Exercise 12B

Question 1

State the sources of alkanes.

Answer

Natural gas and petroleum are the principal sources of alkanes. Natural gas contains mainly
methane with smaller amounts of ethane, propane and butane.

Question 2

Methane is a greenhouse gas. Comment

Answer

Methane is a primary constituent of natural gas. It absorbs outgoing heat radiations from the
earth and thus contributes to the green house effect and so is considered as a green house gas.
Methane remains in the atmosphere for approximately 10 years. It is twenty times more
effective in trapping heat in comparison to carbon dioxide.

Question 3

Give the general formula of the alkanes.

Answer

The general formula for alkanes is CnH2n+2, where n is the number of carbon atoms.

Question 4

Draw the structures of isomers of:

(a) butane

(b) pentane

Answer

(a) Isomers of butane [C4H10]:

1. n-butane
2. Isobutane

(b) Isomers of pentane [C5H12]:

Pentane [n-pentane]

2-Methyl butane [iso-pentane]

2,2 Dimethyl Propane [neo-pentane]

Question 5

Write the :

(a) molecular formula.

(b) electron dot formula and

(c) structural formula of methane and ethane.

Answer

(a) Molecular formula

Methane - CH4

Ethane - C2H6

(b) Electron dot formula

Methane

Ethane
(c) Structural formula

Methane (CH4)

Ethane(C2H6)

Question 6

How is:

(a) methane and

(b) ethane prepared in the laboratory?

Answer

(a) Laboratory preparation of methane

A mixture of sodium ethanoate (sodium acetate) and soda lime is taken in a hard glass test
tube and heated over a bunsen flame.
CH3COONa sodium acetate+NaOHsodalime→300°CCaOCH4methane↑+Na
2CO3 sodium acetateCH3COONa+sodalimeNaOHCaO300°CmethaneCH4↑+Na2CO3
The gas evolved is collected by downward displacement of water since it is slightly soluble in
water and is lighter than air.

(b) Laboratory preparation of ethane

A mixture of sodium propionate and soda lime is taken in a boiling tube and heated over a
bunsen flame.

C2H5COONasodium propionate+NaOHsodalime→300°CCaOC2H6ethane↑
+Na2CO3sodium propionateC2H5COONa+sodalimeNaOHCaO300°CethaneC2H6↑+Na2
CO3
The gas evolved is collected by downward displacement of water.

Question 7

How are methane and ethane prepared from methyl iodide and ethyl bromide?

Answer

Iodomethane (Methyl iodide) and bromoethane (ethyl bromide) are reduced by nascent
hydrogen at ordinary room temperature.
CH3I + 2[H] ⟶ CH4 + HI

C2H5Br + 2[H] ⟶ C2H6 + HBr

Nascent hydrogen is produced by the action of Zn powder and dil. HCl or Zn/Cu couple in
alcohol.

Question 8

What is a 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.

e.g., CH4 + Cl2 ⟶ CH3Cl + HCl

Reaction of chlorine with ethane is given below:

C2H6 + Cl2 ⟶ C2H5Cl + HCl

The product formed is Monochloroetahne [C2H5Cl]

Question 9

Name the compounds formed when methane burns in:

(a) sufficient air

(b) insufficient air

Give a balanced equation.

Answer

(a) The compounds formed are carbon dioxide and water

CH4 methane+2O2[excess]⟶CO2+2H2O methaneCH4+2O2[excess]⟶CO2

+2H2O
(b) The compounds formed are carbon monoxide and water

2CH4 methane+3O2[insufficient]⟶2CO+4H2O methane2CH4+3O2

[insufficient]⟶2CO+4H2O

Question 10

Write the names and the formula of the products formed when:
(a) methane (b) ethane

reacts with (i) chlorine (ii) bromine

Write the chemical equations.

Answer

(a) Methane

(i) Reaction with chlorine: Chloromethane [CH3Cl] and Hydrochloric acid [HCl] are formed
when methane reacts with chlorine.

CH4 + Cl2 →or 600Kdiffused sunlightdiffused sunlightor 600K CH3Cl + HCl

(ii) Reaction with Bromine : Bromomethane [CH3Br] and Hydrogen bromide [HBr] are
formed when methane reacts with bromine.

CH4 + Br2 ⟶ CH3Br + HBr

(b) Ethane

(i) Reaction with chlorine: Chloroethane [C2H5Cl] and Hydrochloric acid [HCl] are formed
when ethane reacts with chlorine.

C2H6 + Cl2 ⟶ C2H5Cl + HCl

(ii) Reaction with Bromine : Bromoethane [C2H5Br] and Hydrogen bromide [HBr] are
formed when ethane reacts with bromine.

C2H6 + Br2 ⟶ C2H5Br + HBr

Question 11

Name the compound prepared from:

(a) Sodium propionate

(b) Methyl iodide and

(c) Ethyl bromide.

Write a balanced equation for the same.

Answer

(a) Sodium propionate : compound prepared are ethane and sodium carbonate

C2H5COONasodium propionate+NaOHsodalime→ΔCaOC2H6ethane↑+Na
2CO3sodium propionateC2H5COONa+sodalimeNaOHCaOΔethaneC2H6↑+Na2CO3
(b) Methyl iodide : compound prepared are methane and hydrogen iodide
CH3Imethyl iodide+2[H]nascent hydrogen→alcoholZn/Cu coupleCH4metha
ne↑+HImethyl iodideCH3I+nascent hydrogen2[H]Zn/Cu couplealcoholmethaneCH4↑+HI
(c) Ethyl bromide : compound prepared are ethane and hydrogen bromide

C2H5Brethylbromide+2[H]nascent hydrogen→alcoholZn/Cu coupleC2H6et

hane↑+HBrethylbromideC2H5Br+nascent hydrogen2[H]Zn/Cu couplealcoholethaneC2H6
↑+HBr

Question 12

Write the equation for the complete combustion of

(i) Methane

(ii) Ethane

Answer

(i) Methane:

CH4 methane+2O2[excess]⟶CO2+2H2O methaneCH4+2O2[excess]⟶CO2

+2H2O
(ii) Ethane

2C2H6 ethane+7O2[excess]⟶4CO2+6H2O ethane2C2H6+7O2

[excess]⟶4CO2+6H2O

Question 13

Convert:

(a) Methane into chloroform.

(b) Sodium acetate into methane

(c) Methyl iodide into ethane.

(d) Methane to methyl alcohol

Answer

(a) Methane into chloroform

CH4 methane+Cl2→diffused sunlightΔCH3Clmonochloromethane+HCl metha

neCH4+Cl2Δdiffused sunlightmonochloromethaneCH3Cl+HCl
nochloromethaneCH3Cl+[excess]Cl2⟶dichloromethaneCH2Cl2+HCl
CH3Clmonochloromethane+Cl2[excess]⟶CH2Cl2dichloromethane+HClmo

ldichloromethaneCH2Cl2+Cl2⟶trichloromethane or chloroformCHCl3+HCl
CH2Cl2dichloromethane+Cl2⟶CHCl3trichloromethane or chloroform+HC

(b) Sodium acetate into methane

CH3COONasodium acetate+NaOHsodalime→CaOΔCH4methane+Na2CO3s
odium acetateCH3COONa+sodalimeNaOHΔCaOmethaneCH4+Na2CO3

(c) Methyl iodide into ethane

2CH3Imethyl iodide+2Na→dry etherC2H6ethane↑+2NaImethyl iodide2CH3I

+2Nadry etherethaneC2H6↑+2NaI
(d) Methane to methyl alcohol

2CH4 methane+O2→120 atm.475 K Cu tube2CH3OHmethyl alcohol methane2

CH4+O2475 K Cu tube120 atm.methyl alcohol2CH3OH

Question 14

Give three uses of:

(a) Methane

(b) Ethane

Answer

(a) Methane

1. Methane is a source of carbon monoxide and hydrogen.

2. It is used in the preparation of useful compounds like ethyne, methanal, methanol,
chloro-methane, and tetrachloro-methane.
3. It is employed as a domestic fuel.

(b) Ethane

1. It is used in the preparation of ethene, ethanol, ethanal and ethanoic acid.

2. It forms ethyl chloride, which is used to make tetraethyllead.
3. Ethane is also a good fuel.

Question 15

Under what conditions does ethane get converted to:

(a) ethyl alcohol

(b) acetaldehyde

(c) acetic acid

Answer

(a) Ethyl alcohol — is produced when ethane and oxygen react at 120 atm pressure, 475 K
temperature and pushed through copper tubes.

