What Are Hydrocarbons?

Hydrocarbons are organic compounds that are entirely made up of only two kinds of atoms – carbon and hydrogen. Typically, hydrocarbons are colourless gases that have very weak odours.

Hydrocarbons can feature simple or relatively complex structures and can be generally classified into four subcategories, namely alkanes, alkenes, alkynes, and aromatic hydrocarbons. 

The study of hydrocarbons can provide insight into the chemical properties of other functional groups and their preparation. Furthermore, hydrocarbons such as propane and butane are used for commercial fuel purposes in the form of Liquefied Petroleum Gas (LPG).

Benzene, one of the simplest aromatic hydrocarbons, serves as the raw material for the synthesis of many synthetic drugs.

Structure of Hydrocarbon

Table of Contents

The molecular formula for these compounds is C_xH_y. The existence of hydrocarbons is seen in plants and trees. For example, Carotenes is an organic pigment that is found in green leaves and carrots. These hydrocarbons make up 98% of natural crude rubber. Further, they possess large internal energy, which renders them their importance.

Classification and Types of Hydrocarbons

Earlier, chemists classified hydrocarbons as either aliphatic or aromatic. The classification was done based on their source and properties. And accordingly, it was found that aliphatic hydrocarbons were derived from the chemical degradation of fats or oils, whereas aromatic hydrocarbons contained substances that were a result of the chemical degradation of certain plant extracts. However, today we classify hydrocarbons on the basis of structure and not merely on their origin.

Classification of Hydrocarbons

Types of Hydrocarbons

• Saturated Hydrocarbons: In these compounds, carbon-carbon atoms and carbon-hydrogen atoms are held together by single bonds. These single-bonded compounds are the simplest hydrocarbons. These types of hydrocarbons don’t have double or triple bonds. In terms of hybridization, they have Sp³ hybridised carbon atoms with no Sp² or Sp hybridised carbon atoms. They are together called alkanes which have a general formula of C_nH_2n+2. For example, CH₄C₃H₆.
• Unsaturated Hydrocarbons: These compounds consist of a single, double or triple bond between carbon-carbon atoms. The double-bonded compounds are called alkenes, and the triple-bonded compounds are called alkynes. The general formula for alkenes is C_nH_2n, and for alkynes, the general formula is C_nH_2n-2.
• Cycloalkanes: These hydrocarbons possess one or multiple carbon rings. The hydrogen atom is attached to the carbon ring.
• Aromatic Hydrocarbons: They are also called arenes. Arenes are compounds which consist of at least one aromatic ring.
• Aliphatic Hydrocarbons: They are straight chain structures having no rings in them.
• Alicyclic Hydrocarbons: They are hydrocarbons having a ring structure in them. The carbons atoms can be Sp, Sp², or Sp³ hybridised.

Properties of Hydrocarbons

Due to their different molecular structures, the empirical formula of hydrocarbons is also different from each other. For instance, in alkanes, alkynes or alkenes, the amount of bonded hydrogen decreases in alkenes and alkynes. This is mainly due to the “self-bonding” or catenation of carbon that prevents the complete saturation of the hydrocarbon by the formation of double or triple bonds. The ability of hydrocarbons to bond to themselves is known as catenation. With such capabilities, they can form more complex molecules like cyclohexane and, in rare instances, aromatic hydrocarbons like benzene.

The cracking of Hydrocarbons is a process in which heavy organic molecules are broken down into lighter molecules. This is accomplished by supplying an adequate amount of heat and pressure. Sometimes, catalysts are used to speed up the reaction. This process plays a very important role in the commercial production of diesel fuel and gasoline.

Physical Properties

Alkanes with 10 C-atoms or less are generally gases at room temperatures of more than 10 C-atoms, and the molecules are gases or liquids. Alkanes generally have low boiling and melting points owing to their weak Vanderwal interaction.

The boiling point depends on the following factors:

Alkanes have high molecular mass and high boiling points. For example, C₂H₆ has more boiling point than CH_4.

