Chemistry

Hydrogen

Session opener

What do you understand by word “Hydrogen” ?

Hydrogen in Greek meansWater 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

• In modern periodic table it is located in first group.

Alkali metals Halogens

• lightest element known having atomic number 1.

• Dihydrogen

• The position of hydrogen is anomalous in periodic table

Resemblance with alkali metals

1. Electronic configuration

11

2 2 6 111

2 2 6 2 6 119

H 1s

Na 1s , 2s , 2p , 3s

K 1s , 2s , 2p , 3s , 3p , 4s

H+, Na+, K+ etc.

3. Oxidation state: +1

2. Electropositive character

Resemblance with halogens

Both contain one electron less than the nearest noble gas configuration

11 2

2 2 59 8

2 2 6 2 517 18

H 1s near to He

F 1s , 2s , 2p near to Ne

Cl 1s , 2s , 2p , 3s , 3p near to Ar

Typical non-metals.

Diatomic molecules.

1. Electronic configuration:

2. Non-metallic character:

3. Atomicity:

4. Formation of similar types of compounds

i. Halides: CCl4, SiCl4, GeCl4

ii. Hydrides: CH4, SiH4, GeH4

5. Oxidation state: –1

1 1 1 1Na H Na Cl

Isotopes of hydrogen

Methods for commercial production of dihydrogen

–

electrolysis

2 2 2H / OH2H O 2H O

2. By partial oxidation of hydrocarbons

1. Electrolysis of water

2 3

673 K2 2 2

Fe OCO H O CO H

Methods for commercial production of dihydrogen

2 3

673 K2 2 2

Fe OCO H O CO H

3. Water gas shift reaction

By Lane process

1025 - 1075 K2 (g)3Fe 4H O 3 4 2Fe O 4H

(2) Reduction stage

3 4 2 2 2

water gas

Fe O 2H CO 3Fe 2H O CO

(1) Oxidation stage

Bosch process

2 3 2 3

2

Fe O / Cr O

steam, 770 KCO H

Cold water

2 2 underpressure

Re d hot coke steam water gas

CO H

CO2 dissolves + H2 is collected

1270 K2 (g) 2

Water gas

C H O CO H

2 3 2 3Fe O / Cr O

2 2 2 2770 K

SteamWater gas

CO H H O CO 2H

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 purezinc in the preparation of dihydrogen?

2 4 4 2Zn dil. H SO ZnSO H

(a) Conc. H2SO4 cannot be used because it acts as oxidizing agent also and gets reduced to SO2.

2 4 4 2 2Zn 2H SO (conc.) ZnSO 2H O SO (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)

673 K, 200 atm

Fe3H2 (g) + N2 (g) 2NH3 (g)

(ii) Reaction with nitrogen

(iii) Reaction with oxygen

970 K2(g) 2(g) 2 (g)2H O 2H O

Chemical properties

Reactive metals like Na, K, Ca, Li

525 K2 2Ca H CaH

Metals like Pt, Pd, Ni form interstitial hydrides by absorbing large volume of hydrogen. Such hydrogen is called ‘occluded hydrogen’

(iv) Reaction with metals

Hydrogen reduces oxides of less active metals to corresponding metal

Δ3 4 2 2Fe O + 4H 3Fe + 4H O

2 2CuO H Cu H O

(v) Reaction with metal oxides:-

Ortho and para hydrogens

At room temp.

75% 25%

stability more stable less stable

•Different physical properties

•Similar chemical properties.

Ortho hydrogen Para hydrogen

Atomic hydrogen3270 K

2(g) (g)Atomic hydrogen

H 2H H 435.9 kJ

• Highly reactive.

• Half life period is 0.3 sec.

• 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.

Nascent hydrogen

Structure of water

O

H H104.5°

95.7 pm

O

H H H

HH H H

O O

Gaseous state

Solid state

Structure of iceH

O

H H

H

H

H

H

H

H

H

H

H

O

O

OO

H

H

O

O

O

H

O

Vacant space

H

H

H

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 is free from bicarbonates, sulphates and chlorides of calcium and magnisum. It produce lather with soap solution easily.

Soft water

e.g., distilled water, rain water

Types of hardness

• due to presence of soluble bicarbonates of calcium and magnesium.

• can be removed by simple boiling.

The hardness of water is of two types

(i)Temporary hardness

• due to presence of chlorides and sulphates of calcium and magnesium.

• requires treatment of water to remove this type hardness.

(ii)Permanent 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.

3 3 2 22inso lub leSo lub le

(i) M HCO MCO H O CO (M = Ca or Mg)

Removal of temporary hardness:-

Clark’s method or calcium hydroxide method

3 2 3 22insolubleSoluble

Ca HCO Ca(OH) 2CaCO 2H O

3 2 3 222insoluble insolubleSoluble

Mg HCO 2Ca(OH) 2CaCO Mg OH 2H

Removal of permanent hardness

2 2 3 3

insolubleCaCl Na CO CaCO 2NaCl

4 2 3 3 2 4

insolubleMgSO Na CO MgCO Na SO

(i) By washing soda (Na2CO3.10H2O) treatment

Removal of permanent hardness

ii)By using inorganic cation exchanger (permutit method or Zeolite method):

2 2 2 8 2 2 2 8 2Zeolite settles atbottom

Na Al Si O CaCl Ca Al Si O 2NaCl

The zeolite can be regenerated by treatment with sodium chloride solution.

