10th Class Chapter 4 Chemistry Long Questions

Preparaton of alkanes:

As e know alkanes from a series of homologous compounds.So, their methods of preparation and chemical properties are similar. Although ,there are many methods of preparation, but only two methods are discussed here.

Hydrogenation of alkanes and alkanes:

Hydrogenation means addition of molecular in alkanes and alkanes ,as we know alkanes alkanes are unsaturated compounds, so they have the capacity to add up atom in them.This reaction is carried out in the presence of nickel catalyst at 250 °C to 300 °C .However in the presence of catalyst platinum or palladium ,the reaction takes place at room temperature ,such as:

H2C= CH2+H2 pd/pt H3C-CH3

Similarly;

HC=CH +H2 Ni H2C = CH2

250-300°C

H2C =CH2+H2 Ni H3C – CH3

250-300 °C

Reduction of alkanes:

Reduction means addition of nacent hydrogen.Infact ,It is a replacement of a halogen atom with a hydrogen atom. This reaction takes place in the preence of Znmetal and HCL.

CH3Br +2[H] zn/dil.HCL CH4+HB

CH3CH2Br +2[H] zn/dil.HCL CH3-CH3+HBr

Physical properties of alkenes;

Alkenes form a homologous series of compounds,first four members of the series are gases the alkanes consisting of C5 to C10 are liquids while higher members of the series are solids.

They are nonpolar, therefore they are insoluble in water but soluble in organic solvents.

The density of alkenes increase gradually with the increases of molecular size.

The melting and boiling points of alkanes increase regularly with the increase of molecular sizes this is because of increase o attractive forces between the molecules of alkanes.

The become more viscous as their molecular sizes incease.

Alkanes become less flammable,i.e more difficult to burn with the increase of molecular sizes.

Oxidation of alkanes with KMnO4:

Alkanes colourized the pink color of acidified dilute solution of potassium permanganate because the double bond electrons are with Mno4 ion, which further goes on to form MNO and other glycol such as there is addition.

3CH2 = CH2+2KL4No4+4H2OA_______ 3H2O- OH

2MnO2+2KOH

This reaction is also used to test unsaturation in an organic compounds.

Physical properties:

Alkanes also from a series of compounds. Its first member is acetylene is a colorless gas with faint garlic odour.

Acetylene is lightly soluble in water but soluble in organic solvents such as benzene alcohol, acetone ether etc.

Acetylene is slightly lighter then air.

Alkanes are also flammable.They produce smokier flames than those of alkenes and alkenes.

Uses of acetylene:

Acetylene produc oxy- acetylene flame with oxygen.it is a highly exothermic reaction.Heat released is used for welding purposes.

Acetylene is used to prepare other chemical,such a alcohols, acetaldehyde and acids.

It is used for the ripening of fruits.

It is used for the manufacturing of polymer products like polyvinyl chloride,polyvinyl acetate and synthetic rubber like neoprene.

It is polymerized to form benzene , which is used a raw material to form a variety of organic compounds.

The hydrocarbon in which all the four valencies of carbon atoms are fully satisfied (saturated) by single bond with other carbon atoms and hydrogen atom are saturated hydrocarbon.

Unsaturated hydrocarbon:

The hydrocarbons in which two carbon atoms are linked by a double or a triple bond are called unsaturated hydrocarbon.

Alkyl halides are reduced to alkanes with nascent hydrogen which is obtained by the action of zn with ditute HCL.

Since lower members of alkane form oily products on treatment with cl2 or Br2 therefore alkenes are also called olefins .

Methane CH4

Ethane CH3- CH3

Because burning of alkanes in the presence of excess of air or oxygen produces a lot of heat therefore alaknes are used as fuel.

Elthylene or eltene CH2= CH2

Propylene or propore CH3-CH=CL

CH3-CH_____OH+HOS3H____CH3-CH3____OSO3H +H2O

CH3-CH2-OSO3H_______CH2 = CH2+H2SO4

The hydrocarbons containing carbon carbon single bonds in their molecular are called alkanes:

H H H

H*C*C*C*H

H H H

The main sources of alkanes are petroleum and natural gas natural gas contain about 58% of methane.

A chain of carbon atoms in which one carbon atom is attrached to more then two other carbon atom is called straight chain , a chain of carbon atom is which at least one carbon atom is attached to three or four other carbon.

Since in alkanes all bonds are single bonds which are very strong therefore alkanes give only substitution reaction.

Ethene is used for artificial ripening of fruits it is used as a general anaesthetic.

Alkanes are reaction compound because the electrons of the double bond are easily available for reaction,as a result one of the bond of a double bond gets taken and two new single bonds are formed.

Ethene is used for artificial ripening of fruits ,it is used as a general anaesthetic .

A substitution reaction in which are or monohydrogen atoms of a alkane are replaced by halogen atom is called hologention

CH 4_______ C+4HCL

The hydrocarbons in which first and the last carbon are not directly joined to each other are called open chain hydrocarbons.

Methane is called as marsh gas because it is produced when vegolation decomposed naturaly within some geographical marhas swamps and bogs.

Acetylene is slightly lighter than air, alkynes are flammable they produce smokier falmes than those of alkanes and alkanes.

Ethene is slightly less then air alkanes are non polar they are insoluble in water but soluble in organic solvents such as alcohol.

On heating ethyl bromide with alcohol KOH ethare is formed removal of halogen and hydrogen takes place from adjacent carbon atoms to create a double bond.

The addition of hydrogen across a double bond is called hydrogenation

CH2= CH2+H2 ________CH3-CH3

Ethane ________ ethane

Alkynes are hydrocarbons that contain carbon-carbon triple bond the simplest alkyne is acetylene (CH= CH) they have general formula CoH2O.

Alkanes cannot be oxidized with KMNO4 because alkanes and aromatic compounds do not react with potassium permanganate.

These are the reaction in which the product formed by the addition of some reagens like H2,CL2, etc,

CH2 =CH2+H2________H3C –CH2