Alkanes that have the same molecular mass but have a different number of branches, the one with less branching has a more boiling point. This is because Vanderwal’s force becomes weak as the area increases.

For example, CH₃-CH₂-CH₂-CH₃ has more boiling point. Alkanes are very feebly soluble in water, but they are soluble in non-polar solvents such as Benzene, CCl₄, etc.

Preparation of Hydrocarbons – Alkanes

From alkenes and alkynes

The alkanes can be produced from alkenes or alkynes through hydrogenation. H₂ gas is passed over a metal surface, such as Ni or Pt, along with the alkenes to produce alkane.

CH₂=CH₂ → (+Hz/Ni) CH₃-CH₃

The above reaction is called the “Sabatier-Sender son’s” reaction. Other catalysts which can be used are Pt, Pd-BaSo₄, Adams catalyst (Pt₂O) or Wilkinson catalyst (R₃PRhCl), etc.

From Alkyl Halides

Alkyl halides can be converted to alkanes through various methods. They are as follows.

1. Using Zn/Protic solvents

2. Using courts reactions

Note: Alkanes with only an even number of carbons atoms can be produced.

3. Using Reducing Agents

R-X → [H]R – H

The reducing agents which can be used are LiAlH₄, NaBH₄, NaNH₂, etc.

Note:

• LiAlH₄  can’t reduce 3° halides.
• NaBH₄ can’t reduce 1° halide.

2. From Aldehydes/Ketones

3. From Carboxylic Acids through Decarboxylation

Preparation of Hydrocarbons – Alkenes

General formula: C_nH_2n

Preparation Methods

Most of the reactions involving the preparation of alkenes involve an elimination process. There are 3 mechanisms suggested for the elimination reactions, and all these are β- eliminations.

E₂ Mechanism

• Second order kinetics
• Single step process
• Order & reactivity 1° > 2° > 3°

Because of steric hindrance,

• More favoured in non-polar, aprotic solvents.
• Less substituted alkenes formed as the major product.

E₁ Mechanism

• Two-step process
• 1^st order kinetics
• Order of reactivity: 3° > 2° > 1°

Because of the stability of carbonation,

• More favoured by polar, protic solvents.
• Rearrangement is possible.
• Gives more substituted alkenes as major products.

Hydration

(i) Acid catalysed

• Markovnikov product
• Rearrangement is possible.

(ii) Hydroboration-oxidation

• Anti – Markonikov
• No rearrangement

(iii) Oxymercuration-demercuration

• Markovnikov
• No rearrangement

Oxidation Reactions

• Using Baeyer’s reagent
• Using hot KMnO₄
• Ozonolysis
• Using O₅O₄
• Addition of peroxy acid

Preparation of Hydrocarbons – Alkynes

Alkynes can be prepared from alkyl halides and alcohols.

Addition reaction:

All addition reactions in alkenes are possible.

Benzene – Preparation

• From ethyne
• From phenol
• From aniline

Chemical Properties:

Benzene generally undergoes electrophilic substitution reactions.

Uses of Hydrocarbons

• Hydrocarbons are widely used as fuels. For example, LPG (Liquefied Petroleum Gas), and CNG (Liquefied Natural Gas).
• They are used in the manufacturing of polymers such as polyethene, polystyrene etc.
• These organic compounds find their application in the manufacturing of drugs and dyes as a starting material.
• They serve as lubricating oil and grease.

Frequently Asked Questions on Hydrocarbons

Q1

What are the 4 types of hydrocarbons?

Alkanes, Alkenes, Alkynes and Aromatic hydrocarbons are the 4 types of hydrocarbons.

Q2

What are hydrocarbons made up of?

Hydrocarbons are made up of the elements carbon and hydrogen. These compounds are dominant in crude oil, coal tar and waste products of pyrolysis.

Q3

What are the characteristics of hydrocarbons?

The characteristics of hydrocarbons are listed below:
Hydrocarbons are colourless and odourless.
They undergo a combustion reaction with oxygen giving carbon dioxide and water.
Greater the number of carbons, the greater the melting point of hydrocarbons.