2C2H6 ethane+O2→120 atm.Cu tube 475 K2C2H5OHethyl alcohol ethane2C2

H6+O2Cu tube 475 K120 atm.ethyl alcohol2C2H5OH
(b) Acetaldehyde — is produced when ethane and oxygen react by using catalyst MoO

C2H6 ethane+O2→MoOCH3CHOacetaldehyde+H2O ethaneC2H6+O2MoO

acetaldehydeCH3CHO+H2O

(c) Acetic acid

2C2H6 ethane+O2→120 atm.Cu tube 475 K2C2H5OHethyl alcohol ethane2C2

H6+O2Cu tube 475 K120 atm.ethyl alcohol2C2H5OH
C2H5OHethyl alcohol+O2→Pt. 300°CCH3COOH+H2Oacetic acidethyl alcohol
C2H5OH+O2Pt. 300°Cacetic acidCH3COOH+H2O

Question 16

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

Answer

Alcohol ⟶ Ethyl alcohol [C2H5OH]

Aldehyde ⟶ Acetaldehyde [CH3CHO]

Acid ⟶ Acetic acid [CH3COOH]

Ethane to an alcohol :

2C2H6 ethane+O2→120 atm.Cu tube 475 K2C2H5OHethyl alcohol ethane2C2

H6+O2Cu tube 475 K120 atm.ethyl alcohol2C2H5OH
Ethane to an aldehyde :

C2H6 ethane+O2→MoOCH3CHOacetaldehyde+H2O ethaneC2H6+O2MoO

acetaldehydeCH3CHO+H2O

Ethane to an acid :
2C2H6 ethane+O2→120 atm.Cu tube 475 K2C2H5OHethyl alcohol ethane2C2
H6+O2Cu tube 475 K120 atm.ethyl alcohol2C2H5OH
C2H5OHethyl alcohol+O2→Pt. 300°CCH3COOH+H2Oacetic acidethyl alcohol
C2H5OH+O2Pt. 300°Cacetic acidCH3COOH+H2O

Exercise 12C

Question 1

Write:

(a) molecular formula

(b) electron dot formula and

(c) structural formula of ethene (ethylene).

Answer

(a) C2H4

(b) Electron dot formula of ethene:

(c) Structural formula of ethene:

Question 2

The molecules of alkene family are represented by a general formula CnH2n.

Answer the following:

(a) What do n and 2n signify?

(b) What is the name of alkene when n=4?

(c) What is the molecular formula of alkene when n=4?

(d) What is the molecular formula of the alkene if there are ten H atoms in it?

(e) What is the structural formula of the third member of the alkene family?

(f) Write the molecular formula of lower and higher homologous of an alkene which contains
four carbon atoms.

Answer

(a) n is the number of carbon atoms in the molecule and 2n is the number of hydrogen atoms.

(b) Butene

(c) When n=4 then no. of carbon atoms is n=4 and hydrogen atoms is 2n=8, hence alkene
is C4H8

(d) When 2n=10 then no. of carbon atoms is n=5 and hydrogen atoms is 2n=10, hence alkene
is C5H10

(e) Third member of the alkene family is Butene. Its structural formula is shown below:

(f) Lower homologous: C3H6

Higher homologues : C5H10

Question 3(a)

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

Answer

Structural formula of Ethane [saturated]:

Structural formula of Ethene [unsaturated]:

Question 3(b)

Draw the structures of isomers of butene and write their IUPAC names.

Answer

Butene has three isomers:

But−1−ene — CH3-CH2-CH=CH2

But−2−ene — CH3-CH=CH-CH3
2-methyl-prop-1-ene — CH2=C(CH3)-CH3

Question 4

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

Answer

C2H5OH ethyl alcohol→170°CConc. H2SO4[excess]C2H4ethylene+H2O et

hyl alcoholC2H5OHConc. H2SO4[excess]170°CethyleneC2H4+H2O

The gas is collected by downward displacement of water.

Question 5

How is ethene prepared by:

(a) dehydrohalogenation reaction?

(b) dehydration reaction?

Give equations and name the products formed.

Answer

(a) Dehydrohalogenation involves elimination of hydrogen halide.

C2H5Br Bromo ethane [ethyl bromide]+KOHalcoholic, hot and conc
.⟶C2H4ethene [ethylene]+KBr Potassium bromide+H2O Bromo ethane [ethyl bro
mide]C2H5Br+alcoholic, hot and conc.KOH⟶ethene [ethylene]C2H4+ Potassium bromideKBr
+H2O
The products formed are ethene, potassium bromide and water.

(b) Dehydration involves elimination of elements of water from alcohol. Conc. sulphuric acid
act as dehydrating agent.

C2H5OH ethyl alcohol→170°CConc. H2SO4[excess]C2H4ethene+H2O ethyl

alcoholC2H5OHConc. H2SO4[excess]170°CetheneC2H4+H2O

The products formed are ethene and water.

Question 6

(a) Ethene when reacts with halogens (chlorine and bromine) form saturated products. Name
them and write balanced equations.

(b) Give the conditions and the main product formed by hydrogenation of ethene.

Answer

(a)

C2H4 ethene+Cl2→[inert solvent]CCl4C2H4Cl21,2, dichloroethane [ethylen

e chloride] etheneC2H4+Cl2CCl4[inert solvent]1,2, dichloroethane [ethylene chloride]C2H4Cl2
Product formed is 1,2, dichloroethane [ethylene chloride]

C2H4 ethene+Br2→[inert solvent]CCl4C2H4Br21,2, dibromooethane [ethyl

ene bromide] etheneC2H4+Br2CCl4[inert solvent]1,2, dibromooethane [ethylene bromide]C2H4Br2
Product formed is 1,2, dibromooethane [ethylene bromide]

(b) Conditions for hydrogenation of ethene : finely divided catalyst, such as platinum or
palladium at ordinary temperature or nickel at 200°C. Main product formed is ethane.

C2H4 ethene+H2→200°CNickleC2H6ethane etheneC2H4+H2Nickle200°CethaneC2

H6

Question 7

Convert ethanol into ethene using:

(a) solid dehydrating agent

(b) hot conc. H2SO4?

Give only balanced equations.

Answer

(a) Using Al2O3 as dehydrating agent.

C2H5OH ethyl alcohol→350°CAl2O3C2H4ethene+H2O ethyl alcoholC2H5OH

Al2O3350°CetheneC2H4+H2O

(b) Using hot conc. H2SO4

C2H5OH ethyl alcohol→170°CConc. H2SO4[excess]C2H4ethene+H2O ethyl

alcoholC2H5OHConc. H2SO4[excess]170°CetheneC2H4+H2O

Question 8

Write the following properties of ethene:

(a) Physical state

(b) Odour

(c) Density as compared to air

(d) Solubility

Answer

(a) Colourless and inflammable gas.

(b) Faint sweetish odour.

(c) Slightly less dense than air.

(d) Sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and
chloroform.

Question 9

How would you convert:

(a) ethyl bromide into ethene

(b) ethene into 1,2-dibromoethane

(c) ethene into ethane

Answer

(a) ethyl bromide into ethene : Dehydrohalogenation

C2H5Br Bromo ethane [ethyl bromide]+KOHalcoholic, hot and conc
.⟶C2H4ethene [ethylene]+KBr+H2O Bromo ethane [ethyl bromide]C2H5Br+alcoholic,
hot and conc.KOH⟶ethene [ethylene]C2H4+KBr+H2O

(b) ethene into 1,2-dibromoethane : Halogenation

C2H4 ethene+Br2→[inert solvent]CCl4C2H4Br21,2, dibromooethane [ethyl

ene bromide] etheneC2H4+Br2CCl4[inert solvent]1,2, dibromooethane [ethylene bromide]C2H4Br2
(c) ethene into ethane : Hydrogenation

H2C=CH2 ethene [ethylene]+H2→200°CNickleC2H6ethane ethene [ethylene]H2

C=CH2+H2Nickle200°CethaneC2H6

Question 10

Give balanced equations when:

(a) ethene is burnt in excess of oxygen.

(b) ethene reacts with chlorine gas.

