6O18 ]2-
 Anion of calgon goes into solution This
results in the removal of calcium and
magnesium ions from hard water in the form
of a complex with Calgon.

hardness (Permutit or
Zeolite Process)
 Zeolites are naturally occurring sodium aluminum silicates
having different amounts of water of crystallization.
 They are represented as Na2O.Al2O3.xSiO2.yH2O where x and
y varies from 2 to 10 and 2 t 6 respectively.
 They are produced synthetically as well.
 They have the property of exchanging their Na ions for
hardness causing ions like Ca++ and Mg++
 The reactions taking place the softening process are as
follows where Ze represents zeolite.
Ca(HCO3)2+Na2Ze→CaZe+2NaHCO3
MgSO4+Na2Ze→MgZe+Na2SO4
CaCl2+Na2Ze→CaZe+2NaCl
 The Ze mineral gets exhausted when all the Na+ are
replaced by Ca++ and Mg++ ions. Now Ze can be
regenerated by passing Nacl solution,
CaZe+2NaCl→CaCl2+Na2Ze

hardness (Permutit or
Zeolite Process)
 Zeolite softening is carried out in large cylindrical tank
as shown, holding Ze material on a perforated
platform.
 The tank has two inlets for feeding raw water and
passing saturated NaCl solution.
 There are two outlets for softened water and
removing CaCl2,MgCl2 the wash water formed during
the regeneration.

hardness (Ion Exchange
Resins)

Resins)
 An ion-exchange resin or ion-exchange polymer is a
resin or polymer that acts as a medium for ion
exchange. It is an insoluble matrix (or support
structure) normally in the form of small (0.25–0.5 mm
radius) microbeads
 The beads are typically porous, providing a large
surface area on and inside them the trapping of ions
occurs along with the accompanying release of other
ions, and thus the process is called ion exchange.
 There are multiple types of ion-exchange resin. Most
commercial resins are made of polystyrene sulfonate.
 Ion-exchange resins are widely used in water softening
and water purification.

Resins)
 In this application, ion-exchange resins are used to
replace the magnesium and calcium ions found in
hard water with sodium ions.
 When the resin is fresh, it contains sodium ions at its
active sites. When in contact with a solution
containing magnesium and calcium ions (but a low
concentration of sodium ions), the magnesium and
calcium ions preferentially migrate out of solution to
the active sites on the resin, being replaced in
solution by sodium ions. This process reaches
equilibrium with a much lower concentration of
magnesium and calcium ions in solution than was
started with.

Resins)
 The resin can be recharged by washing it
with a solution containing a high
concentration of sodium ions (e.g. it has
large amounts of common salt (NaCl)
dissolved in it).
 The calcium and magnesium ions migrate
from the resin, being replaced by sodium
ions from the solution until a new
equilibrium is reached.
 The salt is used to recharge an ion-
exchange resin, which itself is used to
soften the water.

Heavy Water
 Deuterium is a stable isotope of hydrogen
and Heavy Water (D2O) contains two atoms
of Deuterium (D) and one atom of oxygen.
This is also known as Deuterium Oxide.
 Ordinary water as obtained from most
natural sources contains about one
deuterium atom for every 6,760 ordinary
hydrogen atoms and the residual water is
thus enriched in deuterium content

Heavy Water
 Methods of Preparation :
A. Prolonged Electrolysis of water:
On electrolysis of water, the water
disassociates in H+ and OH- while fractional
part disassociates in D+ and OD- ions. Due to
higher mass D+ and OD- have lower mobility
and H2 and O2 releases from water leaving
D2O in solution. Process is repeated 6 times.

Heavy Water
A. By Fractional Distillation
At normal atmospheric pressure the boiling
point of ordinary water and heavy water are
373K and 374.42K.So can be separated by
fractional distillation of water. Generally
fractionating column of 12 meters is used to
isolate heavy water from ordinary water.

Heavy Water
A. By Fractional Distillation

Heavy Water
 Physical Properties:
 Colorless
 Odorless
 Tasteless
 Higher B.P , M.P. is seen due to marked
difference in mass from ordinary water.
 Dielectric constant of heavy water is smaller
than ordinary water therefore ionic
compounds are slightly less soluble in heavy
water.

Heavy Water
 Chemical Properties:
 All chemical properties of heavy water are
same as that of ordinary water only the rate
of reaction is slow as the bond disassociation
is slow and more energy consuming than
ordinary water.

Heavy Water
 Uses:
 In tracer studies for organic reactions
kinetic studies
In tracer studies for biological and metabolic
testing
In atomic/nuclear reactors for slowing the
speed of moving neutrons (as a moderator)
 in temperature control for nuclear reactors
(as a coolant).
 In testing instruments like FTIR and NMR
spectroscopes.

D2O as a
Moderator and Coolant

Hydrogen Peroxide
 HydrogenPeroxide was discovered by a
French chemist J.L. Thenard in 1818.
 Hydrogen peroxide(H2O2 ) has a open book
like structure. H2O2 has a none planar
structure in which two H atoms are arranged
in two directions almost perpendicular to each
other and to the axis joining the two oxygen
atoms.
 The O─O linkage is called peroxide linkage. In
the solid phase, the dihedral angle is reduced
to 90.2 degree from 111.5 degrees in the gas
phase.

Hydrogen Peroxide
A. The action of cold, dil. sulphuric acid on
sodium peroxide. (Merck’s process)
Hydrogen peroxide is prepared by adding
sodium peroxide to ice cold dil. sulphuric acid.
The addition is carried out slowly in small
amounts with stirring. On upon cooling,
crystals of Na2SO4 .10H2O separate out. The
crystals of Na2SO4 .10H2O are decanted
leaving behind solution of hydrogen peroxide
Na2O2+H2SO4→Na2SO4+H2O2

Hydrogen Peroxide
B. The action of cold, dil. sulphuric acid on
barium peroxide.
In this method, a paste of hydrated barium
peroxide is prepared in ice cold water and is
treated with about 20% ice cold solution of
sulphuric acid.
BaO2.8H2O+H2SO4→BaSO4+H2O2+8H2O
The white precipitate of BaSO4 is removed by
filtration leaving behind about 5% solution of
H2O2

Hydrogen Peroxide
C. By the electrolysis of 50% sulphuric acid
In this method, a 50 % solution of sulphuric
acid is electrolyzed at high current d in an
electrolytic cell when peroxodisulphuric
acid is formed at the anode. The acid is drawn
off from the cell and hydrolyzed with water
to give H2O2 .
2H2SO4→H2S2O8+H2
H2S2O8 + 2H2O → H2O2 + 2H2SO4

Hydrogen Peroxide
D. By 2-ethyl anthraquinone
The method involves the following steps:
i. 2 ethyl anthraquinone is dissolved in
benzene and hydrogen gas is passed in
the presence of palladium catalyst.
ii. The reduced product is dissolved in a
mixture of benzene and cyclohexanol
and upon passing air, it is oxidised back
to 2 ethyl anthraquinone and H2O2 is
produced.

Hydrogen Peroxide
D. By 2-ethyl anthraquinone

Hydrogen Peroxide
 Physical Properties:
 Pure H2O2 is a thick syrupy liquid which
is colorless, odorless and bitter in taste.
 It is more viscous, less volatile and dense
than water.
 Extent of H-Bonds more so higher B.P.
 It is a dibasic weak acid.
 Its melting point is 272.4K and boiling
point is 358K at 68mm of Hg pressure.
 It is completely miscible with water,
alcohol and ether in all proportions.
 30% aqueous solution is called
PERHYDROL.

Hydrogen Peroxide
H2O2 behaves as an oxidizing agent as
well as reducing agent in both acidic
and alkaline solution.
Oxidizing action in acidic medium
In the presence of an acid, H2O2 can
accept electrons and, thus acts as an
oxidizing agent. `
2Fe+2H++H2O2→2Fe+2H2O2
 Reducing action in acidic medium
HOCl+H2O2→H3O++Cl-+O2

Hydrogen Peroxide
 Oxidising action in basic
medium
2Fe+H2O2→2Fe+2OH-
 Reducing action in basic medium
I2+H2O2+ 2OH- →2I-+ 2H2O+O2

Hydrogen Peroxide
 Uses:
 It is used in industry as a bleaching
agent for textiles, paper, pulp,
straw, leather, oils, fats etc.
 It is used as an antiseptic for
washing wounds, teeth and ears
under the name perhydrol.
 It is used as a mild disinfectant and
a hair bleach.
 It is used in preparation of high
quality detergents like perborates
and percarbonates.
 It is used for restoring the color of
lead paintings.

Hydrogen Peroxide
 It is used for the production of
epoxides and polymers.
 It is used for the synthesis of
hydroquinone, pharmaceuticals,
food products.
 It is used as an antichlor in bleaching
also for for preserving milk and
wines.
 It is also used in environmental
chemistry such as in pollution
control treatment of domestic and
industrial effluents, oxidation of
cyanides and restoration of aerobic
conditions to sewage waste.

Storage of H2O2
 The following precautions must be taken
while storing H2O2 :
 It must be kept in wax lined bottles
because the rough glass surface causes
its decomposition. It can also undergo
photodecomposition so colored bottles
used.
 A small amount of phosphoric acid,
glycerol or acetanilide is generally added
which retard the decomposition of H2O2 .
These are also called negative catalysts.

Hydrogen and its compounds

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