Organic Chemistry

(a) What are organic compounds?

(b) What is vital force theory? Why was it discarded?

Answer

(a) Organic compounds are the compounds of carbon excluding oxides of carbon, metallic carbonates and related compounds like metal cyanides, metal carbides, etc.

(b) As organic compounds were obtained straight from nature and there was no known method of preparing them in the laboratory, hence it was believed that they were the products of some vital force of nature. This theory was known as vital force theory.

This theory was soon discarded when in 1828, Friedrich Wohler demonstrated that an organic chemical (urea) could be produced in the laboratory.

(a) Name a few sources of organic compounds.

(b) Give the various applications of organic chemistry.

Answer

(a) Sources of organic compounds are:

1. Plants
2. Animals
3. Coal
4. Petroleum
5. Fermentation
6. Wood
7. Synthetic methods

(b) Organic chemistry is used in the manufacturing of soaps, shampoos, powders, and perfumes. The clothes we wear, the food we eat i.e., carbohydrates, proteins, fats, vitamins etc.,fuels we use, natural gas, petroleum products, medicines, explosives, dyes, insecticides,etc., are all organic compounds. There is hardly any walk of life where we do not use organic compounds.

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

Answer

Organic chemistry is extremely useful to us in our daily life.

The soaps and shampoos we use while taking bath, the powders, perfumes, etc., we apply on the body, the clothes we wear, food we eat i.e., carbohydrates, proteins, fats, vitamins etc., fuels we use, natural gas, petroleum products, medicines, explosives, dyes, insecticides, etc., are all organic compounds. There is hardly any walk of life where we do not use organic compounds.

Carbon shows some unique properties, name them.

Answer

Unique properties of carbon are :

1. Tetravalency of carbon
2. Catenation

Explain the following:

(a) Tetravalency

(b) Catenation

Answer

(a) Tetravalency : Carbon has four valence electrons (At. no. of C = 6; Electronic Config. 2,4). Since it can neither lose nor gain electrons to attain octet, it forms covalent bonds by sharing it's four electrons with other atoms. This characteristics of the carbon atom , by virtue of which it forms four covalent bonds , is called the tetravalency of carbon.

(b) 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.

Write any four properties of organic compounds that distinguish them from inorganic compounds.

Answer

Why are organic compounds studied as a separate branch of chemistry?

Answer

The unique nature of carbon atom (catenation and tetravalency) gives rise to the formation of a large number of compounds. More than 5 million organic compounds are known today and thousand are added every year. Hence, it demands a new field of chemistry i.e., organic chemistry.

What are hydrocarbons? Compare saturated and unsaturated hydrocarbons?

Answer

Hydrocarbons are compounds that are made up of only carbon and hydrogen atoms.

Give reason for the existence of the large number of organic compounds.

Answer

Carbon shows unique properties of tetravalency and catenation. Due to this unique nature of carbon atoms, they form single, double and triple covalent bonds with other carbon atoms and a variety of other elements. Carbon atoms have the ability to form stable bonds with other atoms resulting in the formation of long chains, branched structures, and cyclic compounds. These properties of carbon atom gives rise to the formation of a large number of compounds.

Give at least one example in each case to show the structure of isomers of:

(a) Single bond compound

(b) Double bond compound

(c) Triple bond compound

Answer

(a) Single bond compound : C₄H₁₀ has two chain isomers

1. n-butane

2. Isobutane

(b) Double bond compound : C₄H₈ has two position isomers

1. But-1-ene

2. But-2-ene

(c) Triple bond compound : C₄H₆ has two position isomers

1. But-1-yne

2. But-2-yne

Name a compound of each type and draw the figure,

(a) Cyclic compound with single bond

(b) Cyclic compound with triple bond

Answer

(a) Cyclopropane [C₃H₆]

(b) Cyclopentyne [C₅H₆]

Give the name of one member of each of the following:

(a) saturated hydrocarbons

(b) unsaturated hydrocarbons

Answer

(a) Methane

(b) Ethene

Define substitution and addition reactions. Give an example for each.

Answer

Substitution reactions — 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

Addition reactions — A reaction involving addition of atoms or molecules to the double or the triple bond of an unsaturated compound so as to yield a saturated product is known as addition reaction.

e.g., C₂H₄ + Br₂ ⟶ C₂H₄Br₂

Define a functional group and give the structural formula of the following functional groups:

(a) Ketone

(b) Alcohols

(c) Aldehydes

Answer

Functional group is defined as an atom or group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds.