(c) ethene combines with hydrogen chloride.

(d) a mixture of ethene and hydrogen is passed over nickel at 200°C.

Answer

(a) ethene is burnt in excess of oxygen.

C2H4 + 3O2 ⟶ 2CO2 + 2H2O + heat

(b) ethene reacts with chlorine gas.

C2H4 ethene+Cl2→[inert solvent]CCl4C2H4Cl21,2, dichloroethane [ethylen

e chloride] etheneC2H4+Cl2CCl4[inert solvent]1,2, dichloroethane [ethylene chloride]C2H4Cl2
(c) ethene combines with hydrogen chloride.

H2C=CH2 ethene [ethylene]+HCl (aq.)⟶CH3CH2Clchloroethane ethene [ethyl

ene]H2C=CH2+HCl (aq.)⟶chloroethaneCH3CH2Cl

(d) a mixture of ethene and hydrogen is passed over nickel at 200°C.

H2C=CH2 ethene [ethylene]+H2→200°CNickleC2H6ethane ethene [ethylene]H2

C=CH2+H2Nickle200°CethaneC2H6

Question 11
Give the formula and names of A, B, C and D in the following equations:

(a)

CH4→-HClCl2A→-HClCl2B→-HClCl2C→-HClCl2DCH4Cl2-HClACl2-HClBCl2
-HClCCl2-HClD

(b)
C2H2→H2A→H2B→-HBrBr2C→-HBrBr2DC2H2H2AH2BBr2-HBrCBr2-HBrD
(c)
C2H4+B→Nickle200°CC2H6C2H4+B200°CNickleC2H6
Answer

(a) A — CH3Cl (Chloro methane)

B — CH2Cl2 (Di-chloromethane)

C — CHCl3 (Tri-chloro methane)

D — CCl4 (Carbon tetrachloride)

CH4→-HClCl2CH3Cl→-HClCl2CH2Cl2→-HClCl2CHCl3→-
HClCl2CCl4CH4Cl2-HClCH3ClCl2-HClCH2Cl2Cl2-HClCHCl3Cl2-HClCCl4
(b) A — C2H4 (ethene)

B — C2H6 (ethane)

C — C2H5Br (bromo-ethane)

D — C2H4Br2 (1,2-Di-bromoethane)

C2H2→H2C2H4→H2C2H6→-HBrBr2C2H5Br→-HBrBr2C2H4Br2C2H2H2
C2H4H2C2H6Br2-HBrC2H5BrBr2-HBrC2H4Br2
(c) B — H2 (Hydrogen)

C2H4+H2→Nickle200°CC2H6C2H4+H2200°CNickleC2H6

Question 12

Write the name and formula of the product formed in each case below:

(a) C2H4 + Cl2 ⟶ ...............

(b) C2H5I + KOH (alc.) →ΔΔ ...............

(c) H2C=CH2 →alc. KMnO4alc. KMnO4 ...............

(d) H2C=CH2 + HBr ⟶...............

Answer

(a) C2H4 + Cl2 ⟶ Cl-CH2-CH2-Cl

Product formed is 1,2-dichloroethane[Cl-CH2-CH2-Cl]

(b) C2H5I + KOH (alc.) →ΔΔ C2H4 + KI + H2O

Product formed is ethene [C2H4], KI and water

(c) H2C=CH2 →alk. KMnO4alk. KMnO4 CH2(OH)-CH2(OH)

Product formed is 1,2-Ethane-diol [CH2(OH)-CH2(OH)]

(d) H2C=CH2 + HBr ⟶ C2H5Br

Product formed is Bromoethane [C2H5Br]

Question 13

What do you observe when ethene is passed through alkaline KMnO4 solution?

Answer

Ethene is oxidised with alkaline KMnO4 at room temperature, the purple colour of
KMnO4 decolourises.

H2C=CH2 ethene [ethylene]+H-O-H+[O] cold alkaline⟶OH-

⟶1,2-Ethane-diolOH-CH2−CH2OH
CH2−CH2OH1,2-Ethane-diol ethene [ethylene]H2C=CH2+ cold alkalineH-O-H+[O]

Question 14

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

Answer

1. Polythene — carry bags are made.

2. Ethanol — cosmetics and toiletries preparation.
3. Oxy-ethylene torch — used for cutting and welding of metals.

Exercise 12D

Question 1

What are the sources for alkynes? Give the general formula of alkynes.
Answer

Natural gas and petroleum are the sources of alkynes. The general formula of alkynes is :
CnH2n-2

Question 2

Give an example of isomers shown by triple bond hydrocarbons (alkynes) and write their
IUPAC names.

Answer

Isomers of Butyne exhibit position isomerism:

IUPAC name : but-1-yne

IUPAC name : but-2-yne

Question 3

How is ethyne prepared in the laboratory?

(a) Draw a diagram

(b) Give an equation

(c) How is pure dry gas collected?

Answer

(a) Below diagram shows the setup for laboratory preparation of ethyne:
(b) Ethyne [C2H2] from Calcium Carbide :

CaC2calcium carbide+2H2Owater⟶C2H2ethyne+Ca(OH)2calcium hydrox

idecalcium carbideCaC2+water2H2O⟶ethyneC2H2+calcium hydroxideCa(OH)2
(b) As the pure dry gas is insoluble in water, it is collected by downward displacement of
water.

Question 4

Give the method of preparation of ethyne by: 1,2-dibromoethane.

Answer

When 1,2-dibromoethane [ethylene dibromide] is boiled with alcoholic potassium hydroxide,

ethyne is formed.

C2H4Br2 ethylene dibromide+2KOHalcoholic→boiling200°CC2H2ethyne+

2KBr+2H2O ethylene dibromideC2H4Br2+alcoholic2KOH200°CboilingethyneC2H2
+2KBr+2H2O

Question 5

Name the hydrocarbon which:

(a) is a tetrahedral molecule.

(b) is a planar molecule.

(c) is a linear molecule.

(d) forms a red precipitate with ammoniacal solution of copper (I) chloride.

(e) is known as paraffin.

(f) is known as olefin.

(g) a compound which will give ethyne (acetylene) gas when treated with water.

Answer

(a) Methane

(b) Ethene

(c) Ethyne

(d) Ethyne

(e) Alkanes

(f) Alkenes

(g) Calcium carbide

Question 6

Classify the following compounds as alkanes, alkenes and alkynes: C3H4, C3H8, C5H8, C3H6

Answer

 Alkanes — C3H8
 Alkenes — C3H6
 Alkynes — C3H4, C5H8

Question 7

Give a chemical test to distinguish between

(a) saturated and unsaturated compounds

(b) ethane and ethene

(c) ethene (ethylene) and ethyne (acetylene)

Answer

(a) On adding few drops of alkaline potassium permanganate (purple colour) to the
hydrocarbons, no change is seen in saturated hydrocarbons whereas the purple colour fades in
case of unsaturated hydrocarbons.

(b) When bromine is passed through solutions of ethane and ethene in an inert solvent [CCl4]
at room temperature, incase of ethene gas, brown colour of bromine is discharged whereas in
case of ethane gas no change in the colour is observed.

(c) On adding ammoniacal silver nitrate, no change is seen in ethene whereas white ppt. of
silver acetylide is formed in case of ethyne.
Question 8

Compound X is bubbled through bromine dissolved in CCl4;

(a) Draw the structure of X.

(b) State your observation during the reaction.

Answer

(a) Compound 'X' is Ethene (H2C=CH2). Its structural formula is shown below:

(b) Brown colour of bromine is discharged.

Question 9

Give balanced equations for the following conversions:

(a) An alkene to an alkane

(b) An alkene to an alcohol

(c) An alkyne to an alkene.

Answer

(a) An alkene to an alkane

C2H4ethene+H2→300°CNickleC2H6ethaneetheneC2H4+H2Nickle300°CethaneC2H6
(b) An alkene to an alcohol

C2H4 ethene+H2O→300°C, 60 atm.H3PO4C2H5OHethene etheneC2H4+H2

OH3PO4300°C, 60 atm.etheneC2H5OH
(c) An alkyne to an alkene.
H2C2 ethyne [acetylene]+H2→300°CNickleC2H4ethene ethyne [acetylene]H2C2
+H2Nickle300°CetheneC2H4

Question 10

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

(a) chlorine

(b) bromine

(c) iodine

(d) hydrogen

(e) excess of hydrochloric acid.

