Hydrogen Class 11th Notes - Free NCERT Class 11 Chemistry Chapter 9 Notes - Download PDF

NCERT Class 11 Chemistry Chapter 9 Notes

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 1

Position of Hydrogen in The Periodic Table

Hydrogen is found on Earth in the form of the H₂ molecule (dihydrogen). It accounts for 10% of the universe's mass. Many compounds, such as carbohydrates and hydrocarbons, release hydrogen. It is the third most abundant element on the planet.

Hydrogen has similarities with alkali metals and halogens.

Similarities with alkali metals

• The number of valence electrons is 1

• Electropositive character

• Oxidation state =+1

• Powerful reducing agent.

Similarities with halogens

• The ionization energy of hydrogen is remarkably similar to that of halogens.

• Hydrogen and halogens exist as diatomic.

• Covalent nature exists in many hydrogen and halogen compounds.

Despite the fact that hydrogen shares some similarities with alkali metals and halogens, it is different from them too. As a result, it has an unique behaviour and placed separately in the periodic table.

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 2

Dihydrogen

Occurrence

Dihydrogen is the most abundant element in the universe(70%). It can be found in a variety of forms, including water, coal, animal, and vegetable materials. Hydrogen is an important component of all organic molecules.

Isotopes

Hydrogen has three isotopes

1. Protium ₁H¹

1 electron, 1 proton and no neutrons

2. Deuterium ₁H²

1 electron, 1 proton and 1 neutron

3. Tritium ₁H³

1 electron, 1 proton and 2 neutrons. It is radioactive.

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 3

Preparation of Dihydrogen

• Laboratory preparation

It is made in laboratories by mixing powdered zinc with dilute hydrochloric acid.

Zn + 2H⁺ → Zn²⁺ + H₂

Zn+2 NaOH → Na₂ZnO₂+H₂

• Electrolysis of water using platinum electrodes

2H₂O Electrolysis→ 2H₂+O₂

• Electrolysis of warm aqueous barium hydroxide solution between nickel electrodes.

• Electrolysis of brine solution

At anode: 2Cl^- → Cl₂+2e^-

At cathode: 2H₂O + 2e^- → H₂ + 2OH^-

• Reaction of steam on hydrocarbons

C_nH_2n⁺¹ + nH₂O Ni,1270 Kn →CO+(2n+1)H₂

Mixture of CO and H₂ is called water gas or syngas. Production of sync gas from coal is called coal gasification.

C+H₂ONi,1270 →KCO+H₂

Water gas shift reaction

CO+H₂O 673 K,Iron chromate→ CO₂+H₂

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 4

Properties of Dihydrogen

Physical properties

• Dihydrogen is a gas that is colourless, odourless, and tasteless.

• It's a flammable gas.

• It is insoluble in water.

• It has a lower density than air

Chemical properties

• Reaction with halogens

H₂+X₂ →2 HX

• Reaction with dinitrogen

2H₂+O₂→ 2H₂O

• Reaction with metal

3H₂+N2673 K,200 atm ,Fe →2NH₃

• Reactions with metal ions and metal oxides

H₂+Pd²⁺ → Pd+2H⁺

yH₂+M_xO_y →xM^+y H₂O

• Reactions with organic compounds

H₂+CO+RCH=CH₂ → RCH₂CH₂CHO

H₂+ RCH₂CH₂CHO → RCH₂CH₂CH₂OH

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 5

Hydrides

Dihydrogen reacts with a variety of elements to form binary compounds known as hydrides.

Ionic hydrides

They are formed when high-reactivity metals of group 1 and group 2 combine with hydrogen. Lithium, Beryllium, and Magnesium hydrides have the maximum covalent nature of all. They are crystalline in structure and have a high melting and boiling point. They have a higher density than metals. They conduct electricity and release H2 gas when melted.