The structural formula of the functional groups are given below:

(a) $\overset{\underset{\text{||}}{\text{O}}}{\text{-C-}}$

(b) -OH

(c) -CH=O

Write the name and formula of fourth member of the following homologous series:

(a) Alkyne

(b) Alcohol

Answer

(a) Butyne C₄H₆

(b) Butanol C₄H₉OH

Which part of an organic compound determines

(i) Physical properties

(ii) Chemical properties

Answer

(i) Alkyl group

(ii) Functional group

Name the alkyl radical and the functional group of the following organic compounds:

(a) CH₃OH

(b) C₂H₅OH

(c) C₃H₇CHO

(d) C₄H₉COOH

(e) CH₃COOH

(f) HCHO

Answer

(a) CH₃OH

Alkyl radical — Methyl (-CH₃)

Functional group — Alcohol (-OH)

(b) C₂H₅OH

Alkyl radical — Ethyl (-C₂H₅)

Functional group — Alcohol (-OH)

(c) C₃H₇CHO

Alkyl radical — Propyl (-C₃H₇)

Functional group — Aldehyde (-CHO)

(d) C₄H₉COOH

Alkyl radical — Butyl (-C₄H₉)

Functional group — carboxyl (-COOH)

(e) CH₃COOH

Alkyl radical — Methyl (-CH₃)

Functional group — carboxyl (-COOH)

(f) HCHO

Alkyl radical — (-H)

Functional group — Aldehyde (-CHO)

(a) What is an alkyl group?

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

Answer

(a) An alkyl group of atoms is obtained by removing one atom of hydrogen from an alkane molecule.

(b) Three alkyl radicals are:

1. Methyl
2. Ethyl
3. Propyl

These are formed by losing one hydrogen atom

CH₄ ⟶ CH₃ + H

C₂H₆ ⟶ C₂H₅ + H

C₃H₈ ⟶ C₃H₇ + H

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

Answer

First three members of the homologous series of alkanes are :

1. Methane (CH₄)

2. Ethane(C₂H₆)

3. Propane (C₃H₈)

(a) What is a homologous series?

(b) What is the difference in the molecular formula of any two adjacent homologues:

1. in terms of molecular mass.
2. in terms of number and kind of atoms per molecule?

Answer

(a) A homologous series is a group of organic compounds having a similar structure and similar chemical properties in which the successive compounds differ by a CH₂ group.

(b) The difference in the molecular formula of two adjacent homologues:

1. In terms of molecular mass is 14 a.m.u.
2. In terms of number & kind of atoms per molecule is that each member of the series differs from the preceding one by the addition of CH₂ group.

Write the IUPAC name of:

Answer

2,2-Dimethylpropane

Write the IUPAC name of:

Answer

2-Methylbutane

Write the IUPAC name of:

Answer

Prop-1-ene

Write the IUPAC name of:

Answer

2,2-Dimethylpentane

Write the IUPAC name of:

Answer

Pent-2-yne

Write the IUPAC name of:

Answer

3-Methylbut-1-yne

Write the IUPAC name of:

Answer

2,3-Dichloropentane

Write the IUPAC name of:

Answer

3-Methylheptane

Write the IUPAC name of:

Answer

But-2-ene

Write the IUPAC name of:

Answer

Hept-2-yne

Write the IUPAC name of:

Answer

5,5-Dimethylhexanal

Write the IUPAC name of:

Answer

Pentan-2-ol

Write the IUPAC name of:

Answer

4-Methylpentanoic acid

Write the IUPAC name of:

Answer

2-Bromo-2-methylbutane

Write the IUPAC name of:

Answer

1-Bromo-3-methylbutane

Write the IUPAC name of:

Answer

Prop-1-yne

Write the IUPAC name of:

Answer

Methanal

Write the IUPAC name of:

Answer

Prop-1-yne

Write the IUPAC name of:

Answer

Propan-1-ol

Write the IUPAC name of:

Answer

Ethanoic acid

Write the IUPAC name of:

Answer

Ethanal

Write the IUPAC name of:

Answer

1,2-Dichloroethane

Write the structure of Prop-1-ene

Answer

Prop-1-ene

Write the structure of 2,3-dimethylbutane

Answer

2,3-dimethylbutane

Write the structure of 2-methylpropane

Answer

2-methylpropane

Write the structure of 3-hexene

Answer

3-hexene

Write the structure of Prop-1-yne

Answer

Prop-1-yne

Write the structure of 2-methylprop-1-ene.