Answer

1,2-dichloro ethene and 1,1,2,2 -tetrachloro ethane will be formed.

C2H2 + Cl2 ⟶ C2H2Cl2 + Cl2 ⟶ C2H2Cl4

(b) Bromine

1,2-dibromo ethene and 1,1,2,2 -tetrabromo ethane will be formed.

C2H2 + Br2 ⟶ C2H2Br2 + Br2 ⟶ C2H2Br4

(c) Iodine

1,2-di-iodoethene will be formed.

C2H2 + I2 ⟶ ICH=CHI

(d) Hydrogen

Ethene and then ethane will be formed.

C2H2 Ethyne+H2→NickleC2H4ethene+H2→NickleC2H6ethane EthyneC2H2

+H2NickleetheneC2H4+H2NickleethaneC2H6
(e) Excess of hydrochloric acid.

Chloro ethene and then 1,1-dichloro ethane will be formed.

C2H2 Ethyne→+ HClC2H3Clchloro ethene→+ HClC2H4Cl21,1-dichloro et

hane EthyneC2H2+ HClchloro etheneC2H3Cl+ HCl1,1-dichloro ethaneC2H4Cl2

Question 11
Substitution reactions are characteristic reactions of ............... (alkynes/alkenes/alkanes).

Answer

Substitution reactions are characteristic reactions of alkanes.

Question 12

(a) Write an equation for the laboratory preparation of

(i) An unsaturated hydrocarbon from calcium carbide.

(ii) An alcohol from ethyl bromide.

(b) What would you see, when ethyne is bubbled through a solution of bromine in carbon
tetrachloride?

(c) Name the addition product formed between ethene and water.

Answer

(a) (i) Ethyne [C2H2] from Calcium Carbide :

CaC2calcium carbide+2H2Owater⟶C2H2ethyne↑+Ca(OH)2calcium hydro

xidecalcium carbideCaC2+water2H2O⟶ethyneC2H2↑+calcium hydroxideCa(OH)2
(ii) An alcohol from ethyl bromide.

C2H5-Br Bromoethane [ethyl bromide]+KOH [aq.]→boilC2H5OH ethyl alc

ohol+KBr Bromoethane [ethyl bromide]C2H5-Br+KOH [aq.]boil ethyl alcoholC2H5OH
+KBr
(b) Brown colour of bromine disappears when ethyne is bubbled through a solution of
bromine in carbon tetrachloride.

C2H2 + Br2 ⟶ C2H2Br2 + Br2 ⟶ C2H2Br4

(c) Ethanol (C2H5OH)

C2H4 + H2O ⟶ C2H5OH

Question 13

Give reasons:

(a) Ethyne is more reactive than ethene.

(b) Ethene is more reactive than ethane.

(c) Hydrocarbons are excellent fuels.

Answer

(a) The two carbon atoms of ethyne form a triple covalent bond whereas that of ethene form a
double covalent bond. Hence, there are more electrons available in case of ethyne making it
more reactive than ethene.

(b) Ethene is an unsaturated hydrocarbon having two carbon atoms forming a double covalent
bond as their valencies are not fully satisfied by hydrogen atoms whereas ethane is a
saturated hydrocarbon as all the four valencies of its two carbon atoms are satisfied by the
hydrogen atoms. The availability of electrons in the double bond in case of ethene makes it
more reactive than ethane which has does not have electrons available in the single covalent
bond.

(c) Hydrocarbons have high calorific value. They are easily combustible and the reaction is
exothermic releasing heat energy. Hence, they are excellent fuels.

Question 14

(a) Write the balanced equations:

(i) when butane is burnt in oxygen

(ii) preparation of ethylene from ethyl alcohol.

(b) (i) Convert ethane to acetic acid

(ii) Convert ethyne to ethane.

Answer

(i) C4H10 + 6O2 ⟶ 4CO2 + 5H2O

(ii)

C2H5OH ethyl alcohol→170°CConc. H2SO4[excess]C2H4ethylene+H2O et

hyl alcoholC2H5OHConc. H2SO4[excess]170°CethyleneC2H4+H2O

(b) (i) Convert ethane to acetic acid

2C2H6 ethane+O2→120 atm.Cu tube 475 K2C2H5OHethyl alcohol ethane2C2

H6+O2Cu tube 475 K120 atm.ethyl alcohol2C2H5OH
C2H5OHethyl alcohol+O2→Pt. 300°CCH3COOH+H2Oacetic acidethyl alcohol
C2H5OH+O2Pt. 300°Cacetic acidCH3COOH+H2O
(ii) Convert ethyne to ethane.

C2H2 Ethyne+H2→NickleC2H4ethene+H2→NickleC2H6ethane EthyneC2H2

+H2NickleetheneC2H4+H2NickleethaneC2H6
Question 15

(a) Write the equation for the preparation of carbon tetrachloride from methane.

(b) Draw the structural formula of ethyne.

(c) How is the structure of alkynes different from that of alkenes?

Answer

(a) Carbon tetrachloride from methane

CH4 methane+Cl2→or 600Kdiffused sunlightCH3Cl+HCl methaneCH4+Cl2

diffused sunlightor 600KCH3Cl+HCl

Cl+Cl2⟶dichloromethaneCH2Cl2+HCl
CH3Cl chloromethane+Cl2⟶CH2Cl2dichloromethane+HCl chloromethaneCH3

H2Cl2+Cl2⟶trichloromethaneCHCl3+HCl
CH2Cl2dichloromethane+Cl2⟶CHCl3trichloromethane+HCldichloromethaneC

HCl3+Cl2⟶tetrachloromethaneCCl4+HCl
CHCl3trichloromethane+Cl2⟶CCl4tetrachloromethane+HCltrichloromethaneC

(b) Structural formula of ethyne is shown below:

(c) Alkynes contain triple bonds while alkenes contain double bonds.

Exercise 12E

Question 1

(a) What are alcohols? State their sources.

(b) Give general formulae of monohydric alcohol.

Answer

(a) Alcohols are the hydroxyl derivatives of alkane. They are formed by replacing one or
more hydrogen atoms of the alkane with an OH group.

Alcohols are not found naturally in the earth's atmosphere, they are obtained by artificial
synthesis in the laboratory.

For example, Methanol (wood spirit) is obtained from destructive distillation of wood, while
ethanol is obtained from fermentation of sugar.

(b) CnH2n+1OH
Question 2

Give the:

(a) dot diagram of first member of alcohol.

(b) abbreviated formula of third member of alcohol.

(c) structure of second member of the alcohol group.

(d) structure of alcohol with 4 carbon atoms.

Answer

(a) Methyl alcohol (CH3OH) is the first member of alcohol. Its electron dot structure is shown
below:

(b) Propyl alcohol : CH3-CH2-CH2-OH

(c) Ethyl alcohol : CH3-CH2-OH

(d) Butyl alcohol : CH3-CH2-CH2-CH2-OH

Question 3
State the method of preparation of ethanol:

(a) by hydrolysis of ethene.

(b) by hydrolysis of ethyl bromide.

Answer

(a) Hydrolysis of ethene — Ethanol is produced when ethene is heated with water at 300°C
and 60 atmosphere pressure in presence of phosphoric acid (catalyst).

C2H4 ethene+H2O→300°C, 60 atm.H3PO4C2H5OHethanol etheneC2H4+H2

OH3PO4300°C, 60 atm.ethanolC2H5OH
(b) Hydrolysis of ethyl bromide — Ethanol can be prepared by boiling aq. NaOH with ethyl
bromide.

C2H5-Br Bromoethane [ethyl bromide]+NaOH aqueous→boilC2H5OHethan

ol+NaBr Bromoethane [ethyl bromide]C2H5-Br+ aqueousNaOHboilethanolC2H5OH+NaBr

Question 4

Halo alkanes reacts with alkalies to produce alcohol. Give the equation for the preparation of
second member of homologous series of alcohol. State under what condition the reaction
occur.

Answer

Ethyl alcohol can be prepared by hydrolysis of haloalkane on reaction with hot and dilute
alkali or when an alkyl halide is boiled with aqueous alkalis.

C2H5-Br Bromoethane [ethyl bromide]+NaOHaqueous→boilC2H5OH ethyl

alcohol+NaBr Bromoethane [ethyl bromide]C2H5-Br+aqueousNaOHboil ethyl alcoholC2H5
OH+NaBr

Question 5

(a) How do the boiling point and melting point change in the homologous series of alcohols?

(b) Name the product formed when ethanol reacts with acetic acid. Give an equation.

(c) What is the name given to this type of reaction?

Answer

(a) The boiling point and melting point increase with increasing molecular weight in the
homologous series of alcohols.

(b) Ethyl acetate is generated when ethanol combines with acetic acid.
C2H5OHethanol+CH3COOHacetic acid→ΔConc. H2SO4CH3−COO−C2H5
ethyl acetate+H2OethanolC2H5OH+acetic acidCH3COOHConc. H2SO4Δethyl acetateCH3
−COO−C2H5+H2O
(c) Esterification.

Question 6

Complete and balance the following equations. State the conditions wherever necessary.

(a) H-C≡C-H + H2 ⟶ ............... + H2 ⟶ ...............

(b) C2H4 + Br2 ⟶ ...............

(c) C2H4 + HCl ⟶ ...............

(d) CaC2+ H2O ⟶ ...............

(e) C2H2 + Br2 ⟶ ...............

(f) C2H5OH →K2Cr2O7[O][O]K2Cr2O7 ...............

Answer

(a) H-C≡C-H + H2 ⟶ H2C=CH2 + H2 ⟶ H3C-CH3

(b) C2H4 + Br2 ⟶ Br-CH2-CH2-Br

(c) C2H4 + HCl ⟶ CH3CH2Cl

(d) CaC2 + 2H2O ⟶ C2H2↑ + Ca(OH)2

(e) C2H2 + Br2 ⟶ C2H2Br2

(f) C2H5OH →K2Cr2O7[O][O]K2Cr2O7 CH3CHO

Question 7

What is the effect of ethanol on human body?

Answer

Ethanol affects the part of the brain which controls our muscular movements. It gives
temporary relief from tiredness, but it damages the liver and kidney too in excess quantities.

Question 8

How are the following obtained:

(a) absolute alcohol

(b) spurious alcohol

(c) methylated spirit

Answer

(a) Absolute alcohol — By distilling wet alcohol with benzene, absolute alcohol can be
obtained. The mixture of water and benzene distils off, leaving behind anhydrous alcohol.

(b) Spurious alcohol — It is illicit liquor made by improper distillation. It contains large
proportions of methanol in a mixture of alcohols.

It's a blend of alcohol with a lot of methanol in it. It is fatal for human consumption.

(c) Methylated spirit — Ethyl alcohol is mixed 5% methyl alcohol, a coloured dye, and
some pyridine to obtain methylated spirit.

Question 9

Name the products formed and give appropriate chemical equations for the following:

(a) Sodium reacting with ethyl alcohol.

(b) Ethanol oxidised by acidified potassium dichromate.

Answer

(a) When sodium reacts with ethyl alcohol, hydrogen is produced, and sodium ethoxide is
formed.

C2H5OH + 2Na ⟶ 2C2H5ONa + H2 ↑

(b) Ethanol is oxidised and transformed to ethanal, which is then turned to acetic acid.

C2H5OHethanol→K2Cr2O7[O]CH3CHOethanal→K2Cr2O7[O]CH3COOH
ethanoic acidethanolC2H5OH[O]K2Cr2O7ethanalCH3CHO[O]K2Cr2O7ethanoic acidCH3
COOH

Question 10

Give the trivial (common) names and the IUPAC names of the following:

(a) C3H6

(b) C2H4

(c) C2H2

(d) CH3OH

(e) C2H5OH
Answer

S. No. Formula Common name IUPAC name

a) C3H6 Propylene Propene

b) C2H4 Ethylene Ethene

c) C2H2 Acetylene Ethyne

d) CH3OH Methyl alcohol Methanol

e) C2H5OH Ethyl alcohol Ethanol

Question 11

Ethanol can be oxidised to ethanoic acid. Write the equation and name the oxidising agent.

Answer

Ethanol under high pressure and low temperature when treated with oxidising agent like
acidified potassium dichromate produces ethanoic acid

C2H5OH ethanol[ethyl alcohol]→K2Cr2O7[O]CH3CHOethanal [acetaldehy

de] →K2Cr2O7[O]CH3COOHethanoic acid[acetic acid] ethanol[ethyl alcohol]C2H5
OH[O]K2Cr2O7ethanal [acetaldehyde] CH3CHO[O]K2Cr2O7ethanoic acid[acetic acid]CH3COOH

Question 12

Name an organic compound which is:

(a) used for illuminating country houses.

(b) used for making a household plastic material.

(c) called 'wood spirit'.

(d) poisonous and contain OH group.

(e) consumed as a drink.

(f) made from water gas.

(g) solvent for gums and resins.

(h) dehydrated to produced ethene.

Answer

(a) Ethyne

(b) Ethyne

(c) Methanol

(d) Methanol

(e) Ethanol

(f) Methanol

(g) Ethanol

(h) Ethanol

Question 13

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 ............... (dehydration,

dehydrogenation).

(b) Converting ethanol into ethene requires the use of ............... (conc. HCl, conc. HNO3,
conc. H2SO4).

(c) The conversion of ethene into ethane is an example of ............... (hydration,

hydrogenation).

(d) The catalyst used in the conversion of ethene into ethane is commonly ............... (iron,
nickel, cobalt).

Answer

(a) The conversion of ethanol into ethene is an example of dehydration

(b) Converting ethanol into ethene requires the use of conc. H2SO4

(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

Question 14

Write the equations for the following lab. preparations:

(a) Ethane from sodium propionate.

(b) Ethene from iodoethane.

(c) Ethyne from calcium carbide.

(d) Methanol from iodomethane.

Answer

(a) Ethane [C2H6] from sodium propionate:

C2H5COONasodium propionate+NaOHsodalime→300°CCaOC2H6ethane+
Na2CO3sodium propionateC2H5COONa+sodalimeNaOHCaO300°CethaneC2H6+Na2CO3
(b) Ethene from iodoethane:

C2H5I iodoethane+KOHalcoholic→boilH2C=CH2ethene [ethylene]

+KI+H2O iodoethaneC2H5I+alcoholicKOHboilethene [ethylene]H2C=CH2+KI+H2O
(c) Ethyne from calcium carbide:

CaC2calcium carbide+2H2Owater⟶C2H2ethyne [acetylene]

+Ca(OH)2calcium carbideCaC2+water2H2O⟶ethyne [acetylene]C2H2+Ca(OH)2
(d) Methanol from idomethane.

CH3I+NaOH⟶CH3OH+NaICH3I+NaOH⟶CH3OH+NaI

Question 15

Name the compound prepared by each of the following reactions:

(i) C2H5COONa + NaOH ⟶

(ii) CH3I + 2H ⟶

(iii) C2H5Br + KOH (alcoholic solution)⟶

(iv) CO + 2H2 (Zinc oxide catalyst) ⟶

(v) CaC2 + 2H2O ⟶

Answer

(i) Ethane

C2H5COONasodium propionate+NaOHsodalime→300°CCaOC2H6ethane+
Na2CO3sodium propionateC2H5COONa+sodalimeNaOHCaO300°CethaneC2H6+Na2CO3
(ii) Methane

CH3Imethyl iodide+2[H]nascent hydrogen→alcoholZn/Cu coupleCH4metha

ne+HImethyl iodideCH3I+nascent hydrogen2[H]Zn/Cu couplealcoholmethaneCH4+HI
(iii) Ethene [ethylene]

C2H5Br Bromo ethane [ethyl bromide]

+KOHalcoholic→boilH2C=CH2ethene [ethylene]+KBr+H2O Bromo ethane [ethyl
bromide]C2H5Br+alcoholicKOHboilethene [ethylene]H2C=CH2+KBr+H2O

(iv) Methanol

CO+2H2→catalystZinc oxideCH3OHCO+2H2Zinc oxidecatalystCH3OH

(v) Ethyne [Acetylene]

CaC2calcium carbide+2H2Owater⟶C2H2ethyne [acetylene]

+Ca(OH)2calcium hydroxidecalcium carbideCaC2+water2H2O⟶ethyne [acetylene]C2
H2+calcium hydroxideCa(OH)2

Question 16

Write the equations for the following reactions:

(a) Calcium carbide and water.

(b) Ethene and water (steam).

(c) Bromoethane and an aqueous solution of sodium hydroxide.

Answer

(a) Water is added to calcium carbide:

CaC2calcium carbide+2H2Owater⟶C2H2ethyne [acetylene]

+Ca(OH)2calcium hydroxidecalcium carbideCaC2+water2H2O⟶ethyne [acetylene]C2
H2+calcium hydroxideCa(OH)2
(b) Ethene and water (steam).

C2H4 ethene+H2O→300°C, 60 atm.H3PO4C2H5OHethene etheneC2H4+H2

OH3PO4300°C, 60 atm.etheneC2H5OH
(c) Bromoethane and an aqueous solution of sodium hydroxide.

C2H5-Br Bromoethane [ethyl bromide]+NaOH aqueous→boilC2H5OHethan

ol+NaBr Bromoethane [ethyl bromide]C2H5-Br+ aqueousNaOHboilethanolC2H5OH+NaBr

Exercise 12F

Question 1
What are carboxylic acids? Give their general formula

Answer

An organic compound containing the carboxyl group (-COOH) is known as carboxylic acid.
These compounds possess acidic properties.

General formula : CnH2n+1COOH (or RCOOH)

Question 2

Write the names of:

(a) first three members of carboxylic acid series.

(b) three compounds which can be oxidised directly, or in stages to produce acetic acid.

Answer

(a) First three members of carboxylic acid series are:

1. Methanoic acid (formic acid)

2. Ethanoic acid (acetic acid)
3. propanoic acid (propionic acid)

(b) Three compounds which can be oxidised directly, or in stages to produce acetic acid are:

1. Ethanol
2. Acetylene
3. Ethanal

Question 3

(a) Give the structural formulae of acetic acid.

(b) IUPAC name of acetic acid.

(c) What is glacial acetic acid?

Answer

(a) Structural formula of acetic acid is shown below:

(b) Ethanoic acid

(c) Acetic acid that contains a very low amount of water (less than 1%) is called anhydrous
(water-free) acetic acid or glacial acetic acid. Its melting point is around 17°C. On cooling it
forms a crystalline mass resembling ice and for this reason it is called glacial acetic acid.

Question 4

Vinegar is greyish in colour with a particular taste. Explain.

Answer

Dilute (4-5 percent) solution of ethanoic acid is also called vinegar. The presence of a
colouring matter gives vinegar a greyish colour while the presence of other organic
compounds imparts it the usual taste and flavour.

Question 5

Complete:

(a) Vinegar is prepared by the bacterial oxidation of ...............

(b) The organic acid present in vinegar is ...............

(c) The next higher homologue of ethanoic acid is ...............

Answer

(a) Vinegar is prepared by the bacterial oxidation of ethanol

(b) The organic acid present in vinegar is acetic acid

(c) The next higher homologue of ethanoic acid is propanoic acid

Question 6

How is acetic acid prepared from

(a) Ethanol

(b) Acetylene

Answer

(a) Ethanol under high pressure and low temperature when treated with oxidising agent like
acidified potassium dichromate produces ethanoic acid (acetic acid).

C2H5OH ethanol[ethyl alcohol]→K2Cr2O7[O]CH3CHOethanal [acetaldehy

de] →K2Cr2O7[O]CH3COOHethanoic acid[acetic acid] ethanol[ethyl alcohol]C2H5
OH[O]K2Cr2O7ethanal [acetaldehyde] CH3CHO[O]K2Cr2O7ethanoic acid[acetic acid]CH3COOH
(b) Acetylene is first converted to acetaldehyde by passing it through a 40 percent
H2SO4 solution at 60°C in the presence of 1% Mercury(II) Sulphate [HgSO4].
C2H2acetylene+H2O→H2SO4(dil) , HgSO4CH3CHOethanal [acetaldehyde
] acetyleneC2H2+H2OH2SO4(dil) , HgSO4ethanal [acetaldehyde] CH3CHO
The acetaldehyde is oxidised to acetic acid by passsing a mixture of acetaldehyde vapous and
air over manganese acetate at 70°C

2CH3CHOethanal [acetaldehyde] +O2→CatalystΔ2CH3COOHethanoic acid

[acetic acid]ethanal [acetaldehyde] 2CH3CHO+O2ΔCatalystethanoic acid[acetic acid]2CH3
COOH

Question 7

What do you notice when acetic acid reacts with

(a) litmus

(b) metals

(c) alkalies

(d) alcohol

Answer

(a) Acetic acid turns moist blue litmus red.

(b) Hydrogen gas with a pop sound is evolved.

2CH3COOH + Zn ⟶ (CH3COO)2Zn + H2 ↑

(c) Reacts with alkalis to form salt and water.

CH3COOH + NaOH ⟶ CH3COONa + H2O

(d) Forms an ester (pleasant fruity smelling compound) on reacting with alcohol in the
presence of dehydrating agents like concentrated sulphuric acid.

C2H5OHethyl alcohol+CH3COOH→conc. H2SO4CH3COOC2H5ethyl acet

ate+H2Oethyl alcoholC2H5OH+CH3COOHconc. H2SO4ethyl acetateCH3COOC2H5+H2
O

Question 8

Acetic acid is a typical acid. Write one equation in each case for its reaction with

(a) a metal

(b) a base/alkali

(c) a carbonate
(d) a bicarbonate

Answer

(a) a metal

2CH3COOH + Zn ⟶ (CH3COO)2Zn + H2 ↑

(b) a base/alkali

CH3COOH + NaOH ⟶ CH3COONa + H2O

(c) a carbonate

2CH3COOH + Na2CO3 ⟶ 2CH3COONa + H2O + CO2 ↑

(d) a bicarbonate

CH3COOH + NaHCO3 ⟶ CH3COONa + H2O + CO2 ↑

Question 9

What do you observe when acetic acid is added to

(a) sodium bicarbonate

(b) ethyl alcohol in the presence of sulphuric acid.

(c) neutral FeCl3 solution?

Answer

(a) Carbon dioxide is produced when acetic acid is added to sodium bicarbonate.

(b) When warmed with ethyl alcohol in the presence of sulphuric acid, a pleasant fruity smell
of ethyl acetate is produced.

(c) On adding acetic acid to neutral FeCl3 solution, wine red colour is produced.

Question 10

Name:

(a) compound formed when acetic acid and ethanol react together.

(b) reducing agent used to convert acetic acid into ethanol.

(c) substance used to change acetic acid to acetic anhydride.

Answer

(a) Ethyl acetate

(b) Lithium aluminium hydride (LiAlH4)

(c) Phosphorus pentoxide (P2O5)

Miscellaneous

Question 1(a)

(a) Which of the following statements is wrong about alkanes?

1. They are all saturated hydrocarbon.

2. They can undergo addition as well as substitution reaction.
3. They are almost non polar in nature.
4. On complete combustion give out carbon dioxide and water.

Answer

They can undergo addition as well as substitution reaction.

Reason — The non-availability of electrons in the single covalent bond makes them less
reactive and therefore undergo characteristic substitution reaction only.

Question 1(b)

The organic compound obtained as the end product of the fermentation of sugar solution is :

1. Methanol
2. Ethanol
3. Ethane
4. Methanoic acid

Answer

Ethanol

Reason —

C12H22O11cane sugar [molasses]+H2O→[yeast]invertase C6H12O6glucos

e+C6H12O6fructosecane sugar [molasses]C12H22O11+H2Oinvertase [yeast]glucoseC6H12O6
+fructoseC6H12O6
C6H12O6glucose→fermentationzymase [yeast]2C2H5OHethanol+2CO2gluco
seC6H12O6zymase [yeast]fermentationethanol2C2H5OH+2CO2

Question 1(c)

Find the odd one out and explain:

C3H8, C5H10, C2H6, CH4

Answer

C5H10

Reason — As it is not following the general alkane formula (CnH2n+2). It is an alkene with
general formula CnH2n.

Question 2

Give chemical equation for:

(a) The laboratory preparation of methane from sodium acetate.

(b) The reaction of one mole of ethene with one mole of chlorine gas.

(c) The preparation of ethyne from 1,2-dibromoethane.

Answer

(a) Methane from sodium acetate :

CH3COONasodium acetate+NaOHsodalime→CaOΔCH4methane+Na2CO3s
odium acetateCH3COONa+sodalimeNaOHΔCaOmethaneCH4+Na2CO3

(b) one mole of ethene with one mole of chlorine gas:

(c) ethyne from 1, 2 – dibromoethane.

Question 3

State how the following conversions can be carried out:

(a) Ethyl chloride to ethyl alcohol

(b) Ethyl chloride to ethene

(c) Ethene to ethyl alcohol

(d) Ethyl alcohol to ethene

Answer

(a) By boiling ethyl chloride with aqueous NaOH.

C2H5-Cl Chloroethane [ethyl chloride]+NaOH [aq.]→boilC2H5OH Ethanol

[ethyl alcohol]+NaCl Chloroethane [ethyl chloride]C2H5-Cl+NaOH [aq.]boil Ethanol [ethyl
alcohol]C2H5OH+NaCl

(b) By boiling ethyl chloride with alcoholic KOH.

C2H5-Cl Chloroethane [ethyl chloride]+KOH [aq.] alcoholic KOH→boilC2

H4 Ethene [ethylene]+KCl+H2O Chloroethane [ethyl chloride]C2H5-Cl+ alcoholic KO
HKOH [aq.]boil Ethene [ethylene]C2H4+KCl+H2O

(c) Ethene is absorbed in conc. sulphuric acid at 80 °C under 30 atmos. to give ethyl
hydrogen sulphate, which on hydrolysis with steam gives ethanol.

C2H4 Ethene+H2SO4conc.→80°C30 atmos.C2H5-HSO4 Ethyl hydrogen su

lphate EtheneC2H4+conc.H2SO430 atmos.80°C Ethyl hydrogen sulphateC2H5-HSO4

C2H5-HSO4 Ethyl hydrogen sulphate +H2Osteam⟶C2H5-OH Ethanol [eth

yl alcohol]+H2SO4 Ethyl hydrogen sulphate C2H5-HSO4+steamH2O⟶ Ethanol [ethyl alcoh
ol]C2H5-OH+H2SO4

(d) By heating ethyl alcohol with concentrated H2SO4 at 170°C.

C2H5OH ethyl alcohol→170°CConc. H2SO4[excess]C2H4ethene+H2O ethyl

alcoholC2H5OHConc. H2SO4[excess]170°CetheneC2H4+H2O

Question 4

(a) Define isomerism

(b) Give the IUPAC name of the isomer C4H10 which has a branched chain.

Answer

(a) Isomerism is the phenomenon due to which two or more compounds have the same
molecular formula but differ in molecular arrangement or in structural formula.

Example : Isomers of pentane are (i) n pentane, (ii) isopentane and (iii) neo-pentane

(b) IUPAC name of C4H10 is Butane.

Question 5
A compound X when treated with an organic acid Y (having vinegar like smell) in the
presence of the acid Z, forms a compound P which has a fruity smell.

(a) Identify X, Y and Z.

(b) Write structural formula of X and Y.

(c) What type of compound is P?

(d) Name the above reaction.

(e) If compound X and Y both have 2 carbon atoms. Write the reaction.

Answer

(a) X, Y and Z are:

X → Ethyl alcohol
Y → Acetic acid
Z → Conc. Sulphuric acid

(b) The structural formulae are shown below:

Ethyl alcohol (X)

Acetic acid (Y)

(c) Ester

(d) Esterification

(e) The reaction is given below:

C2H5OHethyl alcohol+CH3COOHacetic acid→Conc. H2SO4CH3−COO−C

2H5ethyl ethanoate+H2Oethyl alcoholC2H5OH+acetic acidCH3COOHConc. H2SO4ethyl e
thanoateCH3−COO−C2H5+H2O
Question 1a(2010)

An organic compound undergoes addition reactions and gives a red colour precipitate with
ammoniacal cuprous chloride. Therefore, the organic compound could be :

1. Ethane
2. Ethene
3. Ethyne
4. Ethanol

Answer

Ethyne

Question 1b(2010)

An organic weak acid is :

1. Formic acid
2. Sulphuric acid
3. Nitric acid
4. Hydrochloric acid

Answer

Formic acid

Question 1c(2010)

The organic compound mixed with ethanol to make it spurious is:

1. Methanol
2. Methanoic acid
3. Methanal
4. Ethanoic acid

Answer

Methanol

Question 1d(2010)

Draw the structural formula for each of the following—

(i) Ethanoic acid

(ii) But-2-yne

Answer
(i) Structural formula of Ethanoic acid is shown below:

(ii) Structural formula of But-2-yne is shown below:

Question 1e(2010)

Compound A is bubbled through bromine dissolved in carbon tetrachloride and the product
formed is CH2Br–CH2Br.

(i) Draw the structural formula of A.

(ii) What type of reaction has A undergone.

(iii) What is your observation.

(iv) Name (not formula) the compound formed when steam reacts with A in the presence of
phosphoric acid.

(v) What is the procedure for converting the product of (e) (iv) back to A ?

Answer

(i) Compound A is Ethene (H2C=CH2). It's structural formula is shown below:

(ii) Ethene [CH2=CH2] has undergone addition reaction.

(iii) Brown colour of bromine is discharged.

(iv) Ethanol
C2H4Ethene+H2O water→H+acidC2H5OH ethanolEtheneC2H4+ waterH2OacidH
+ ethanolC2H5OH

(v) Ethanol can be converted into ethene, by dehydrating it with concentrated H2SO4 at
170°C.

C2H5OH ethyl alcohol→170°CConc. H2SO4[excess]C2H4ethene+H2O ethyl

alcoholC2H5OHConc. H2SO4[excess]170°CetheneC2H4+H2O

Question 1a(2011)

The functional group present in acetic acid is:

1. Ketonic >C=O
2. Hydroxyl -OH
3. Aldehydic -CHO
4. Carboxyl -COOH

Answer

Carboxyl -COOH

Reason — Formula of acetic acid is CH3-COOH. Hence, we can see that Carboxyl -COOH is
present.

Question 1b(2011)

The unsaturated hydrocarbons undergo:

1. a substitution reaction
2. an oxidation reaction
3. an addition reaction
4. none of the above

Answer

Addition reaction

Reason — The availability of electrons in the double or triple bond makes them more
reactive and therefore they undergo characteristic addition reactions only.

Question 1c(2011)

The number of C-H bonds in ethane molecule are:

1. Four
2. Six
3. Eight
 4. Ten

Answer

Six

Reason — Below is the structural formula of Ethane:

Question 1d(2011)

Choose the correct word/phrase from within the brackets to complete the following
sentences:

(i) The catalyst used for conversion of ethene to ethane is commonly ...............
(nickel/iron/cobalt)

(ii) When acetaldehyde is oxidized with acidified potassium dichromate, it forms ...............
(ester / ethanol / acetic acid)

(iii) Ethanoic acid reacts with ethanol in the presence of concentrated H 2SO4, so as to form a
compound and water. The chemical reaction which takes place is called ...............
(dehydration/hydrogenation/esterification)

(iv) Write the equation for the reaction taking place between 1,2-dibromoethane and
alcoholic potassium hydroxide.

(v) The product formed when ethene gas reacts with water in the presence of sulphuric
acid ............... (ethanol / ethanal / ethanoic acid)

Answer

(i) The catalyst used for conversion of ethene to ethane is commonly nickel.

(ii) When acetaldehyde is oxidized with acidified potassium dichromate, it forms acetic acid.

(iii) Ethanoic acid reacts with ethanol in the presence of concentrated H 2SO4, so as to form a
compound and water. The chemical reaction which takes place is called esterification

(iv) Reaction between 1, 2 – dibromoethane and alcoholic potassium hydroxide:

(v) The product formed when ethene gas reacts with water in the presence of sulphuric acid
is ethanol.

Question 1e(2011)

Write balanced chemical equations for the following:

(i) Monochloro ethane is hydrolysed with aqueous KOH.

(ii) A mixture of sodalime and sodium acetate is heated.

(iii) Ethanol under high pressure and low temperature is treated with acidified potassium
dichromate.

(iv) Water is added to calcium carbide.

(v) Ethanol reacts with sodium at room temperature.

Answer

(i) Monochloro ethane is hydrolysed with aqueous KOH:

C2H5-Cl Chloroethane [ethyl chloride]+KOH [aq.]→boilC2H5-OH Ethanol

[ethyl alcohol]+KCl Chloroethane [ethyl chloride]C2H5-Cl+KOH [aq.]boil Ethanol [ethyl alco
hol]C2H5-OH+KCl

(ii) A mixture of sodalime and sodium acetate is heated:

CH3COONasodium acetate+NaOHsodalime→CaOΔCH4methane+Na2CO3s
odium acetateCH3COONa+sodalimeNaOHΔCaOmethaneCH4+Na2CO3

(iii) Ethanol under high pressure and low temperature is treated with acidified potassium
dichromate:

C2H5OH ethanol[ethyl alcohol]→K2Cr2O7[O]CH3CHOethanal [acetaldehy

de] →K2Cr2O7[O]CH3COOHethanoic acid[acetic acid] ethanol[ethyl alcohol]C2H5
OH[O]K2Cr2O7ethanal [acetaldehyde] CH3CHO[O]K2Cr2O7ethanoic acid[acetic acid]CH3COOH
(iv) Water is added to calcium carbide:

CaC2calcium carbide+2H2Owater⟶C2H2ethyne [acetylene]

+Ca(OH)2calcium carbideCaC2+water2H2O⟶ethyne [acetylene]C2H2+Ca(OH)2
(v) Ethanol reacts with sodium at room temperature:

2C2H5OH ethanol+2Na⟶2C2H5ONa sodium ethoxide+H2 ethanol2C2H5OH

+2Na⟶ sodium ethoxide2C2H5ONa+H2

Question 1a(2012)

(a) Give the structural formula for the following:

(i) Methanoic acid

(ii) Ethanal

(iii) Ethyne

(iv) Acetone

(v) 2-methyl propane

Answer

(i) Methanoic acid:

(ii) Ethanal:

(iii) Ethyne:

(iv) Acetone:
(v) 2-methyl propane:

Question 1b(2012)

From the following organic compounds given below, choose one compound in each case
which relates to the description [i] to [iv]:

[Ethyne, ethanol, acetic acid, ethene, methane].

(i) An unsaturated hydrocarbon used for welding purposes.

(ii) An organic compound whose functional group is carboxyl.

(iii) A hydrocarbon which on catalytic hydrogenation gives a saturated hydrocarbon.

(iv) An organic compound used as a thermometric liquid.

Answer

(i) Ethyne

(ii) Acetic acid

(iii) Ethene

(iv) Ethanol

Question 1c(2012)

(i) Why is pure acetic acid known as glacial acetic acid ?

(ii) Give a chemical equation for the reaction between ethyl alcohol and acetic acid.
Answer

(i) Acetic acid that contains a very low amount of water (less than 1%) is called anhydrous
(water-free) acetic acid or glacial acetic acid. Its melting point is around 17°C. On cooling it
forms a crystalline mass resembling ice and for this reason it is called glacial acetic acid.

(ii) Reaction between ethyl alcohol and acetic acid:

C2H5OHethyl alcohol+CH3COOHacetic acid→Conc. H2SO4CH3−COO−C

2H5ethyl acetate+H2Oethyl alcoholC2H5OH+acetic acidCH3COOHConc. H2SO4ethyl aceta
teCH3−COO−C2H5+H2O

Question 1a(2013)

(i) Give a chemical test to distinguish ethene gas and ethane gas.

(ii) Identify the statement that is incorrect about alkanes:

(A) They are hydrocarbons.

(B) There is a single covalent bond between carbon and hydrogen.

(C) They can undergo both substitution as well as addition reactions.

(D) On complete combustion they produce carbon dioxide and water.

Answer

(i) When bromine is passed through solutions of each of the gases in an inert solvent [CCl4] at
room temperature, incase of ethene gas, brown colour of bromine is discharged whereas in
case of ethane gas brown colour remains brown.

(ii) They can undergo both substitution as well as addition reactions.

Reason — The non availability of electrons in the single covalent bond makes them less
reactive and therefore alkanes undergo characteristic substitution reactions only.

Question 1b(2013)

Give the structural formula for the following:

(i) An isomer of n-butane

(ii) 2-propanol

Answer

(i) Iso-butane is an isomer of n-butane. Its structure is shown below:

(ii) 2-propanol:

Question 1a(2014)

(a) The IUPAC name of acetylene is:

(i) Propane

(ii) Propyne

(iii) ethene

(iv) ethyne

Answer

Ethyne

Question 1b(2014)

Name hydrocarbons containing -C-O||-C-||O functional group.

Answer

Ketones

Question 1c(2014)

Give preparation of ethane from sodium propionate.

Answer
Preparation of ethane from sodium propionate.

CH3-CH2.COONasodium propionate+NaOHsodalime→ΔCaOC2H6ethane+
Na2CO3sodium propionateCH3-CH2.COONa+sodalimeNaOHCaOΔethaneC2H6+Na2CO3

Question 1d(2014)

Distinguish ethane and ethene (using alkaline potassium permanganate solution).

Answer

When ethene is passed through alkaline potassium permanganate solution (cold dil. KMnO4),
it decolourizes the purple coloured solution whereas on passing Ethane, alkaline potassium
permanganate solution remains purple.

Question 1e(2014)

Give the structural formula of the following:

(i) ethanol

(ii) 1-propanal

(iii) ethanoic acid

(iv) 1,2, dichloroethane

Answer

(i) Structural formula of ethanol is shown below:

(ii) Structural formula of 1-propanal is shown below:

(iii) Structural formula of ethanoic acid is shown below:

(iv) Structural formula of 1, 2, dichloroethane is shown below:

Question 1f(2014)

Give preparation of ethanol from monochloroethane and aq. sodium hydroxide.

Answer

Preparation of ethanol from monochloroethane and aq. sodium hydroxide.

C2H5-Cl monochloroethane+NaOH[aq] aq. sodium hydroxide→boilC2H5-

OH Ethanol [ethyl alcohol]+NaCl monochloroethaneC2H5-Cl+ aq. sodium hydroxid
eNaOH[aq]boil Ethanol [ethyl alcohol]C2H5-OH+NaCl

Question 1a(2015)

(a) Give balanced chemical equations for the following conversions:

(i) Ethanoic acid to ethyl ethanoate.

(ii) Calcium carbide to ethyne

(iii) Sodium ethanoate to methane.

Answer

(i) Ethanoic acid to ethyl ethanoate. :

C2H5OHethyl alcohol+CH3COOHacetic acid→Conc. H2SO4CH3−COO−C
2H5ethyl ethanoate+H2Oethyl alcoholC2H5OH+acetic acidCH3COOHConc. H2SO4ethyl e
thanoateCH3−COO−C2H5+H2O

(ii) Ethyne is formed

CaC2calcium carbide+2H2Owater⟶C2H2ethyne [acetylene]

+Ca(OH)2calcium carbideCaC2+water2H2O⟶ethyne [acetylene]C2H2+Ca(OH)2
(iii) Sodium ethanoate to methane

CH3COONasodium acetate+NaOHsodalime→ΔCaOCH4methane+Na2CO3s
odium acetateCH3COONa+sodalimeNaOHCaOΔmethaneCH4+Na2CO3

Question 1b(2015)

Using their structural formula identify the functional group by circling them:

(i) Dimethyl ether

(ii) Propanone

Answer

(i) Dimethyl ether contains the functional group Alkoxy (ether). It is circled in its structural
formula below:

(ii) Propanone contains the functional group Keto. It is circled in its structural formula below:

Question 1c(2015)

Name the following:

(i) Process by which ethane is obtained from ethene.

(ii) A hydrocarbon which contributes towards the greenhouse effect.

(iii) Distinctive reaction that takes place when ethanol is treated with acetic acid.

(iv) The property of elements by virtue of which atoms of the element can link to each other
in the form of a long chain or ring structure.

(v) Reaction when an alkyl halide is treated with alcoholic potassium hydroxide.

Answer

(i) Catalytic hydrogenation (addition)

(ii) Methane

(iii) Esterification

(iv) Catenation

(v) Dehydrohalogenation

Question 1d(2015)

Hydrocarbon which is a greenhouse gas is:

1. Acetylene
2. Ethylene
3. Ethane
4. Methane

Answer

Methane

Reason — Methane absorbs outgoing heat radiation from the earth. It is twenty times more
effective in trapping heat in comparison to carbon dioxide. Hence, it contributes to green
house