2 2 8 2 2 2 8 22Ca Al Si O 2NaCl Na Al Si O CaCl

Removal of permanent hardness

(iii) By organic ion exchanger:

2

2In hard water Cation exchanger

Mg 2H re sin Mg (resin) 2H

2

2Hard water Cation exchanger

Ca 2H re sin Ca (resin) 2H

Cation exchanger

Anion exchanger

2

4 4 2Anion exchangerHard water

SO 2HO resin SO resin 2OH

Hard water Anion exchangerCl HO resin Cl re sin OH

22 Re generated resinExchausted resin

Ca resin 2HCl 2H re sin CaCl

Exchausted resin Re generated resinCl re sin NaOH HO re sin NaCl

Hydrogen peroxide

2 2 2 4 2 4 2 2

20% ice cooled 30% solutionsolution

1. Na O H SO Na SO H O

2. From Barium peroxide

2 2 2 4 4 2 2 2BaO .8H O H SO BaSO 8H O H O

Barium sulphate is filtered off leaving behind H2O2.

Methods of preparation

3. By electrolysis of 50% H2SO4

electrolysisH2SO4

4H HSO

At cathode 22H 2e H

At Anode 4 2 2 8Peroxydisulphuric acid

2HSO H S O 2e

distilled2 2 8 2 2 2 2 4

at reduced pressureH S O 2H O H O 2H SO

H2O2 distills first leaving behind the H2SO4 which is recycled.

4. By auto oxidation of 2-ethylanthraquinol

The H2O2 obtained by this method is further concentrated by distillation under reduced pressure.

OH

OH

C2H5

2-ethyl anthraquinol

O

O

C2H5

2-ethyl anthraquinone

air (O2)

Oxidising properties

4 2 4 2 2 2 4 3 2(i) 2FeSO H SO H O Fe (SO ) 2H O

2 3 2 2 2 4 2(ii) H SO H O H SO H O

2 2 4 2Black White

(iii) PbS 4H O PbSO 4H O

Oxidising properties

4 6 2 4 2 2(iv) 2K Fe(CN) H SO H O

6 6 2 2 6 5 2Phenol

(v) C H H O C H OH H

2 2 2 3 2(vii) NaNO H O NaNO H O

2 2 7 2 4 2 2 2 4 5 2(viii) K Cr O H SO 4H O K SO CrO 5H O

3 6 2 2 42K Fe(CN) 2H O K SO

Reducing properties

2 2 3 2 2(i) H O O H O O

2 2 2 2 2 2(ii) Ag O H O 2Ag H O O

2 3 2 2 3 2 2 2(iii) PbO 2HNO H O Pb(NO ) 2H O O

Reducing properties

4 2 4 2 2(iv) 2KMnO 3H SO 5H O

2 2 2 2(v) Cl H O 2HCl O

4 2 2 2(vi) 6KAuCl 3H O 2Au 2KCl 6HCl 3O

2 4 4 2 2K SO 2MnSO 8H O 5O

Acidic properties

It reacts with alkalies and decomposes carbonates.

2 2 2 2 2H O 2NaOH Na O 2H O

2 2 2 3 2 2 2 2H O Na CO Na O H O CO

1. For bleaching silk, wool, hair and leather

2. As rocket fuel

3. Dilute solution is sold in name ‘perhydrol’

Uses of hydrogen peroxide

Do you know?

H2O2 is stored in the bottles lined with wax because…

The rough glass surface causes the decompositionof 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.

2 2 2 22H O 2H O O

2(2 + 32) gm 22.4L at N.T.P.

= 68 gm or 22400 cm3 at N.T.P.

2 2 222400 ml of O is liberated from = 68 gm of H O

Solution

2

2 2

10 ml of O is liberated from=

6810 gm of H O

22400

But 10 ml of O2 at N.T.P. are produced from 1 ml of 10 volume H2O2 solution.

2 2

2 2

1 ml of 10 volume H O solution contains =

6810 gm of H O

22400

= 0.03035 gm

2 2100 ml of 10 volume H O solution contains

= 0.03035 × 100

= 3.035 gm

= 3.035%

Volume strength of hydrogen peroxide (solved example 2)

2 2 22H O 2H O O

Calculate the normality of 30 volume of H2O solution:

2(2 + 32) gm 22.4L

= 68 gm

22.4 L of O2 is produced from = 68 gm of H2O2

2 30 L of O is produced from =

2 2Strength of 20 volume H O solution = 91.07 gm/mL

2 2 2 22H O 2H O O 68 parts by weight 32 parts by weight

Solution

32 parts by weight of oxygen is obtained from = 68 parts by weight of H2O2

2 2

32 parts by weight of oxygen is obtained from =

6868 parts by weight of H O 8 17

32

2 2Equivalent weight of H O = 17

Strength 91.07Normality 5.35

Equivalent weight 17

Structure of hydrogen peroxide

H

95.0 pm

147.5 pm90.2°

101.9°

H

H

95.8 pm

147.8 pm90.2°

101.9°

H

Gas phase Solid phase

Structure of hydrogen peroxide

Illustrative exampleCalculate the normality of 30 volume of H2O solution:

Solution:

2 2 22H O 2H O O

2(2 + 32) gm 22.4 L= 68 gm

22.4 L of O2 is produced from = 68 gm of H2O2

6830 gm

22.4

= 91.07 gm/mLStrength of 20 volume H2O2 solution

2 30 L of O is produced from

solution

2 2 2 22H O 2H O O

68 parts by weight 32 parts by weight

32 parts by weight of oxygen is obtained from = 68 parts by weight of H2O2

parts by weight of oxygen is obtained from = 68

8 1732

Strength 91.07Normality 5.35

Equivalent weight 17

2 2Equivalent weight of H O = 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

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.

Transportation:

Hydrogen gas is explosive and hence it is difficult to store and transport.

Formation of hydrogen from H2O:

Thank you