Covalent hydrides

They're mostly made up of p-block elements and a few s-block elements, which have a smaller electronegativity difference than hydrogen. They are binary compounds with covalent bond.They are of 3 types

• Electron deficient

They have fewer electrons than the octet. Eg:B₂H₆

• Electron precise

They have a sufficient number of electrons. Eg:CH₄

• Electron rich

They have additional electrons than the octet. Eg: NH₃

Molecular /non-stochiometric/interstitial hydrides

Molecular hydrides are produced when hydrogen reacts with the d and f elements in this reaction. Groups 6,7,8,9 and 3,4,5,10,11,12 do not produce hydrides, whereas group 3,4,5,10,11,12 can. This is referred to as the Hydride Gap (the inability of these groups to form hydrides is called Hydride gap). They don't have enough hydrogen. Non-stochiometric hydrides are another name for them. Interstitial spaces between these atoms are occupied by hydrogen.

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 6

Water

Water makes up roughly 65 percent of the human body, while it makes up nearly 95 percent of some plants.

Physical properties

• Water makes up roughly 65 percent of the human body, while it makes up nearly 95 percent of some plants.

• At 4°C, the maximum density of water is 1 gm cm^-3

• It is a tasteless, colourless liquid.

• Even covalent substances like alcohol and carbohydrates dissolve in water due to hydrogen bonding with polar molecules.

Structure of water

It is a bent molecule in gas phase, with a HOH bond angle of 104.5° and an O—H bond length of 95.7 pm. It has polar nature.

Structure of ice

The crystalline form of water is ice. Ice crystallizes hexagonally at atmospheric pressure. It condenses to cubic shape at low temperatures. Ice is lighter than water and has a lower density. As a result, ice cubes float in water.

Chemical properties

• Amphoteric nature

H₂O+NH₃ ↔ OH^- + NH₄⁺

H₂O+H₂S ↔ H₃O⁺ + HS^-

• Oxidizing and reducing nature

2H₂O+2Na → 2NaOH+H₂

6CO₂+12H₂O → C₆H₁₂O₆+6H₂O+6O₂

2F₂+2H₂O → 4H⁺+ 4F^-+O₂

• Hydrating tendency

P₄H₁₀+6H₂O → 4H₃PO₄

SiCl₄+2H₂O → SiO₂+4HCl

N₃^-+3H₂O → NH₃+3OH^-

• Hydrates formation

Coordinated water: [Cr(H₂O)₆]³⁺ 3Cl^-

Interstitial water: BaCl₂.2H₂O

Hydrogen bonded water:[Cu(H₂O)²⁺ SO₄^2-.H₂O

NCERT Class 11 Chemistry Chapter 8 Notes: Topic 7

Hardness of Water

The presence of calcium and magnesium (Ca²⁺ and Mg²⁺) salts in water causes this. The water containing these salts is called hard water. Magnesium bicarbonates, sulphates, chlorides, calcium bicarbonates, sulphates, and chlorides are the most common salts Calcium and magnesium salts in hard water react with soap to generate an insoluble precipitate known as scum. It sticks to the fabric.

2C₁₇H₃₅COONa+M²⁺ → (C₁₇H₃₅COO)2M ↓+2 Na

Temporary hardness

It is caused by the presence of calcium and magnesium bicarbonates in the water. It's called temporary since it's easy to get rid of by simply boiling hard water. It can be removed by

• Boiling

Mg(HCO₃)₂ ∆→ Mg(OH)₂↓+2CO₂

Ca(HCO₃)₂ ∆→ Ca(CO)₃↓+H₂O+CO₂

• Clark’s method

Ca(HCO₃)₂+Ca(OH)₂ → 2 Ca(CO)₃↓+2H₂O

Mg(HCO₃)₂+2Ca(OH)₂ → 2 Ca(CO)₃↓+Mg(OH)₂↓+2H₂O

Permanent hardness

It is caused by the presence of calcium and magnesium chlorides and sulphates.Chemical treatments can be used to remove permanent hardness from water.

• Treatment with washing soda

MCl₂+Na₂CO₃ MCO₃↓+2NaCl

MSO₄+Na₂CO₃ MCO₃↓+2Na₂ SO₄

• Calgon’s method

Na₂P₆O₁₈ → 2Na⁺+Na₄P₆O₁₈^2-

M²⁺+Na₄P₆O₁₈^2- → [Na₂MP₆O₁₈]^2-+2Na⁺

• Ion exchange method(Zeolite/permutit process)

2NaZ+M²⁺ MZ₂+ 2Na⁺

MZ₂+2NaCl → 2NaZ+MCl₂

NaZ-NaAlSiO₄(Zeolite)

• Synthetic resins method

Synthetic resin methods outperform ion exchange methods because they remove all forms of cations and anions, leaving only distilled water.

Cation exchange resin: It is made up of a massive hydrocarbon structure connected to fundamental groups. They are represented by the R-COOH or R-SO₃H general formula. This R stands for large hydrocarbon. These resins have the ability to exchange H+ions with cations found in hard water.

Anion exchange resin: An ion exchange resin is made comprised of a large hydrocarbon matrix that is connected to basic groups such as OH-ions, commonly in the form of substituted ammonium hydroxides. They are denoted by the letters R-NH₃OH, where R stands for large hydrocarbon framework. These resins may exchange hydroxide ions with anions found in hard water, such as chloride ions and sulphate ions.

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 8

Hydrogen Peroxide (H₂O₂)

Preparation

• BaO₂.8H₂O+H₂SO₄ → BaSO₄+H₂O₂+8H₂O

• 2HSO₄^- Electrolysis→ HO₃SOOSO₃ Hydrolysis→ 2HSO₄^-+2H⁺+H₂O₂

• 2-ethylanthraquinol O₂→ H₂O₂

Physical properties

• It is a clear liquid with no colour.

• It is miscible in all quantities with water and produces the hydrate H₂O₂. H₂O

Structure

H₂O₂ has a nonpolar structure.

Chemical properties

• Oxidation reactions in acidic medium

2Fe²⁺+2H⁺+H₂O₂ → 2Fe³⁺+2H₂O

PbS+4H₂O₂ → PbSO₄+4H₂O

• Oxidation reactions in basic medium

2Fe²⁺+H₂O₂ → 2Fe³⁺+2OH^-

Mn²⁺+H₂O₂ → Mn³⁺+2OH^-

• Reduction reactions in acidic medium

2MnO₄^-+6H⁺+5H₂O₂ → 2Mn²⁺+8H₂O+5O₂

HOCl+H₂O₂ → H₃O⁺+Cl^-+O₂

• Reduction reactions in basic medium

I₂+H₂O₂+2OH^- → 2I^-+2H₂O+O₂

2MnO₄^-+3H₂O₂ 2MnO₂+3O₂+2H₂O+2OH^-

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 9

Heavy Water (D₂O)

It is produced via electrolysis of water over a long period of time. It is employed in nuclear reactors as a moderator. It's used to investigate reaction mechanisms through exchange reactions. Heavy water is used for the preparation of other dueterium compounds.

CaC₂+2D₂O C₂ →D₂+Ca(OD)₂

SO₃+D₂O → D₂SO₄

Al₂C₃+12D₂O → 3CD₄+4Al(OD)₃

NCERT Class 11 Chemistry Chapter 9 Notes: Topic 10

Dihydrogen as a Fuel

The conveyance and storage of energy in the form of liquid or gaseous dihydrogen is the core premise of the hydrogen economy. The fact that energy is transmitted in the form of dihydrogen rather than electric power is an advantage. As a fuel, it has the following advantages: - It can be used in fuel cells to generate electricity. One of the key benefits of hydrogen combustion is that it produces very little pollution and does not emit any unburnt carbon particles in the form of smoke. The study shows that dihydrogen, both in gaseous and liquefied form, releases more energy when burned than other regularly used fuels. CNG is blended with 5% dihydrogen for use in four-wheeler vehicles.

Significance of NCERT Class 11 Chemistry Chapter 9 Notes

In Chemistry, hydrogen is a significant topic. It is appropriate for real-time applications and uses in our everyday life. Students can improve their final test scores by studying this Hydrogen Class 11 notes and learning about its real-world uses and applications, as well as how to employ it in real-time situations. Students can use the review Hydrogen Class 11 notes to gain a better understanding of the material and to answer the questions in the board exam as well as other competitive exams including NEET and JEE MAIN. Students can use Class 11 Chemistry chapter 9 notes pdf download for learning in offline mode.

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