Answer

2-methylprop-1-ene

Write the structure of Alcohol with molecular formula C₄H₁₀O

Answer

Alcohol with molecular formula C₄H₁₀O

Choose the correct answer:

C₅H₁₁ is an

1. alkane
2. alkene
3. alkyne
4. alkyl group

Answer

(a) Alkyl group

Reason — It follows the formula C_nH_{2n + 1}

Choose the correct answer:

A hydrocarbon of the general formula C_nH_2n is

1. C₁₅H₃₀
2. C₁₂H₂₆
3. C₈H₂₀
4. C₆H₁₄

Answer

C₁₅H₃₀

Reason — According to the formula C_nH_2n, hydrogen is double of carbon, hence, C₁₅H₃₀ follows the formula C_nH_2n

The total number of different carbon chains that four carbon atoms form in alkane is :

1. 5
2. 4
3. 3
4. 2

Answer

2

Reason — The chain structures are shown below:

n-butane

Isobutane

CH₃-CH₂-OH and CH₃-O-CH₃ are :

1. Position isomers
2. Chain isomers
3. Homologous
4. Functional group isomers

Answer

Functional group isomers

Reason — CH₃-CH₂-OH is ethyl alcohol and contains Hydroxyl (OH) as the functional group.

CH₃-O-CH₃ is Dimethyl ether and contains Ether C-O-C as the functional group.

As the two have same molecular formula but different but different functional groups hence, they are called functional isomers.

The IUPAC name of the compound is :

1. 3-trimethylhexane

2. 3-methyl hexane

3. 4-methyl hexane

Answer

3-methylhexane

Reason — As one methyl group is attached at the third carbon and the longest chain is of 6 carbon atoms, hence, the name is 3-methylhexane

Fill in the blanks.

(a) Propane and ethane are ............... (homologous, isomers)

(b) A saturated hydrocarbon does not participate in a/an ............... reaction (substitution, addition)

(c) Succeeding members of a homologous series differ by ............... (CH, CH₂, CH₃)

(d) As the molecular masses of hydrocarbons increase, their boiling points ............... and melting points ............... (increase, decrease)

(e) C₂₅H₅₂ and C₅₀H₁₀₂ belong to ............... homologous series (the same, different)

(f) CO is an ............... compound. (organic, inorganic)

(g) The chemical properties of an organic compound are largely decided by the ............... and the physical properties of an organic compound are largely decided by the ............... (functional group, number of carbon atoms)

(h) CHO is the functional group of an ............... (alcohol, aldehyde)

(i) The root in the IUPAC name of an organic compound depends upon the number of carbon atoms in ............... (any chain, principal chain)

(j) But-1-ene and but-2-ene are examples of ............... isomerism (chain, position, functional)

Answer

(a) Propane and ethane are homologous.

(b) A saturated hydrocarbon does not participate in a/an addition reaction.

(c) Succeeding members of homologous series differ by CH₂.

(d) As the molecular masses of hydrocarbons increase, their boiling points increase and melting points increase.

(e) C₂₅H₅₂ and C₅₀H₁₀₂ belong to the same homologous series

(f) CO is an inorganic compound.

(g) The chemical properties of an organic compound are largely decided by the functional group and the physical properties of an organic compound are largely decided by the number of carbon atom.

(h) CHO is the functional group of an aldehyde.

(i) The root in the IUPAC name of an organic compound depends upon the number of carbon atoms in principal chain.

(j) But-1-ene and but-2-ene are examples of position isomerism.

Define or explain chain isomerism and position isomerism with examples in each case.

Answer

Chain isomerism — When two or more compounds have a similar molecular formula but are different in the arrangement of carbon atoms in straight or branched chains the compounds are referred as chain isomers.

Example: Pentane C₅H₁₂

Pentane [n-pentane]

2-Methyl butane [iso-pentane]

2,2 Dimethyl Propane [neo-pentane]

Position isomers — When two or more compounds with the same molecular formula differ in the position of substituent atom or functional group on the carbon atom, they are called position isomers.

Example : But-1-yne and But-2-yne

But-1-yne

But-2-yne

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

Answer

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.

Two main causes of isomerism are:

1. Difference is the mode of linking of atoms.
2. Difference in the arrangement of atoms or groups in space.

Draw the chain isomers of hexane (C₆H₁₄).

Answer

The chain isomers of hexane are shown below:

n-hexane

2 Methylpentane

3 Methylpentane

2,3 Dimethylbutane

2,2 Dimethylbutane

Draw position isomers of butene (C₄H₈)

Answer

Position isomers of butene are shown below:

1-butene

2-butene

Draw structural formula for each of the following compounds:

(a) isomer of n-butane

(b) Vinegar

(c) 2-Propanol

(d) Ethanal

(e) Acetone

(f) Diethyl ether

What is used to describe these compounds together?

Answer

(a) isomer of n-butane is Isobutane. Its structural formula is shown below:

Isobutane

(b) Vinegar (acetic acid)

(c) 2-Propanol

(d) Ethanal

(e) Acetone

(f) Diethyl ether

These compounds together can be called organic compounds.

(a) What is the special feature of the structure of:

(i) Ethene

(ii) Ethyne

(b) What type of reaction is common to both of the above compounds? Why methane does not undergo this type of reaction.

(c) What is the IUPAC name of dimethyl ether.

Answer

(i) The special feature of the structure of ethene is that the two carbon atoms are linked by double covalent bond formed by sharing two pairs of electrons between the two carbon atoms.

(ii) The special feature of the structure of ethyne is that the two carbon atoms are linked by triple covalent bond formed by sharing three pairs of electrons between the two carbon atoms.

(b) The above compounds undergo addition reactions. Methane does not undergo this type of reaction as its all 4 valencies are satisfied by hydrogen atoms forming single bond and so they are less reactive and undergo substitution reaction only.

(c) Methoxymethane

Which type of reaction will (i) ethane and (ii) ethene undergoe?

Answer

(i) Ethane will undergo Substitution reactions.
Reason — In case of ethane, all of its 4 valencies are satisfied by hydrogen atoms forming single bond and so they are less reactive and undergo substitution reaction only.

(ii) Ethene will undergo Addition reactions.
Reason — In case of ethene, the valencies of atleast 2 carbon atoms are not fully satisfied by hydrogen atoms. The availability of electrons in the double bond makes them more reactive and hence they undergo addition reactions only.

Choosing only words from the following list, write down appropriate words to fill in the blanks from (a) to (e) given below.

Addition, carbohydrates, C_nH_2n-2, C_nH_2n, C_nH_2n+2, electrochemical, homologous, hydrocarbon, saturated, substitution, unsaturated.

The alkanes form an (a) ............... series with the general formula (b) ............... The alkanes are (c) ............... (d) ............... which generally undergo (e) ............... reactions.

Answer

The alkanes form a (a) homologous series with the general formula (b) C_nH_2n+2. The alkanes are (c) saturated (d) hydrocarbons which generally undergo (e) substitution reactions.

Draw the structural formula of a compound with two carbon atoms in each of the following cases.

(a) An alkane with a carbon to carbon single bond.

(b) An alcohol containing two carbon atoms.

(c) An unsaturated hydrocarbon with a carbon to carbon triple bond.

Answer

(a) Ethane : CH₃-CH₃

(b) Ethanol : C₂H₅OH

(c) Ethyne : C₂H₂

Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol.

From the above, name

(a) The compound with -OH as the part of it's structure.

(b) The compound with -COOH as the part of its structure.

(C) Homologue of homologous series with general formula C_nH_2n.

Answer

(a) Ethanol

(b) Ethanoic acid

(c) Ethene

Give the correct IUPAC name and the functional group for each of the compounds whose structural formulae are given below:

Answer

(a) IUPAC name: Propanoic acid

Functional group: -COOH

(b) IUPAC name: Propanol

Functional group: -OH

Copy and complete the following table which relates to three homologous series of hydrocarbons:

Answer

Fill in the blanks with the correct words from the brackets:

(a) Alkenes are the (i) ............... (analogous/homologous) series of (ii) ............... (saturated/unsaturated) hydrocarbons. They differ from alkanes due to the presence of (iii) ............... (double/single) bonds. Alkenes mainly undergo (iv) ............... (addition/substitution) reactions.

(b) The organic compound which undergoes substitution reaction is (v) ............... (C₂H₂, C₂H₄, C₁₀H₁₈, C₂H₆)

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

Answer

(a) Alkenes are the (i) homologous series of (ii) unsaturated hydrocarbons. They differ from alkanes due to the presence of (iii) double bonds. Alkenes mainly undergo (iv) addition reactions.

(b) The organic compound which undergoes substitution reaction is (v) C₂H₆.

(c) The correct IUPAC names of isomers of Butane are Butane and 2-Methyl propane. Their structural formulae are given below:

1. Butane [n-butane]

2. 2-Methyl propane [iso-butane]

Name:

(a) The saturated hydrocarbon containing two carbon atoms.

(b) An alcohol with three carbon atom.

(c) A triple bond hydrocarbon with two carbon atoms.

Answer

(a) Ethane [C₂H₆]

(b) Propan-1-ol [C₃H₇OH]

(c) Ethyne [C₂H₄]

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.

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.

Give the general formula of the alkanes.

Answer

The general formula for alkanes is C_nH_2n+2, where n is the number of carbon atoms.

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]

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)

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.

$\underset{\text{ sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{methane}}{\text{C}\text{H}_4}↑ + \text{Na}_2\text{CO}_3$

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.

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + \text{Na}_2\text{CO}_3$

The gas evolved is collected by downward displacement of water.

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.

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]

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

$\underset{\text{ methane} }{\text{CH}_4} + 2\text{O}_2\text{[excess]} \longrightarrow \text{CO}_2 + 2\text{H}_2\text{O}$

(b) The compounds formed are carbon monoxide and water

$\underset{\text{ methane} }{\text{2CH}_4} + 3\text{O}_2\text{[insufficient]} \longrightarrow \text{2CO} + 4\text{H}_2\text{O}$

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 $\xrightarrow[\text{or 600K}]{\text{diffused sunlight}}$ 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

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

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[\Delta]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + \text{Na}_2\text{CO}_3$

(b) Methyl iodide : compound prepared are methane and hydrogen iodide

$\underset{\text{methyl iodide}}{\text{CH}_3\text{I}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{methane}}{\text{CH}_4} ↑ +\text{HI}$

(c) Ethyl bromide : compound prepared are ethane and hydrogen bromide

$\underset{\text{ethylbromide}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑+\text{HBr}$

Write the equation for the complete combustion of

(i) Methane

(ii) Ethane

Answer

(i) Methane:

$\underset{\text{ methane} }{\text{CH}_4} + 2\text{O}_2\text{[excess]} \longrightarrow \text{CO}_2 + 2\text{H}_2\text{O}$

(ii) Ethane

$\underset{\text{ ethane} }{2\text{C}_2\text{H}_6} + 7\text{O}_2\text{[excess]} \longrightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}$

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

$\underset{\text{ methane} }{\text{CH}_4} + \text{Cl}_2 \underset{\Delta}{\xrightarrow{\text{diffused sunlight}}} \underset{\text{monochloromethane}}{\text{CH}_3\text{Cl}} + \text{HCl}$

$\underset{\text{monochloromethane}}{\text{CH}_3\text{Cl}} + \underset{\text{[excess]}}{\text{Cl}_2} \longrightarrow \underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{HCl}$

$\underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{Cl}_2 \longrightarrow \underset{\text{trichloromethane or chloroform}}{\text{CHCl}_3}+ \text{HCl}$

(b) Sodium acetate into methane

$\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3$

(c) Methyl iodide into ethane

$\underset{\text{methyl iodide}}{2\text{CH}_3\text{I}} + 2\text{Na} \xrightarrow{\text{dry ether}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} ↑ + 2\text{NaI}$

(d) Methane to methyl alcohol

$\underset{\text{ methane}}{2\text{CH}_4} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{475 K Cu tube}} \underset{\text{methyl alcohol}}{2\text{CH}_3\text{OH}}$

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.

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.

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

(b) Acetaldehyde — is produced when ethane and oxygen react by using catalyst MoO

$\underset{\text{ ethane}}{\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow{\text{MoO}} \underset{\text{acetaldehyde} }{\text{CH}_3\text{CHO}} + \text{H}_2\text{O}$

(c) Acetic acid

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}$

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 :

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

Ethane to an aldehyde :

$\underset{\text{ ethane}}{\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow{\text{MoO}} \underset{\text{acetaldehyde} }{\text{CH}_3\text{CHO}} + \text{H}_2\text{O}$

Ethane to an acid :

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}$

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:

The molecules of alkene family are represented by a general formula C_nH_2n.

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

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]:

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

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

Answer

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethylene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

The gas is collected by downward displacement of water.

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.

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}_2\text{H}_4} + \underset{\text{ Potassium bromide}}{\text{KBr}} + \text{H}_2\text{O}$

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.

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

The products formed are ethene and water.

(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)

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Cl}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dichloroethane [ethylene chloride]}}{\text{C}_2\text{H}_4\text{Cl}_2}$

Product formed is 1,2, dichloroethane [ethylene chloride]

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Br}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dibromooethane [ethylene bromide]}}{\text{C}_2\text{H}_4\text{Br}_2}$

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.

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

Convert ethanol into ethene using:

(a) solid dehydrating agent

(b) hot conc. H₂SO₄?

Give only balanced equations.

Answer

(a) Using Al₂O₃ as dehydrating agent.

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[350\degree\text{C}]{\text{Al}_2\text{O}_3} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

(b) Using hot conc. H₂SO₄

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

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.

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

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}_2\text{H}_4} + \text{KBr} + \text{H}_2\text{O}$

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

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Br}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dibromooethane [ethylene bromide]}}{\text{C}_2\text{H}_4\text{Br}_2}$

(c) ethene into ethane : Hydrogenation

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

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.

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{Cl}_2 \xrightarrow[\text{[inert solvent]}]{\text{CCl}_4} \underset{\text{1,2, dichloroethane [ethylene chloride]}}{\text{C}_2\text{H}_4\text{Cl}_2}$

(c) ethene combines with hydrogen chloride.

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{HCl (aq.)}\longrightarrow \underset{\text{chloroethane}}{\text{CH}_3\text{CH}_2\text{Cl}}$

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

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{H}_2 \xrightarrow[200\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

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

(a)

$\text{CH}_4 \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{A} \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{B}\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{C}\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{D}$

(b)
$\text{C}_2\text{H}_2 \xrightarrow{\text{H}_2} \text{A} \xrightarrow{\text{H}_2} \text{B}\xrightarrow[\text{-HBr}]{\text{Br}_2} \text{C}\xrightarrow[\text{-HBr}]{\text{Br}_2} \text{D}$

(c)
$\text{C}_2\text{H}_4 + \text{B} \xrightarrow[\text{Nickle}]{200\degree\text{C}} \text{C}_2\text{H}_6$

Answer

(a) A — CH₃Cl (Chloro methane)

B — CH₂Cl₂ (Di-chloromethane)

C — CHCl₃ (Tri-chloro methane)

D — CCl₄ (Carbon tetrachloride)

$\text{CH}_4 \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CH}_3\text{Cl} \xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CH}_2\text{Cl}_2\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CH}\text{Cl}_3\xrightarrow[\text{-HCl}]{\text{Cl}_2} \text{CCl}_4$

(b) A — C₂H₄ (ethene)

B — C₂H₆ (ethane)

C — C₂H₅Br (bromo-ethane)

D — C₂H₄Br₂ (1,2-Di-bromoethane)

$\text{C}_2\text{H}_2 \xrightarrow{\text{H}_2} \text{C}_2\text{H}_4 \xrightarrow{\text{H}_2} \text{C}_2\text{H}_6 \xrightarrow[\text{-HBr}]{\text{Br}_2} \text{C}_2\text{H}_5\text{Br}\xrightarrow[\text{-HBr}]{\text{Br}_2} \text{C}_2\text{H}_4\text{Br}_2$

(c) B — H₂ (Hydrogen)

$\text{C}_2\text{H}_4 + \text{H}_2 \xrightarrow[\text{Nickle}]{200\degree\text{C}} \text{C}_2\text{H}_6$

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

(a) C₂H₄ + Cl₂ ⟶ ...............

(b) C₂H₅I + KOH (alc.) $\xrightarrow{\Delta}$ ...............

(c) H₂C=CH₂ $\xrightarrow{\text{alc. KMnO}_4}$ ...............

(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.) $\xrightarrow{\Delta}$ C₂H₄ + KI + H₂O

Product formed is ethene [C₂H₄], KI and water

(c) H₂C=CH₂ $\xrightarrow{\text{alk. KMnO}_4}$ 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]

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.

$\underset{\text{ ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \underset{\text{ cold alkaline}}{\text{H-O-H} + \text{[O]}} \longrightarrow \underset{\text{1,2-Ethane-diol}}{\text{OH-CH}_2-\text{CH}_2\text{OH}}$

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.

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 : C_nH_2n-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

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 :

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(b) As the pure dry gas is insoluble in water, it is collected by downward displacement of water.

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.

$\underset{\text{ ethylene dibromide}}{\text{C}_2\text{H}_4\text{Br}_2} + \underset{\text{alcoholic}}{\text{2KOH}} \xrightarrow[\text{boiling}]{\text{200}\degree \text{C}} \underset{\text{ethyne}}{\text{C}_2\text{H}_2} + 2\text{KBr} + 2\text{H}_2\text{O}$

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

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

Answer

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

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.

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.

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

$\underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(b) An alkene to an alcohol

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethene}}{\text{C}_2\text{H}_5\text{OH}}$

(c) An alkyne to an alkene.

$\underset{\text{ ethyne [acetylene]}}{\text{H}_2\text{C}_2} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4}$

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.

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(e) Excess of hydrochloric acid.

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

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} \xrightarrow{\text{+ HCl}} \underset{\text{chloro ethene}}{\text{C}_2\text{H}_3\text{Cl}} \xrightarrow{\text{+ HCl}} \underset{\text{1,1-dichloro ethane}}{\text{C}_2\text{H}_4\text{Cl}_2}$

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

Answer

Substitution reactions are characteristic reactions of alkanes.

(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 :

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne}}{\text{C}_2\text{H}_2} ↑ + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(ii) An alcohol from ethyl bromide.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \text{KOH [aq.]} \xrightarrow{\text{boil}} \underset{ \text{ ethyl alcohol}} {\text{C}_2\text{H}_5\text{OH}} + \text{KBr}$

(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

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.

(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)

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethylene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

(b) (i) Convert ethane to acetic acid

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[120 \text{ atm.}]{\text{Cu tube 475 K}} \underset{\text{ethyl alcohol}}{2\text{C}_2\text{H}_5\text{OH}}$

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{O}_2 \xrightarrow{\text{Pt. 300}\degree\text{C}} \underset{\text{acetic acid}}{\text{CH}_3\text{COOH} + \text{H}_2\text{O}}$

(ii) Convert ethyne to ethane.

$\underset{\text{ Ethyne}}{\text{C}_2\text{H}_2} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

(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

$\underset{\text{ methane} }{\text{CH}_4} + \text{Cl}_2 \xrightarrow[\text{or 600K}]{\text{diffused sunlight}} \text{CH}_3\text{Cl} + \text{HCl}$

$\underset{\text{ chloromethane} }{\text{CH}_3\text{Cl}} + \text{Cl}_2 \longrightarrow \underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2}+ \text{HCl}$

$\underset{\text{dichloromethane}}{\text{CH}_2\text{Cl}_2} + \text{Cl}_2 \longrightarrow \underset{\text{trichloromethane}}{\text{CH}\text{Cl}_3}+ \text{HCl}$

$\underset{\text{trichloromethane}}{\text{CHCl}_3} + \text{Cl}_2 \longrightarrow \underset{\text{tetrachloromethane}}{\text{CCl}_4}+ \text{HCl}$

(b) Structural formula of ethyne is shown below:

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

(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) C_nH_2n+1OH

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

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).

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethanol}}{\text{C}_2\text{H}_5\text{OH}}$

(b) Hydrolysis of ethyl bromide — Ethanol can be prepared by boiling aq. NaOH with ethyl bromide.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{ aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ethanol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}$

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.

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ ethyl alcohol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}$

(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.

$\underset{\text{ethanol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow[\Delta]{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl acetate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}$

(c) Esterification.

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 $\xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}}$ ...............

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 $\xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}}$ CH₃CHO

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.

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.

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.

$\underset{ \text{ethanol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal}}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanoic acid}}{\text{CH}_3\text{COOH}}$

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

(a) C₃H₆

(b) C₂H₄

(c) C₂H₂

(d) CH₃OH

(e) C₂H₅OH

Answer

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

$\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}$

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

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

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:

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} + \text{Na}_2\text{CO}_3$

(b) Ethene from iodoethane:

$\underset{\text{ iodoethane}}{\text{C}_2\text{H}_5\text{I}} + \underset{\text{alcoholic}}{\text{KOH}} \xrightarrow{\text{boil}} \underset{\text{ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{KI} + \text{H}_2\text{O}$

(c) Ethyne from calcium carbide:

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \text{Ca(OH)}_2$

(d) Methanol from idomethane.

$\text{CH}_3\text{I} + \text{NaOH} \longrightarrow \text{CH}_3\text{OH} + \text{NaI}$

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

$\underset{\text{sodium propionate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} + \text{Na}_2\text{CO}_3$

(ii) Methane

$\underset{\text{methyl iodide}}{\text{CH}_3\text{I}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{methane}}{\text{CH}_4} +\text{HI}$

(iii) Ethene [ethylene]

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{alcoholic}}{\text{KOH}} \xrightarrow{\text{boil}} \underset{\text{ethene [ethylene]}}{\text{H}_2\text{C}=\text{C}\text{H}_2} + \text{KBr} + \text{H}_2\text{O}$

(iv) Methanol

$\text{CO} + 2\text{H}_2 \xrightarrow[\text{catalyst}]{\text{Zinc oxide}} \text{CH}_3\text{OH}$

(v) Ethyne [Acetylene]

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

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:

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \underset{\text{calcium hydroxide}}{\text{Ca(OH)}_2}$

(b) Ethene and water (steam).

$\underset{\text{ ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O} \xrightarrow[300\degree\text{C, 60 atm.}]{\text{H}_3\text{PO}_4} \underset{\text{ethene}}{\text{C}_2\text{H}_5\text{OH}}$

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

$\underset{\text{ Bromoethane [ethyl bromide]}}{\text{C}_2\text{H}_5\text{-Br}} + \underset{\text{ aqueous}}{\text{NaOH}} \xrightarrow{\text{boil}} \underset{ \text{ethanol}} {\text{C}_2\text{H}_5\text{OH}} + \text{NaBr}$

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 : C_nH_2n+1COOH (or RCOOH)

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

(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.

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.

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

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).

$\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}$

(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].

$\underset{\text{acetylene}}{\text{C}_2\text{H}_2} + \text{H}_2\text{O} \xrightarrow{\text{H}_2\text{SO}_4\text{(dil) , HgSO}_4}\underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}}$

The acetaldehyde is oxidised to acetic acid by passsing a mixture of acetaldehyde vapous and air over manganese acetate at 70°C

$\underset{\text{ethanal [acetaldehyde] }}{2\text{CH}_3\text{CHO}} + \text{O}_2 \xrightarrow[\text{Catalyst}]{\Delta} \underset{ \text{ethanoic acid[acetic acid]} }{2\text{CH}_3\text{COOH}}$

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.

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \text{CH}_3\text{COOH} \xrightarrow{\text{conc. H}_2\text{SO}_4} \underset{\text{ethyl acetate}}{{\text{CH}_3\text{COOC}_2\text{H}_5}} + \text{H}_2\text{O}$

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 ↑

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.

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)

(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.

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 —

$\underset{\text{cane sugar [molasses]}}{\text{C}_{12}\text{H}_{22}\text{O}_{11}} + \text{H}_2\text{O} \xrightarrow[\text{[yeast]}]{\text{invertase }} \underset{\text{glucose}}{{\text{C}_6\text{H}_{12}\text{O}_6}} + \underset{\text{fructose}}{{\text{C}_6\text{H}_{12}\text{O}_6}}$

$\underset{\text{glucose}}{{\text{C}_6\text{H}_{12}\text{O}_6}} \xrightarrow[\text{fermentation}]{\text{zymase [yeast]}} \underset{\text{ethanol}}{{2\text{C}_2\text{H}_{5}\text{OH}}} + 2\text{CO}_2$

Find the odd one out and explain:

C₃H₈, C₅H₁₀, C₂H₆, CH₄

Answer

C₅H₁₀

Reason — As it is not following the general alkane formula (C_nH_2n+2). It is an alkene with general formula C_nH_2n.

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 :

$\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3$

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

(c) ethyne from 1, 2 – dibromoethane.

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.

$\underset{\text{ Chloroethane [ethyl chloride]}}{\text{C}_2\text{H}_5\text{-Cl}} + \text{NaOH [aq.]} \xrightarrow{\text{boil}} \underset{\text{ Ethanol [ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} + \text{NaCl}$

(b) By boiling ethyl chloride with alcoholic KOH.

$\underset{\text{ Chloroethane [ethyl chloride]}}{\text{C}_2\text{H}_5\text{-Cl}} + \underset{\text{ alcoholic KOH}}{\text{KOH [aq.]}} \xrightarrow{\text{boil}} \underset{\text{ Ethene [ethylene]} }{\text{C}_2\text{H}_4} + \text{KCl} +\text{H}_2\text{O}$

(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.

$\underset{\text{ Ethene} }{\text{C}_2\text{H}_4} + \underset{\text{conc.}}{\text{H}_2\text{SO}_4} \underset{30 \text{ atmos.}}{\xrightarrow{80 \degree \text{C}}} \underset{\text{ Ethyl hydrogen sulphate} }{\text{C}_2\text{H}_5\text{-HSO}_4}$

$\underset{\text{ Ethyl hydrogen sulphate }}{\text{C}_2\text{H}_5\text{-HSO}_4} + \underset{\text{steam}}{\text{H}_2\text{O}} \longrightarrow \underset{ \text{ Ethanol [ethyl alcohol]} }{\text{C}_2\text{H}_5\text{-OH}} + \text{H}_2\text{SO}_4$

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

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

(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.

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:

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl ethanoate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}$

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

An organic weak acid is :

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

Answer

Formic acid

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

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

Answer

Methanol

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:

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

$\underset{\text{Ethene}}{\text{C}_2\text{H}_4} + \underset{\text{ water} }{\text{H}_2\text{O}} \underset{\text{acid}}{\xrightarrow{\text{H}}^+} \underset{\text{ ethanol} }{\text{C}_2\text{H}_5\text{OH}}$

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

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

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.

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.

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:

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 H₂SO₄, 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 H₂SO₄, 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.

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:

$\underset{\text{ Chloroethane [ethyl chloride]}}{\text{C}_2\text{H}_5\text{-Cl}} + \text{KOH [aq.]} \xrightarrow{\text{boil}} \underset{\text{ Ethanol [ethyl alcohol]} }{\text{C}_2\text{H}_5\text{-OH}} + \text{KCl}$

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

$\underset{\text{sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \underset{\Delta}{\xrightarrow{\text{CaO}}} \underset{\text{methane}}{\text{CH}_4} + \text{Na}_2\text{CO}_3$

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

$\underset{ \text{ ethanol[ethyl alcohol]}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{ethanal [acetaldehyde] }}{\text{CH}_3\text{CHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{ \text{ethanoic acid[acetic acid]} }{\text{CH}_3\text{COOH}}$

(iv) Water is added to calcium carbide:

$\underset{\text{calcium carbide}}{\text{CaC}_2} + \underset{\text{water}}{2\text{H}_2\text{O}} \longrightarrow \underset{\text{ethyne [acetylene]}}{\text{C}_2\text{H}_2} + \text{Ca(OH)}_2$

(v) Ethanol reacts with sodium at room temperature:

$\underset{\text{ ethanol} }{2\text{C}_2\text{H}_5\text{OH}} + 2\text{Na} \longrightarrow \underset{\text{ sodium ethoxide} }{2\text{C}_2\text{H}_5\text{ONa}} + \text{H}_2$

(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: