CBSE Class 11 Chemistry VBQs Some Basic Concept In Organic Chemistry

Question. Three students Vaibhav,Vishal and Vikas were determining the elements present in given organic compound by Lassaigne’s test. Vaibhav added FeSO₄ and dil. H₂SO₄ acid to Na- extract and observed Prussian blue colour. Vishal was keeping some pieces of sodium metal in his pocket, Vikas asked him not to do so. Now answer the following questions.

(a) Name the element present in the organic compound.
Answer: Nitrogen

(b) Write the test for chlorine
Answer:  sodium fusion extract + silver nitrate solution = white ppt

(c) Write the value associated.
Answer: Scientific attitude/concern for others

Question. An organic compound on heating changes directly into vapours without undergoing into liquid state, it is insoluble in water and is commonly used to prevent clothes against moths. It is contaminated with cinnamaldehyde.Naresh, a student of class XI was asked by his teacher how to purify it.Now answer the following questions

(a) Which method of purification would Naresh apply?
Answer: Sublimation

(b) Name the compound and write it’s another use.
Answer: Naphthalene and can be used as freshener

(c) Write the value associated with this.
Answer: Scientific attitude

Question. Carbon shows a unique property to form a large number of organic compounds. Even towards the end of 19th century the number of organic compounds known was difficult to remember by their common names. In order to systematize the naming of organic compounds IUPAC system of nomenclature was first introduced in 1947and is modified from time to time. Based on these facts now answer the following questions:

(a) Name the property of carbon to link itself to form a large number of compounds.
Answer:  Catenation

(b) Write the IUPAC name of CH₃ CH=CH CH (Br) CH₃ and trivial name of CH₃– C (CH₃)₂ – CH₃.
Answer: 4-Bromopent-2-ene, Neo-pentane

(c) Write the value associated with property of carbon.
Answer: integration / group works

Organic Chemistry

Introduction and Vital Force Theory

Carbon exhibits tetravalency.

Carbon has the ability to successively bond to other carbon atoms to form long chain. The property of carbon is called as catenation.

Carbon also forms covalent bonds with hydrogen, oxygen, nitrogen, sulphur and halogens. These complex carbon compounds are known as organic compounds.

The branch of chemistry that studies the formation and properties of organic compounds is known as organic chemistry.

Organic compounds made of only hydrogen and carbon atoms are known as hydrocarbons.

Isomerism

The existence of two or more compounds with the same molecular formula but different properties is known as isomerism. The compounds themselves are called as isomerism.

A compound having same molecular formula but different structures i.e. the way by which the atoms are linked is called as structural isomers and the phenomena is known as structural isomerism.

Compounds that have the same molecular formula but different carbon chain, that is, straight or branched chain are known as chain isomers, and the phenomenon is known as position isomerism.

Compounds that have same molecular formula, same chain but which differ in the position of the substituent or functional group are known as position isomers, and the phenomenon is known as position isomerism.

The compound having same molecular formula but different functional groups is called as functional isomers and the phenomenon is known as functional isomerism.

The compound having same molecular formula but different alkyl groups attached to the same functional group are called as metamers and the phenomenon is known as stereoisomerism.

The isomers which possess the same structural formula but differ in three dimensional arrangements of atoms or groups in space within the molecule are known as stereoisomerism.

Organic Compounds: Nomenclature - General Rules

The system of assigning a name to a compound is known as nomenclature.

The trivial names are given on the basis of the source and certain properties of organic compounds.

The IUPAC system is a systematic nomenclature in which the name of a compound correlated to its molecular structures

The IUPAC name of an organic compound consists of three parts the word root, the suffix and the prefix.

The word root indicates the number of carbon atoms present in the selected longest chain.

A primary suffix is added to the end of the root word. It indicates if a compound is saturated or unsaturated, that is if a single or multiple bonds is present.

A secondary suffix indicates the nature of the functional group present in a compound.

A primary prefix is used to differentiate acyclic compounds.

In the IUPAC system some groups are not considered as functional groups; they are treated as substituent groups. In such cases, the substituent acts as the secondary prefix.

Preparation, Properties and Uses of Methane

Methane is a hydrocarbon with the molecular formula CH₄.

When carbon monoxide is heated with hydrogen over nickel at 300°C, methane and water are formed.

Methane is prepared in the laboratory by heating sodium acetate with sodium hydroxide and calcium oxide.

Methane is a colourless and non- poisonous gas, insoluble in water and lighter than air.

It is one of the main causes of the greenhouse effect.

Methane undergoes substitution reactions with chlorine. Preparation, Properties and Uses of Ethene

Ethene is the first member of the unsaturated aliphatic hydrocarbon series and has a double bond.

Ethene is also known as ethylene.

When chloroethane is treated with alcoholic potassium hydroxide, ethene is formed.

Dehydration of ethyl alchol, dehydrohalogenation of bromoethane and dehydrohalogenation or cracking are the various ways to produce ethene in the laboratory.

Ethene is colourless gas with a pleasant odour at STP.

Ethene reacts with hydrogen in the presence of nickel to give ethane.

Ethene is an essential ingredient of synthetic chemicals such as ethylene glycol, diethyl ether, ethylene oxide and mustard gas.

Preparation, Properties and Uses of Ethyne

Ethyne is lighter than air, slightly soluble in water but completely soluble in organic solvent and colourless gas with odour of ether.

It melts at -82°C, and its boiling point -75°C.

Ethyne shows various chemical reaction like catalytic hydrogenation, halogenations, oxidation or combustion and polymerisation. It also reacts with metal ions in ammoniacal cuprous chloride and ammoniacal silver nitrate to form acetylides of heavy metals.

Ethyne has many applications like it is used in preparation of various oraganic compounds and synthetic products, artificial ripening and preservation of fruits, acetylene lamps and producing oxyacetylene flame.

Carbon and its Compounds - Hydrocarbons

Carbon exists in a large number of organic compounds.

Carbon shares its four electrons with other atoms forming four covalent bonds. The property is known as tetra valency.

Carbon atoms are capable of forming multiple bonds with carbon compounds.

The phenomenon of self linkage among identical atoms to form long chains is known as catenation.

The members of a homologous series are represented by a general formula.

The different between any two consecutive members in a homologous series is by a CHz group.

The members of a homologous series are prepared by similar methods.

There is a gradation in the physical properties of the members of a homologous series.

Preparation, Properties and Uses of Methanol

Methanol can be prepared by prepared by the hydrolysis of bromomethane, as well as mixing water gas hydrogen in the right proportions.

Methanol is a colourless, odourless, Volatile and inflammable liquid.

Methanol reacts with sodium to form sodium acetate and hydrogen gas.

On oxidation, methanol initially forms formaldehyde and then forms formic acid.

Methanol reacts with acetic acid to form methyl acetate, which is an ester.

Methanol is used as a solvent and anti- freezing agent.

Methanol is also used in manufacturing industrially important chemicals, like formaldehyde and formic acid.

Important Carbon Compounds

Ethanol is prepared by the fermentation of cane sugar or molasses.

Properties of Ethanol:
• Ethanol readily reacts with sodium metal to give sodium ethoxide and hydrogen gas.
• Ethanol, on heating to a temperature of 443 degrees Kelvin with excess concentrated sulphuric acid, gives ethane.

Uses of Ethanol:
• Ethanol is used in the manufacture of alcoholic beverages, Pharmaceutical products anti freezing agents for automobiles.

Ethanoic acid is colourless pungent odoured liquid which is miscible with water =, ether and ethyl alcohol.

Properties of Ethanoic acid:
• Reacts with carbonates and bicarbonates to give sodium acetate and carbon dioxide.
• Reacts with bases like sodium hydroxide to give sodium acetate and water.
• Rreacts with ethanol in the presence of concentrated sulphuric acid to undergo an esterification reaction.

Saponification is getting back ethanol and ethanoic acid from an ethyl acetate.

Ethanoic acid is used:
• As a preservative of food items.
• In the manufacture of artificial fibres.
• For the coagulation of latex.

Alkanes: Nomenclature and Isomerism

Alkanes are the simplest form of hydrocarbon containing only carbonandhydrogen.
Its molecules consist of carbon- carbon single bonds and carbon- hydrogen bonds.

Their general formula is C_nH_2n=+2.

Alkane series can be obtained by replacing one of the hydrogen atoms of methane by the- CH₃ group.

Depending on the number of carbon atoms that a single that a single carbon atom is attached to, the carbon atom can be called as primary, secondary, tertiary or quarternary.

Higher alkanes with more than one structure are called isomers.

The properties of alkanes depend on their structure, and hence, it is important to be able to name them and to be able to draw their structures from a given name.

Alkanes: Properties

Physical properties of alkanes depend on the Van der waals forces between molecules.

Linear or straight chain alkanes have a higher boiling point than its branched isomers.

Alkanes are mostly inert, but also do undergo substitution reactions under certain conditions.

Alkenes: Nomenclature and Isomerism

The unsaturated hydrocarbon with a double bond in between carbon atoms are known as alkenes.

The general molecular formula of Alkenes is C_nH_2n.

In the IUPAC system, alkenes are named by replacing the ‘ane’of the

corresponding alkanes by the suffix ‘ene’.

Alkenes show structural as well as stereo isomerism.

In structural isomers, alkanes show chain and position isomerism.

In the isomerism, they show cis and trans isomerism.

Trans isomers are more stable than cis isomers.

Alkynes: Nomenclature and Isomerism

The group of unsaturated hydrocarbons with the general formula, C_nH_2n-2, is known as alkynes.

Alkynes contain at least on triple bond between two carbon atoms.

In the IUPAC system, alkynes are named by replacing the ‘ane’ of the corresponding alkanes by the suffix ‘yne’.

When two compounds differ in their structure due to the position of the triple bond, they are known as position isomers.

As a triple bond is shorter, it is stronger compared to single and double bonds.

Carboxylic Acids: Nomenclature

Organic compounds that contain the carboxyl functional group,- COOH, are called carboxylic acids.

Higher members of aliphatic carboxylic acids are known as fatty acids.

In the common system, aromatic acids are named as the derivatives of benzoic acid, C₆H₅COOH.

In the IUPAC system, carboxylic acids are named by replacing the ending ‘e; of the corresponding alkane by ‘-oic acids’ to form alkanoic acid.

Compound with more than one carboxyl group are named by retaining the ending ‘e’ of the alkane, and adding the multiplicative prefix di, tri, etc. to the term ‘-oic acid’.