2nd Year Chemistry Chapter 8 (Aliphatic Hydrocarbons) Online Preparation

Question # 1

Describe a test for the presence of unsaturation in organic molecules.

Ans 1: When alkenes are treated with mild oxidizing reagents like dilute alkaline KMnO₄solution (Bayer's Reagent) at low temperature,hydroxylation of double bond occur resulting in the formation of dihydroxy compounds known as vicinal glycols. The pink colouration of KMnO₄solution is discharged.
3CH₂=CH₂+ 2KMnO₄+ 4H₂O---->HO-CH₂-CH₂-OH+2MnO₂+2KOH

Question # 2

Distinguish between Ethene and Acetylene?

Ans 1: Ethene and acetylene both are un-saturated compounds. Ethene contains sigma-bond,having partially fiiled p-orbitals overlap in a parallel fashion.sigma-electron are less firmly held between the nuclie. In ethene a sigma-bond is a weak bond.
Ans 2: In actetylene,the carbon atoms are held together by a triple bond,a o-bond and two sigma-bond.The electron density between the carbon atoms is very high which draws atoms very close to each other.Electron in a triple bond are,therefore,less exposed and thus less reactive towards reagents than ethene.

Question # 3

Why are alkenes also called olefins?

Ans 1: Alkenes also known as olefins(derived from Latin word olefiant meaning oil forming ) because its lower members from oily products on treatment with chlorine or bromine.

Question # 4

Explain acidic nature of ethyne?

Ans 1: Ethnelnethyne,the hydrogen atom is bonded to the carbon atom with sp-s overlap.The sp hybridized carbon atom of ethyne pulls the electrons more strongly making the attached hydrogen atom slightly acidic as:H-C=C^-8-H⁺⁸

Question # 5

How common name of alkenes are derived?Give common names of CH₂=CH₂and CH₃-CH₂=CH_2?

Ans 1: For alkanes the word is derived from the Greek or Latin numerals indicating the number of carbons atom in molecule and the name is completed by adding ane as a suffix.Alkenes are similarly named by replacing the ending "ane" of the name of alkane with "ylene".

Question # 6

Write structural formulas for two compound;i) Vinyl acetylene ii) But-3-en-yne

Ans 1: i) Vinyl acetylene: CH₂=CH-C=CH
Ans 2: ii) 1-Butene-3-yne: CH₂=CH-C=CH

Question # 7

How can ethyne be prepared commercially from calcium carbide?

Ans 1: On industrial scale ethyne is prepared by the reaction of calcium carbide (CaC₂) with water.Calcium carbide is prepared by heating lime (CaO) and coke (C) at a very high temperature in an electric furnace.
CAO + C------>CaC₂+ CO
CaC₂+2H₂O------->Ca(OH)₂+ HC=CH

Question # 8

Alkanes are less reactive than alkenes. Comment?

Ans 1: The alkanes or paraffins(Latin: parum=little,affins=affinity) under ordinary condition are inert towards acids,alkalis,oxidizing and reducing agents.The un-reactivity of alkanes can also be explained on the basis of inertness of a o-bond.In a o-bond the electrons are very tightly held between the nuclei which makes it is very stable bond.A lot of energy is required to break it.
Ans 2: On the other hand alkenes contains sigma-bond,having partially filled p-orbitals overlap in a parallel fashion.sigma-electron are less firmly held between the nulei. In alkenes a sigma-bond is,therefore,a weak bond as compared to a o-bond.

Question # 9

Define Hydrogenation,

Ans 1: Hydrogenation is a process in which molecule of hydrogen added to an alkene in the presence of a catalyst and at moderate pressure (1-5 atm ) to give a saturated compound.

Question # 10

How ethene can be prepared by Kolb's electrolysis?

Ans 1: When a concentrated solution of sodium or potassium of a monocarboxylic acid is electrolyzed an alkane is produced this method is only suitable foe the preparation of symmetrical alkanes.

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2nd Year Chemistry Chapter 8 (Aliphatic Hydrocarbons) Online Preparation

Online Short Questions For Chapter 8 "12th Class Chemistry Chapter 8 Short Questions Preparation "

Chemistry - 12th Class Chemistry Chapter 8 Short Questions Preparation

Describe a test for the presence of unsaturation in organic molecules.

Distinguish between Ethene and Acetylene?

Why are alkenes also called olefins?

Explain acidic nature of ethyne?

How common name of alkenes are derived?Give common names of CH2=CH2and CH3-CH2=CH2?

Write structural formulas for two compound;i) Vinyl acetylene ii) But-3-en-yne

How can ethyne be prepared commercially from calcium carbide?

Alkanes are less reactive than alkenes. Comment?

Define Hydrogenation,

How ethene can be prepared by Kolb's electrolysis?

Prepare Complete Set Wise Questions For Chapter 8 "12th Class Chemistry Chapter 8 Short Questions Preparation "

Set 1

Set 2

12th Class Chemistry Chapter 8 Short Questions Preparation - Set 1

Describe a test for the presence of unsaturation in organic molecules.

Distinguish between Ethene and Acetylene?

Why are alkenes also called olefins?

Explain acidic nature of ethyne?

How common name of alkenes are derived?Give common names of CH2=CH2and CH3-CH2=CH2?

Write structural formulas for two compound;i) Vinyl acetylene ii) But-3-en-yne

How can ethyne be prepared commercially from calcium carbide?

Alkanes are less reactive than alkenes. Comment?

Define Hydrogenation,

How ethene can be prepared by Kolb's electrolysis?

12th Class Chemistry Chapter 8 Short Questions Preparation - Set 2

Explain Markovnikov rule with one example,

What is heat of combustion?

Mention four uses of ethene.

How can ethyne be prepared commercially from calcium carbide?

Identify the actual product ,when HBr is added to propene.

What is Hydrogenolysis?Give an example.

How ethene can be prepared by Kolb's electrolysis?

Why ethene is more reactive than ethyne towards additions reactions?

What is effect of branching on boiling of alkanes?

Define Ramy nickel.Give its use.

12th Class Chemistry Chapter 8 Preparation

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How common name of alkenes are derived?Give common names of CH₂=CH₂and CH₃-CH₂=CH_2?

How common name of alkenes are derived?Give common names of CH₂=CH₂and CH₃-CH₂=CH_2?