Q4

Why are alkanes the least reactive hydrocarbons?

Alkanes are the least reactive hydrocarbons because of their stability. They contain only strong single sigma bonds. A high amount of energy is required to break sigma bonds, and thus they are the least reactive.

Q5

What is the product of ozonolysis of ethene?

Ethene on ozonolysis forms ozonide, which on further reduction with zinc dust, forms 2 molecules of formaldehyde.

Neeraj Anand, Param Anand

Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations. In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS". He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.

...

CBSE Class 11 Chemistry Syllabus

CBSE Class 11 Chemistry Syllabus is a vast which needs a clear understanding of the concepts and topics. Knowing CBSE Class 11 Chemistry syllabus helps students to understand the course structure of Chemistry.

Unit-wise CBSE Class 11 Syllabus for Chemistry

Below is a list of detailed information on each unit for Class 11 Students.

UNIT I – Some Basic Concepts of Chemistry

General Introduction: Importance and scope of Chemistry.

Nature of matter, laws of chemical combination, Dalton’s atomic theory: concept of elements,
atoms and molecules.

Atomic and molecular masses, mole concept and molar mass, percentage composition, empirical and molecular formula, chemical reactions, stoichiometry and calculations based on stoichiometry.

UNIT II – Structure of Atom

Discovery of Electron, Proton and Neutron, atomic number, isotopes and isobars. Thomson’s model and its limitations. Rutherford’s model and its limitations, Bohr’s model and its limitations, concept of shells and subshells, dual nature of matter and light, de Broglie’s relationship, Heisenberg uncertainty principle, concept of orbitals, quantum numbers, shapes of s, p and d orbitals, rules for filling electrons in orbitals – Aufbau principle, Pauli’s exclusion principle and Hund’s rule, electronic configuration of atoms, stability of half-filled and completely filled orbitals.

UNIT III – Classification of Elements and Periodicity in Properties

Significance of classification, brief history of the development of periodic table, modern periodic law and the present form of periodic table, periodic trends in properties of elements -atomic radii, ionic radii, inert gas radii, Ionization enthalpy, electron gain enthalpy, electronegativity, valency. Nomenclature of elements with atomic number greater than 100.

UNIT IV – Chemical Bonding and Molecular Structure

Valence electrons, ionic bond, covalent bond, bond parameters, Lewis structure, polar character of covalent bond, covalent character of ionic bond, valence bond theory, resonance, geometry of covalent molecules, VSEPR theory, concept of hybridization, involving s, p and d orbitals and shapes of some simple molecules, molecular orbital theory of homonuclear diatomic molecules(qualitative idea only), Hydrogen bond.

UNIT V – Chemical Thermodynamics

Concepts of System and types of systems, surroundings, work, heat, energy, extensive and intensive properties, state functions. First law of thermodynamics – internal energy and enthalpy, measurement of U and H, Hess’s law of constant heat summation, enthalpy of bond dissociation, combustion, formation, atomization, sublimation, phase transition, ionization, solution and dilution. Second law of Thermodynamics (brief introduction)
Introduction of entropy as a state function, Gibb’s energy change for spontaneous and nonspontaneous processes.
Third law of thermodynamics (brief introduction).

UNIT VI – Equilibrium

Equilibrium in physical and chemical processes, dynamic nature of equilibrium, law of mass action, equilibrium constant, factors affecting equilibrium – Le Chatelier’s principle, ionic equilibrium- ionization of acids and bases, strong and weak electrolytes, degree of ionization,
ionization of poly basic acids, acid strength, concept of pH, hydrolysis of salts (elementary idea), buffer solution, Henderson Equation, solubility product, common ion effect (with illustrative examples).

UNIT VII – Redox Reactions

Concept of oxidation and reduction, redox reactions, oxidation number, balancing redox reactions, in terms of loss and gain of electrons and change in oxidation number, applications of redox reactions.

UNIT VIII – Organic Chemistry: Some basic Principles and Techniques

General introduction, classification and IUPAC nomenclature of organic compounds. Electronic displacements in a covalent bond: inductive effect, electromeric effect, resonance and hyper conjugation. Homolytic and heterolytic fission of a covalent bond: free radicals, carbocations, carbanions, electrophiles and nucleophiles, types of organic reactions.

UNIT IX – Hydrocarbons

Classification of Hydrocarbons
Aliphatic Hydrocarbons:
Alkanes – Nomenclature, isomerism, conformation (ethane only), physical properties, chemical reactions.
Alkenes – Nomenclature, structure of double bond (ethene), geometrical isomerism, physical properties, methods of preparation, chemical reactions: addition of hydrogen, halogen, water, hydrogen halides (Markovnikov’s addition and peroxide effect), ozonolysis, oxidation, mechanism of electrophilic addition.
Alkynes – Nomenclature, structure of triple bond (ethyne), physical properties, methods of preparation, chemical reactions: acidic character of alkynes, addition reaction of – hydrogen, halogens, hydrogen halides and water.

Aromatic Hydrocarbons:

Introduction, IUPAC nomenclature, benzene: resonance, aromaticity, chemical properties: mechanism of electrophilic substitution. Nitration, sulphonation, halogenation, Friedel Craft’s alkylation and acylation, directive influence of functional group in monosubstituted benzene. Carcinogenicity and toxicity.

To know the CBSE Syllabus for all the classes from 1 to 12, visit the Syllabus page of CBSE. Meanwhile, to get the Practical Syllabus of Class 11 Chemistry, read on to find out more about the syllabus and related information in this page.

CBSE Class 11 Chemistry Practical Syllabus with Marking Scheme

In Chemistry subject, practical also plays a vital role in improving their academic scores in the subject. The overall weightage of Chemistry practical mentioned in the CBSE Class 11 Chemistry syllabus is 30 marks. So, students must try their best to score well in practicals along with theory. It will help in increasing their overall academic score.

CBSE Class 11 Chemistry Practical Syllabus

The experiments will be conducted under the supervision of subject teacher. CBSE Chemistry Practicals is for 30 marks. This contribute to the overall practical marks for the subject.

The table below consists of evaluation scheme of practical exams.

CBSE Syllabus for Class 11 Chemistry Practical

Micro-chemical methods are available for several of the practical experiments. Wherever possible such techniques should be used.

A. Basic Laboratory Techniques
1. Cutting glass tube and glass rod
2. Bending a glass tube
3. Drawing out a glass jet
4. Boring a cork

B. Characterization and Purification of Chemical Substances
1. Determination of melting point of an organic compound.
2. Determination of boiling point of an organic compound.
3. Crystallization of impure sample of any one of the following: Alum, Copper Sulphate, Benzoic Acid.

C. Experiments based on pH

1. Any one of the following experiments:

• Determination of pH of some solutions obtained from fruit juices, solution of known and varied concentrations of acids, bases and salts using pH paper or universal indicator.
• Comparing the pH of solutions of strong and weak acids of same concentration.
• Study the pH change in the titration of a strong base using universal indicator.

2. Study the pH change by common-ion in case of weak acids and weak bases.

D. Chemical Equilibrium
One of the following experiments:

1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of either of the ions.
2. Study the shift in equilibrium between [Co(H₂O)₆] ²⁺ and chloride ions by changing the concentration of either of the ions.

E. Quantitative Estimation
i. Using a mechanical balance/electronic balance.
ii. Preparation of standard solution of Oxalic acid.
iii. Determination of strength of a given solution of Sodium hydroxide by titrating it against standard solution of Oxalic acid.
iv. Preparation of standard solution of Sodium carbonate.
v. Determination of strength of a given solution of hydrochloric acid by titrating it against standard Sodium Carbonatesolution.

F. Qualitative Analysis
1) Determination of one anion and one cation in a given salt
Cations‐ Pb²⁺, Cu²⁺, As³⁺, Al³⁺, Fe³⁺, Mn²⁺, Ni²⁺, Zn²⁺, Co²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mg²⁺, NH₄ ⁺
Anions – (CO₃)^2‐ , S^2‐, NO₂^‐ , SO₃^2‐, SO^2‐ , NO ^‐ , Cl^‐ , Br^‐, I‐, PO₄^3‐ , C₂O²‐ ,CH₃COO^‐
(Note: Insoluble salts excluded)

2) Detection of ‐ Nitrogen, Sulphur, Chlorine in organic compounds.

G) PROJECTS
Scientific investigations involving laboratory testing and collecting information from other sources.

A few suggested projects are as follows:

• Checking the bacterial contamination in drinking water by testing sulphide ion
• Study of the methods of purification of water.
• Testing the hardness, presence of Iron, Fluoride, Chloride, etc., depending upon the regional
  variation in drinking water and study of causes of presence of these ions above permissible
  limit (if any).
• Investigation of the foaming capacity of different washing soaps and the effect of addition of
  Sodium carbonate on it.
• Study the acidity of different samples of tea leaves.
• Determination of the rate of evaporation of different liquids Study the effect of acids and
  bases on the tensile strength of fibres.
• Study of acidity of fruit and vegetable juices.

Note: Any other investigatory project, which involves about 10 periods of work, can be chosen with the approval of the teacher.

Practical Examination for Visually Impaired Students of Class 11

Below is a list of practicals for the visually impaired students.

A. List of apparatus for identification for assessment in practicals (All experiments)
Beaker, tripod stand, wire gauze, glass rod, funnel, filter paper, Bunsen burner, test tube, test tube stand,
dropper, test tube holder, ignition tube, china dish, tongs, standard flask, pipette, burette, conical flask, clamp
stand, dropper, wash bottle
• Odour detection in qualitative analysis
• Procedure/Setup of the apparatus

B. List of Experiments A. Characterization and Purification of Chemical Substances
1. Crystallization of an impure sample of any one of the following: copper sulphate, benzoic acid
B. Experiments based on pH
1. Determination of pH of some solutions obtained from fruit juices, solutions of known and varied
concentrations of acids, bases and salts using pH paper
2. Comparing the pH of solutions of strong and weak acids of same concentration.

C. Chemical Equilibrium
1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing
the concentration of eitherions.
2. Study the shift in equilibrium between [Co(H2O)6]2+ and chloride ions by changing the
concentration of either of the ions.

D. Quantitative estimation
1. Preparation of standard solution of oxalic acid.
2. Determination of molarity of a given solution of sodium hydroxide by titrating it against standard
solution of oxalic acid.

E. Qualitative Analysis
1. Determination of one anion and one cation in a given salt
2. Cations – NH+4
Anions – (CO3)2-, S2-, (SO3)2-, Cl-, CH3COO-
(Note: insoluble salts excluded)
3. Detection of Nitrogen in the given organic compound.
4. Detection of Halogen in the given organic compound.

Note: The above practicals may be carried out in an experiential manner rather than recording observations.

We hope students must have found this information on CBSE Syllabus useful for their studying Chemistry. Learn Maths & Science in interactive and fun loving ways with ANAND CLASSES (A School Of Competitions) App/Tablet.

Frequently Asked Questions on CBSE Class 11 Chemistry Syllabus

Q1

How many units are in the CBSE Class 11 Chemistry Syllabus?

There are 9 units in the CBSE Class 11 Chemistry Syllabus. Students can access various study materials for the chapters mentioned in this article for free at ANAND CLASSES (A School Of Competitions).

Q2

What is the total marks for practicals examination as per the CBSE Class 11 Chemistry Syllabus?

The total marks for the practicals as per the CBSE Class 11 Chemistry Syllabus is 30. It includes volumetric analysis, content-based experiment, salt analysis, class record, project work and viva.

Q3

Which chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry?

The organic chemistry chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry.