[3 Mark Question Answer]

Question 13 Marks

What are Hydrocarbons? Compare saturated and unsaturated hydrocarbons?

Answer

Hydrocarbons are compounds that are made up of only carbon and hydrogen.
Comparison of saturated and Unsaturated hydrocarbons:

Saturated Hydrocarbon	Unsaturated Hydrocarbon
1. Carbon atoms are joined only by single bonds.	Carbon atoms are joined by double or by triple bonds.
2. They are less reactive due to the non-availability of electrons in the single covalent bond.	They are more reactive due to the presence of electrons in the double or the triple bond.
3. They undergo a substitution reaction.	They undergo addition reaction.

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Question 23 Marks

Give the names and the structural formula of the first three members of the homologous series of alkanes.

Answer

The names and the structural formula of first three members of the homologous series of alkane are:
(i) $CH_4$ Methane

(ii) $C_2H_6$ Ethane

(iii) $C_3H_8$ Propane

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Question 33 Marks

Give the names of any three alkyl radicals. How are they formed?

Answer

The name of three alkyl radicals are:
Methyl
Ethyl
Propyl
They are formed by removing 1 hydrogen from an alkane.
$CH_4 \rightarrow-CH_3+H^{+}$
Methyl
$CH_3-CH_3 \rightarrow CH_3-CH_2-+H^{+}$
Ethyl
$CH_3-CH_2-CH_3 \rightarrow CH_3-CH_2-CH_2-+H^{+}$
Propy

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Question 43 Marks

Explain the following : Catenation

Answer

Catenation: The property of self -linking of atoms of an element through covalent bonds in order to form straight chains, branched chains and cyclic chains of different sizes is known as catenation.
Carbon- carbon bond is strong so carbon can combine with other carbon atoms to form chains or rings and can involve single, double and triple bonds.

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Question 53 Marks

Explain the following : Tetravalency

Answer

Tetravalency: Carbon can neither lose nor gain electrons to attain octet. Thus it shares four electrons with other atoms. This characteristics of carbon by virtue of which it forms four covalent bonds, is called Tetravalency of carbon.
In structural form :

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Question 63 Marks

Organic chemistry plays a key role in all walks of life. Discuss

Answer

Organic compounds are present everywhere. They are present in :
It is present in the production of soaps, shampoos, powders and perfumes.
It is present in the food we eat like carbohydrates, proteins, fats, vitamins etc.
Fuel like natural gas, petroleum are also organic compounds.
Medicines, explosives, dyes, insecticides are all organic compounds.
Thus we can say that organic compounds play a key role in all walks of life.

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Question 73 Marks

Define a functional group and give the structural formula of the following functional group:
(a) Ketons
(b) Alcohols\
(c) Aldehydes

Answer

The names and the structural formula of first three members of the homologous series of alkane are:
(i) $CH_4$ Methane

(ii) $C_2H_6$ Ethane

(iii) $C_3H_8$ Propane

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Question 83 Marks

Define the substitution and addition reaction. Give an example for each.

Answer

Substitution reaction: A reaction in which one atom of a molecule is replaced by another atom (or group of atoms) is called a substitution reaction.
Addition reaction: A reaction involving the addition of atom(s) or molecules(s) to the double or the triple bond of an unsaturated compound so as to yield a saturated product is known as addition reaction.

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Question 93 Marks

What is the Vital force theory? Why was it discarded?

Answer

Vital Force Theory is a theory made by the Scientist Berzelius in 1809 which assumed that organic compounds are only formed in living cells and it is impossible to prepare them in laboratories.
It was discarded because Friedrich Wohler showed that it was possible to obtain an organic compound(urea) in the laboratory.

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Question 103 Marks

Give at least one example in case to show structure of isomers of triple bond compound ?

Answer

Triple bond compound: In case of Hexyne:

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Question 113 Marks

How is acetic acid prepared from acetylene?

Answer

Acetylene is first converted to acetaldehyde by passing through $40 \%$ $H _2 SO _4$ at $60^{\circ} C$ in the presence of $1 \% HgSO _4$.
The acetaldehyde is then oxidised to acetic acid in the presence of catalyst manganous acetate at $70^{\circ} C$.
$
\begin{array}{c}
C _2 H _2+ H _2 O \xrightarrow[ HgSO _4]{ H _2 SO _4(\text { dil })} CH _3 CHO \\
CH _3 CHO + O _2 \xrightarrow[\text { Catalyst }]{\Delta} 2 CH _3 COOH
\end{array}
$

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Question 123 Marks

Give the structural formulae of acetic acid? IUPAC name of acetic acid. What is glacial acetic acid?

Answer

The structural formula of acetic acid:

IUPAC name of acetic acid is:
Ethanoic acid
Glacial acetic acid is the pure form of acetic acid. It does not contain water.

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Question 133 Marks

Name the products formed and give appropriate chemical equations for the Ethanol oxidized by acidified potassium dichromate ?

Answer

Ethanol oxidized by $K _2 Cr _2 O _7$ :
$
C _2 H _5 OH \xrightarrow{ O } CH _3 CHO + H _2 O \xrightarrow{ O } CH _3 COOH
$
Alcohols get oxidized and get converted into ethanal and then into acetic acid.

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Question 143 Marks

Name the product formed when ethanol reacts with acetic acid. Give an equation.
What is the name given to this type of reaction?

Answer

When ethanol reacts with acetic acid ethyl acetate is formed.
$
C _2 H _5 OH + CH _3 COOH \xrightarrow{\text { conc } \cdot H _2 SO _4} CH _3 COOC _2 H _5+ H _2 O
$
This reaction is known as an esterification reaction.

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Question 153 Marks

State the method of preparation of ethanol by hydrolysis of ethane.

Answer

By hydrolysis of ethene: When concentrated sulphuric acid is added to ethene at a temperature of $80^{\circ} C$ and pressure of $30$ atm . ethyl hydrogen sulphate is produced. Ethyl hydrogen sulphate on hydrolysis with boiling water gives ethanol.

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Question 163 Marks

Ethanol can be converted into ethene which can be changed into ethane. Choose the correct
word or phrase from the brackets to complete the following sentences.
(a) The conversion of ethanol into ethene is an example of ___________
(b) Converting ethanol into ethene requires the use of ___________
(c) The conversion of ethene into ethane is an example of ___________
(d) The catalyst used in the conversion of ethene into ethane is commonly ___________

Answer

(a) The conversion of ethanol into ethene is an example of Dehydration.
(b) Converting ethanol into ethene requires the use of Conc. $H_2SO_4$.
(c) The conversion of ethene into ethane is an example of hydrogenation.
(d) The catalyst used in the conversion of ethene into ethane is commonly nickel.

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Question 173 Marks

Ethanol can be oxidized to ethanoic acid. Write the equation and name the oxidizing agent.

Answer

$
C _2 H _5 OH \xrightarrow{ O } CH _3 CHO + H _2 O \xrightarrow{ O } CH _3 COOH
$
The oxidizing agents that can be used are potassium dichromate and potassium permanganate.

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Question 183 Marks

Give a chemical test to distinguish between of ethene (ethylene) and ethyne (acetylene) ?

Answer

Chemical test to distinguish :
Ethene and ethyne

Sl. No.	Test	Ethene	Ethyne
1	On adding a few drops of ammonical cuprous chloride to the hydrocarbon	No change is observed	Red precipitate of copper acetylide is formed
2	On adding ammonical silver nitrate	No observation	White precipitate of silver acetylide is formed.

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Question 193 Marks

Give a chemical test to distinguish between of ethane and ethene ?

Answer

Chemical test to distinguish :
Ethane and ethene

Sl. No	Test	Ethane	Ethene
1	On adding a few drops of bromine solution in carbon tetrachloride to the hydrocarbon	No change is observed	The reddish brown colour gets decolorized
2	On adding a few drops of alkaline potassium permanganate (purple colour) to the hydrocarbon	No change is observed	The purple colour fades.

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Question 203 Marks

Draw a diagram of acetylene prepared in the laboratory?

Answer

Diagram of acetylene preparation:

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Question 213 Marks

Give reason:
Hydrocarbons are excellent fuels.

Answer

Hydrocarbons such as alkanes undergo combustion reactions with oxygen to produce carbon dioxide and water vapour. Alkanes are flammable which makes them excellent fuels.
Methane, for example, is the principal component of natural gas.
$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$

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Question 223 Marks

Name the products formed and write an equation when ethyne is added to the following in an inert solvent:
Bromine

Answer

Ethyne in an inert solvent of carbon tetrachloride adds chlorine to change into 1,2-dichloro ethene with carbon-carbon double bond, and then to 1,1,2,2-tetrachloro ethane with carbon-carbon single bond.
$
C _2 H _2 \xrightarrow{ Cl _2} C _2 H _2 Cl _2 \xrightarrow{ Cl _2} \longrightarrow C _2 H _2 Cl _4
$

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Question 233 Marks

Name the products formed and write an equation when ethyne is added to the following in an inert solvent:
Chlorine

Answer

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Question 243 Marks

Give a balanced equation for the lab. Preparation of ethylene. How is the gas collected?

Answer

Balanced Equation of ethylene:
$CH _3- CH _2 OH + H _2 SO _4 \rightarrow CH _3- CH _2 HSO _4+ H _2 O $
$CH _3- CH _2 HSO _4 \xrightarrow[160^{\circ} C ]{\text { excess } H _2 SO _4} CH _2= CH _2$
The gas is collected by downward displacement of water.

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Question 253 Marks

Draw the structure of isomers of butane and write their IUPAC names.

Answer

There are two isomers are possible for butane:

1 - Butane

2 - methyl propane

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Question 263 Marks

Distinguish between the saturated hydrocarbon ethane and the unsaturated hydrocarbon ethene by drawing their structural formulae.

Answer

Ethane	Ethene

It has carbon - carbon single bond.	It has carbon - carbon double bond
It is saturated.	It is unsaturated
Alkanes undergo a substitution reaction.	Alkenes undergo addition reaction.

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Question 273 Marks

Write (a) molecular formula, (b) electron dot formula and (c) structural formula of ethene (Ethylene).

Answer

(a) The molecular formula of ethene is $C_2H_4$
(b) Electron dot formula of ethene is:

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Question 283 Marks

Name three compounds formed by ethene and give one use of each compound.

Answer

Three compounds formed by ethylene are:

Polythene
Ethanol
Epoxyethane

Uses of above compounds:

Polythene is used as carrying bags.
Ethanol is used as a starting material for other products, mainly cosmetics, and toiletry
preparation.
Epoxyethane is used in the manufacture of detergents.

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Question 293 Marks

What do you observe when ethene is passed through alkaline $KMnO_4$ solution?

Answer

When ethylene is passed through alkaline $KMnO _4$ solution 1, 2-Ethanediol is formed. The Purple color of $KMnO _4$ decolorizes.
$CH_2=CH_2+H-O-H +[O] \rightarrow CH_2(OH)-CH_2(OH)$
Cold alkaline
$KMnO_4$ solution

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Question 303 Marks

What is the substitution reaction? Give the reaction of chlorine with ethane and name the product formed?

Answer

A reaction in which one atom of a molecule is replaced by another atom (or group of atoms)is called a substitution reaction.
When ethane reacts with chlorine
$C_2H_6 +Cl_2 \rightarrow C_2H_5Cl + HCl$
Chloroethane
$C_2H_5Cl + Cl_2\rightarrow C_2H_4Cl_2+HCl$
Dichloroethane
$C_2H_4Cl_2 +Cl_2 \rightarrow C_2H_3Cl_3+HCl$
Trichloroethane
$C_2H_3Cl_3 + Cl_2 \rightarrow C_2H_2Cl_4 + HCl$
Tetrachloroethane
$C_2H_2Cl_4 +Cl_2 \rightarrow C_2HCl_5 +HCl$
Pentachloroethane
$C_2HCl_5 +Cl_2 \rightarrow C_2Cl_6 + HCl$
Hexachloroethane

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Question 313 Marks

Draw the structures of isomers of : butane. Write the IUPAC and common names of these isomer.

Answer

The structures of isomers of butane are:
(1)

Common name:- n-Butane
IUPAC name:- Butane
(2)

Common name:-iso butane
IUPAC name:- 2-methyl propane

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Question 323 Marks

Using appropriate catalysts, ethane can be oxidized to an alcohol, an aldehyde and an acid. name the alcohol, aldehyde and acid formed when ethane is oxidized.

Answer

Ethane $\rightarrow$ Alcohol
$
2 C _2 H _6+ O _2 \xrightarrow[200^{\circ} C ]{ Cu } 2 C _2 H _5 OH
$
The alcohol is ethanol.
Ethane $\rightarrow$ Aldehyde
$
C _2 H _6+ O _2 \xrightarrow[350^{\circ} C ]{ MoO } CH _3 CHO + H _2 O
$
The Aldehyde formed is ethanol.
Ethane $\rightarrow$ Acid
$
\begin{array}{c}
C _2 H _6+ O _2 \xrightarrow[350^{\circ} C ]{ MoO } CH _3 CHO + H _2 O \\
Ch _3 CHo +[ O ] \xrightarrow[\text { conc } \cdot H _2 SO _4]{ K _2 Cr _2 O _7} CH _3 COOH
\end{array}
$

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Question 333 Marks

Convert:
Methane into chloroform

Answer

Methane into chloroform
$CH_4+Cl_2 → CH_3Cl+HCl$
$CH_3Cl+Cl_2 → CH_2Cl_2+HCl$
$CH_2Cl_2+Cl_2 → CHCl_3+HCl$

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Question 343 Marks

Draw the chain isomers of hexane $(C_6H_{14}) .$

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Question 353 Marks

Define the term isomerism. State two main causes of isomerism.

Answer

Isomerism: Compounds having the same molecular formula but different structural formula
are known as isomers and the phenomenon as isomerism.
Two main causes of isomerism are:
Difference in mode of linking of atoms.
Difference in the arrangement of atoms or groups in space.

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Question 363 Marks

Draw the structural formulae of the two isomers of Butane. Give the correct IUPAC name of each of the isomer.

Answer

Structural formulae of isomers of Butane are:

Butane2-methyl propane

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Chemistry [3 Mark Question Answer]

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