A Few Basic Things to know about 

HYDROGEN

1. Hydrogen is the first element of the periodic table 

2. In element form ,it exists as H₂ and is called Dihydrogen

3. IT FORMS MORE COMPOUNDS THAN ANY OTHER ELEMENT

Its position in the modern periodic table has been a topic of discussion in the past because it shows similarities with IA group of elements and also with VIIA group of elements 

Like Alkali metals , it forms oxides , sulphides and halides. 

But unlike Alkali metals it has a very high ionization energy and does not possess metallic characteristics under normal conditions. 

However , in terms of reactivity , is very low as compared to halogens.

1. Electronic configuration - ns1

2. It forms H⁺ ions 

3. High affinity for non metals 

1. Easily Forms H^- ions 

2. Small atomic size

3. 1 electron less than noble gas configuration 

4. I.P values of H₂ comparable to VII A group 

• H = 13.6eV 
• Cl = 13eV
• F = 17eV  

1. Most abundant element in the universe 

2. 70 % of the total mass of the universe 

3. Terrestrial Hydrogen carrying 0.0156% of Heavy Hydrogen in the form of HD.

4. Based on no. of atoms , it is the second most abundant element in the earth's crust. 

5. It is the 10th most abundant element on earth by mass.

1. Hydrogen has three isotopes : Protium , Dueterium and Tritium.

2. In all the isotopes , no. of electrons = no. of protons = 1 

3. The difference in the isotopes is in the number of protons. Protium , deuterium and tritium have 0 , 1 and 2 protons, respectively.

4. Abundance of Protium , Dueterium and Tritium are 99.984% , 0.0156% and 7 * 10^-19%

1. Since the isotopes have the same no. of electrons , they do not differ much in their chemical properties.

2. They only differ in their rate of reactions mainly due to their different enthalpy in bond dissociation.

3. These isotopes differ considerably a lot in their physical properties due to the difference in the no. of neutrons or difference in their mass numbers.

For 

• Mass 
• Density 
• Specific Heat
• Latent Heat of Vaporization 
• Latent Heat of Fusion 
• Boiling point 
• Bond Energy 
• Delta HF ( Heat Of Formation ) 

Protium < Deuterium < Tritium 

Order Of Stability is 

Protium > Dueterium > Tritium

Order of Adsorption of the surface is 

Protium > Dueterium 

Because Activation energy of Protium is greater than that of Dueterium.

Natural Formation 

N_{7^{14 + neutron (} 0}n¹ ) → C₆¹² + H₁³

Artificial Formation 

Li₃⁶ + neutron (₀n¹ ) → He₂⁴ + H₁³

1. Among the isotopes of Hydrogen , it is the only one which is radioactive.

2. It is the lightest radioactive isotope in the periodic table.

3. It is a soft Beta particle emitter.

H₁³ → He₂³ + β

4. Half life of tritium is 12.3 years.

5. Not a harmful isotope.

1. Ortho and Para Hydrogen 

2. Nascent Hydrogen 

3. Atomic Hydrogen 

4. Occluded or Adsorbed Hydrogen 

1. Hydrogen gas carries two types of molecules , they are nothing but ortho molecules and para molecules .

2. Ortho and Para Hydrogen differ in their nuclear spins or plutonic spins , thus they are known as NUCLEAR SPIN ISOMERS.

The Hydrogen molecules in which the spin of the atomic nuclei of both the atoms of Hydrogen are identical i.e., clockwise is called Ortho Hydrogen.

Ortho Hydrogen is said to be in triplet state.

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The hydrogen molecules in which the spin of the atomic nuclei of the hydrogen atoms are opposite , i.e., if one is clockwise then the other is anti-clockwise is termed as Para Hydrogen.

Para Hydrogen is in Singlet State , unlike Ortho Hydrogen which is in Triplet State.

[image]

Ortho and Para Hydrogen differ in some of their physical properties like : 

1. Internal Energies

2. Thermal Conductivity 

3. Specific Heats 

4. Boiling Points 

5. Band Spectra 

Ortho and Para Hydrogen can be separated by : 

1. Charcoal Method 

2. Gas Chromatography 

1. In simple words it is baby oxygen or you can say just born Hydrogen.

2. Nascent Hydrogen is MORE reactive than normal Hydrogen .

PREPARATION OF NASCENT HYDROGEN :

• Zn + H₂SO₄ → ZnSO₄ + 2[H] 
• Zn +  2HCl → ZnCl₂ + 2[H]
• Na + C₂H₅OH → C₂H₅ONa + [H]

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  3. KMnO₄ + H₂SO₄ → NO REACTION and no decolorization of KMnO₄

But KMnO₄ + H₂SO₄ + Zn → ZnSO₄ + 2[H] and  decolorization of KMnO₄  takes place

4. The activity of nascent Hydrogen depends upon the source from which it is generated .

1. Preparation of Atomic Hydrogen : When H₂ gas is passed through an electric orb between two tungsten electrodes , the molecules of H₂ split into Hydrogen atoms known as Atomic Hydrogen.

2. The lifespan of atomic hydrogen is very small , so it recombines quickly to form Hydrogen gas , thus releasing a lot of heat energy . This heat energy is used for welding . This type of welding is called Hydrogen Welding.

1. When H₂ gas is passed over finely powdered heavy metals like Iron , Cobalt , Nickel , Platinum and Iridium - H₂ gas get adsorbed in the interparticle spaces. Such H₂ is called Occluded or Adsorbed H₂.

2. Large amounts of Hydrogen , i.e., around 500 - 800 volumes of H₂ gets adsorbed into one volume of powdered metal. This adsorbed H₂ is used for 

• Storage Purpose 
• Synthetic purpose 
• Reduction Purpose 
• Ultrapurification of H₂

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1. ELECTROLYSIS OF ACIDIFIED OR ALKALINE WATER

2H₂O (electrolysis)→2H₂+O₂ 

2. METALS WITH STEAM

3Fe + 4H₂O  → Fe₃O₄ + 4H₂

(Red hot)                                    

Zn + H₂O → ZnO + H₂ 

(Red Hot)                                 

                         3. LABAROATORY PREPARATION - REACTION WITH ACIDS

Zn + 2HCl → ZnCl₂ + H₂

Fe + H₂SO₄ → FeSO₄ + H₂

4. LABORATORY PREPARATION - REACTION WITH ALKALI           

2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

                           _{( Sodium Meta Aluminate)}

Zn + 2NaOH → Na₂ZnO₂+ H₂

                _{(Sodium Zincate )}

This is very very important as it is of crucial importance in electrochemical chemistry !

Li 

K 

Ba

Sr

Ca

Na

Mg

Al

Mn

Zn

Cr

Fe

Cd

Ni

Sn

Pb

H

Cu

I

Ag

Hg

Bi

Pt

O

Cl

Au

F

1. Electrolysis of Acidified or Alkaline Water :

2H₂O → 2H₂+O₂

2. Lane's Process :

3Fe + 4H₂O → Fe₃O₄ + 4H₂

_{Red Hot     Steam}                               

_{NOTE : Electrolysis method and Lane's process is used for both general and commercial methods of Hydrogen !}

3. Hydrolysis of Hydrolith :

Hydrolith = CaH₂

CaH₂ + 2H₂O → Ca(OH)₂ +2H₂

4. Nelson Cell Process : 

• Electrolysis Of NaCl : NaCl → Na⁺ + Cl^-
• At anode : 2Cl^- → Cl₂ + 2 e^- 
• Electrolysis of NaOH  ← Na⁺ + OH^-
• At anode : 2H₂O + 2e^- → 2OH^- + H₂

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  ^{Note : Nelson's Cell Process is actually meant for commercial preparation of NaOH. But simultaneously , a large amount of H₂ and Cl₂ gas is also released.}

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  5. From Hydrocarbons :

CH₄ + H₂O → CO + 3H₂

6. Petroleum Industry :

The best commercial / industrial source of Hydrogen is the petroleum industry which accounts for 77% of the Hydrogen gas produced.

The second best source is Coal Gasification which produces 18% of the Hydrogen for our need.

7. BOSCH's Process or Coal Gasification :

• Step 1 : Coal Gasification 

C + H₂O → CO + H₂

Red Hot    Steam     Water gas

• Water gas is now treated with double the amount of steam as before 
• Step 2 : Water Gas Shift Reaction 

CO + H₂ + H₂O → CO₂ 2H₂ 

• Now , the mixture obtained is passed through KOH. KOH absorbs CO₂ and leaves behind H₂
• Step 3 : Passing through KOH

CO₂+2H₂ → 2H₂ ( In presence of KOH soln. , -CO₂)

1. Electrolysis of Ba(OH)₂ using Pt/Ni electrodes : 

At cathode : Pure Hydrogen gas is evolved 

At anode : Oxygen gas is evolved

2. Hydrolysis of NaH : 

NaH + H₂O → NaOH + H₂

3. Uyeno's Method :

Scrap Aluminium treated with Dilute Alkali

2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

_{(Scrap )}                                                             

NOTE : Uyeno's method of preparation of Hydrogen is generally used for military purposes .

The various impurities present in Hydrogen gas include : 

1. Phosphine (PH₃)

2. Arsine (AsH₃)

3. Hydrogen Sulphide (H₂S)

4. Carbon dioxide (CO₂)

5. Sulphur Dioxide (SO₂)

1. To remove AsH₃ and PH₃ → Add AgNO₃

2. To remove H₂S → Add ??

3. To remove CO₂ and SO₂ → Add KOH 

4.Water and Hydrogen is left → Add P₄O₁₀ or concentrated H₂SO₄ to remove H₂ gas , Pure and dry H₂ is left.

1. Colorless , odorless , tasteless 

2. Very less soluble in water or almost insoluble

3.Combutible in presence of O₂

4. The important property of Hydrogen is of occlusion/adsorption which is discussed under occluded or adsorbed Hydrogen in detail so please refer that also and learn it .

1. COMBUSTION :

Hydrogen is combustible only in the presence of Oxygen. It burns with a blue flame to give H₂O. It is a highly exothermic reaction.

2H₂+O₂→2H₂O (delta HF = -284kJ/mole)

2. REACTION WITH HALOGENS : 

The reactivity of Hydrogen with the halides decreases from top to bottom.

H₂+F₂→2HF (dark conditions)

H₂+Cl₂→2HCl(sunlight)

H₂+Br₂→2HBr(570⁰C)

H₂+I₂→2HI(570⁰C + Pt catalyst)

3. REDUCING PROPERTY 

H₂ is a strong reducing agent . It reduces metal oxides to metal.

CuO + H₂ → Cu + H₂O 

AgCl +H₂ → Ag + HCl

4.OXOPROCESS or HYDROFORMYLATION :

Hydrogen in the presence of CO reacts with alkanes to produce aldehyde with increase in carbon chain by one unit. This aldehyde , further on reduction with H₂ gas produces a long chain alcohol. This entire process is known as an OXOPROCESS.

H₂ + CO + R-CH=CH₂ → R-CH₂-CH₂-CHO (again +H2) →R-CH₂-CH₂-CH₂-OH

H₂ reacts with almost all elements to produce binary compounds called Hydrides.

The different types of Hydrides are :

1. Ionic Halides or Salt Hydrides or Saline Hydrides

2.Molecular Hydrides or Covalent Hydrides

3. Interstitial Hydrides

4. Polymeric Hydrides 

5. Complexes

Highly electropositive metals like IA (except Li ) and IIA   ( except Be and Mg ) groups produce ionic hydrides.

IA (Ionic Hydrides)

NaH

KH

RbH

CsH

IIA (Ionic Hydrides)

CaH₂

SrH₂

BaH₂

LiH₂ and BeH₂ - Covalent  Hydrides

MgH₂ - Mixed Hydride (because it has 50% ionic character and 50% covalent character)

Most of the p-block elements like IIIA , IVA , VA , VIA and VII A group of elements from covalent hydrides.

 Types of covalent hydrides :

1. Electron deficient hydrides

2. Electron precise hydrides 

3. Electron Rich Hydrides

III A group of elements like Al and B form Electron deficient halides 

They have a sextet configuration and can easily accept electrons , therefore , acting as Lewis Acids.

Ex: BH₃,AlH₃

IV A group of elements form electron precise hydrides. These hydrides have a fulfilled octet configuration.

Ex: CH₄,SiH₄etc.

Elements of V A , VI A and VII A form electron rich hydrides.

Group V A ex : NH₃,PH₃

Group VI A ex : H₂O,SO₂

Group VII A ex : HF , HCl

In all of these compounds, the central atom has one or more lone pair of electrons.

Group V A and Group VI A hydrides can donate their electrons and hence act as Lewis Bases.

Group VII A hydrides though has electrons to donate , does not act as a Lewis Base because of high electronegativity of halides and thus they act as Lewis Acids.

These hydrides are formed by transitional and inner transitional elements.

When H₂ is passed over heated transition metals, H₂ occupies the interparticle spaces in between them and form Interstitial Hydrides.

VH , NiH , PdH , CdH₂ , YH₂ are some interstitial hydrides. 

These hydrides resemble the parent metal and therefore , these hydrides are also called METALLIC HYDRIDES.

These are non-stoichiometric compounds.

They are used for 

1.Storage purposes 

2. Synthetic purposes

3. Reduction purposes

4. Ultrapurification of H₂

Be , Al and Si form Polymeric Hydrides. The elements having electronegativities between 1.4 to 2 form such hydrides.

(BeH₂)_n:

Plane perpendicular Structure[image]

(AlH₃)_n:

[image]

In this compound, each Al is surrounded by 6 H atoms by octahedral geometry.

The Hydrogen Bridge bond in both BeH₂ and AlH₃ is an electron deficient bond.

Both of them are 3C-2e^- bonds !

Elements like Boron , Aluminium and Gallium form complex hydrides.

In these hydrides , H atom acts as H^- atom.

H^- is a good ligand (electron pair donor )

In complex hydrides, a simple cation and a complex anion is present.

Examples

1. Li[AlH₄]

2.Na[BH₄]

3.Na[GaH₄]

1. Used in the manufacture of NH₃, HCl and CH₃OH (methyl alcohol).

CO(g) + 2H₂(g)→ CH₃OH(l)

2. H₂ in its occluded or adsorbed form along with Raney-Ni is used for the manufacture of Vanaspati Ghee or Dalda or Margarine.

3. Used in the manufacture of synthetic petrol.

4. H₂ can be directly used as a reducing agent in metallurgy to reduce metal oxides and metal halides to their respective metals.

WCl₆ + 3H₂ → (UV , sunlight) W + 6HCl

MoO₃ + 3H₂ →( supply heat) Mo + 3H₂O 

5. Used in Hydrogen Economy 

The transport of Hydrogen in its liquid or in its gaseous form and not in the form of electrical energy is called Hydrogen Economy.

6.Used in Oxy-Hydrogen Welding which can produce temperatures up to 2800⁰C.

7.Used In H₂ Fuel Cells

A fuel cell is a device which converts the combustion energy of CO , H₂ and CH₄ into electrical energy without burning.

Hydrogen Fuel Cells contain porous carbon electrodes impregnated with metal catalysts.

There can be two types of electrolytes used :

Aqueous KOH solution 

Molten Na₂CO₃ solution

Case 1 : If Aq. KOH solution is used

At Anode : H₂+2OH^-→2H₂O + 2e^-

At Cathode : 1/2 O₂ + H₂O + 2e^-  → 2OH^-

Net Reaction : H₂+1/2 O₂ → H₂O

Case 2 : If Mol. Na₂CO₃ is used 

At Anode : H₂ + CO₃^-2→ H₂O +CO₂  + 2e^-

At Cathode : 1/2 O₂ + CO₂ +2e^- → CO₃^-2

Net Reaction : H₂+1/2 O₂ → H₂O 

1. H₂ gas is an environmentally clean gas ,i.e. on combustion it gives H₂O and not any other impurity.

( Hydrogen may contain Nitrogen as an impurity which on combustion gives NO and NO₂ but it is in very small amount ).

2. The combustion energy of 1 gram of Hydrogen is more than most fuels.

3. The IP value of Hydrogen is high.

4. It is a light gas.

1. The boiling point of Hydrogen is -253⁰C . It  is very expensive.

2. A compressed H₂ gas cylinder exerts a lot of pressure so special alloys are required to make such cylinders  which withstand the high pressure exerted by hydrogen.

Alloys like Na-Ni , Ti-TiH₂ , Mg-MgH₂ need to be used which are expensive.

3. A compressed H₂ gas cylinder weighs 30 times more than a petrol tank , which gives the same amount of energy.

Hydrogen gas is generally transported in the form of Hydrolith (CaH₂) or dry Ammonia (NH₃)

But why ?

1. Hydrolith can be easily undergo hydrolysis to give a large amount of H₂ gas.

2. Dry ammonia easily decomposes under normal conditions to give H₂.

A  FEW  FACTS  ABOUT  WATER 

[image]

1. It is essential for life. 

Human body is 65% water while some plants can contain upto 95% water in them.

2. It is a colorless, tasteless and odorless liquid.

3. Due to the presence of strong hydrogen bonds, it has a high melting , high boiling point, high freezing point, high latent heat of fusion, high latent heat of vaporization compared to H₂S or H₂Se.

4. Rainwater is the purest form of water.

5. Most of the compounds carry water molecules, known as Water of Crystallization and the entire compound is known as a Hydrated Compound.

1. CO-ORDINATED HYDRATES:

Example : [Cr(H₂O)₆]⁺³

In these compounds, water molecules are bonded to the central atom by covalent bonds. Therefore, these compounds are called Co-ordinated Hydrates.

2. INTERSTITIAL HYDRATES :

Example : BaCl₂.2H₂O (This is always dihydrate)

In these compounds, water molecules occupy interparticle spaces between the atoms of central element. Therefore, these compounds are called Interstitial Hydrates.

3. CO-ORDINATED AND HYDROGEN BONDED HYDRATES:

Example : CuSO₄.5H₂O

In the above molecule, 4 water molecules are bonded to Cu⁺² by co ordinate covalent bonds. 

One water molecule is bonded to the compound by covalent bond.

In these type of compounds, we can observe all types of bonding like 

1. Covalent bonding 

2.Co ordinate covalent bonding 

3. Ionic Bonding 

4. Hydrogen bonding  

1.SOFT WATER:

Water which forms lather with soap easily.

2.HARD WATER:

Water which does not form lather with soap.

The hardness of water is due to the presence of bicarbonates , chlorides and sulphates of Calcium and Magnesium.

2C₁₇C₃₅COONa +Ca⁺²or Mg⁺²→ (C₁₇H₃₅COO)₂Ca/Mg

↓                                                   

Soap or sodium salt of stearic acid

1.TEMPOARARY HARDNESS:

This is due to presence of bicarbonates of Ca and Mg.

2. PERMANENT HARDNESS:

This is due to presence of chlorides and sulphates of Ca and Mg.

1.BOILING :

Mg(HCO₃)₂ → Mg(OH)₂ + CO₂

Ca(HCO₃)₂ → CaCO₃ + CO₂ + H₂O

These precipitates can be separated by filtration. As a result, hard water changes to soft water.

2. CLARK'S PROCESS :

(Industrial method)

In this process, required amount of Slaked Lime[Ca(OH)₂] or Lime[CaO] is added and heated.

Mg(HCO₃)₂  + Ca(OH)₂→ Mg(OH)₂ + CaCO₃ + H₂O +CO₂

Ca(HCO₃)₂ + Ca(OH)₂→ CaCO₃ + H₂O +CO₂

3. ADDITION OF COMPLEXING OR CHELATING AGENTS:

Poly Amino acids/ Poly Phosphates (EDTA - Ethylene Diamine Tetra Acetate) is added to Hard water.

Ca/Mg thus form soluble complexes and thus, their activity is suppressed. Therefore, hard water gets converted into soft water.

NOTE:

SEQUESTATION:

 The suppression of the activity of Ca⁺² and Mg⁺² in hard water by the addition of complexing or chelating agents is known as sequestation.

This method is also applied in boilers.