CARBON AND ITS COMPOUNDS (B)Hydrocarbons-10th Science Notes and Question Bank

CHAPTER-12

CARBON AND ITS COMPOUNDS

(B)Hydrocarbons

Text Book Question and Answers

I. Answer the following

1. Classify the following into saturated and unsaturated hydrocarbons.

Benxene, cyclopropane, alkene, alkane,

Saturated hydrocarbons: Cycloproparne, Alkane

Unsaturated hydrocarbons: Benxene, alkene

2. Classify the compounds containing double bond and triple bond, ethyne, benzene, butyne, pentene.

Double bond: Benzene, Pentene

Triple bond: Ethyne, Butyne

II. Give reasons for the following

1. Alkanes as chemically stable.

Alkanes are chemically stable as they have only single bonds.

2. Alkanes undergo only substitution reactions but alkenes and alkynes undrgo both substitution and addition reactions. Why?

Alkanes undergo only substitution reactions as they are saturated whereas alkenes and alkynes undergo both substitution and addition reaction as they are unsaturated with double and triple bonds.

III. Answer the following

1. What is homologous series? Give an example of such series.

A homologous series is a family of organic compounds with the same general formula, similar chemical properties and successive members differing by –CH₂

Eg: Alkanes, Alkenes and Alkynes are homologous series of aliphatic hydrocarbons.

2. Define isomerism. Give examples

The compounds having same molecular formula but different structural formula are called isomers and the phenomenon is called isomerism

Eg:-Butane (C₄H₁₀)

3. Write the functional group present in methanal. Methanol. Methanoic acid and in amino acid.

Compound	Functional Group
Methanal	-CHO
Methanol	-OH
Methanoic acid	-COOH
Amino acid	NH₂-COOH

4. Write the structures of following

i. Isobutane C₄H₁₀

ii. Benzene C₆H₆

iii. Cyclohexane C₆H₁₂

iv. Ethane C₂H₄

v. Propyne C₃H₄

vi. Methanol CH₃OH

5. Mention the uses of benzene.

a) As a solvent for oils, fats, resins, rubber, sulphur, iodine etc.

b) In the manufacture of dyes, drugs, perfumes, explosives etc.

c) In the preparation of gammexane, an insecticide,

d) For dry cleaning.

6. What ldoes IUPAC represent?

International Union of Pure and Applied Chemistry

7. Draw the formulae of the first four members of each homologous series beginning with the following compounds.

IV. Choose the correct answer from the four alternatives given below

1. When three hydrogen atoms of methane molecule are substituted by three chlorine atoms. We get

(a)DDT (b)Chloroform (c)Methyl alcohol (d) CFC (chloroflurocarbons)

Answer:(b) Chloroform

2. The molecular formula of an alkane containing five carbon atoms is

(a)C₅H₈ (b)C₅H₁₀ (c)C₅H₅ (d)C₅H₁₂

Answer:(d) C₅H₁₂

3. The following hydrocarbons contain three double bonds.

(a)ethane (b)ethene (c)benzene (d)cyclohexane

Answer:(c) Benzene

4. The number of hydrogen atoms to be added to benzene to make it cyclohexane is

(a)two (b)three (c)four (d)six

Answer:(d) Six

5. In ethane, each carbon is bonded to

(a)six atoms (b)Three atoms (c)two atoms (d)four atoms

Answer:(d) Four atoms

6. General formula for an alkyne is

(a) C_nH_2n (b)C_nH_4n (c)C_nH_2n-2(d)CnH_2n+1

Answer:(c) C_nH_2n-2

V. Match the following

1. Aromatic hydrocarbons - Toluene

2. Alicyclic hydrocarbons - Cyclopropane

3. Alkenes - Ethene

4. Polyfuctional compound – Amino acid

Additional Question and Answers

1. What are hydrocarbons? Give examples

Hydrocarbons are the simplest binary organic compounds containing carbon and hydrogen only.

Eg:-Methane and Propane (gases), Hexane and benzene (liquids), Paraffin and Naphthalene (waxes or low melting solids) etc.

2. Which is the simplest hydrocarbon? Write its molecular formula.

The simplest hydrocarbon is called methane, its molecular formula is CH₄.

3. Give four examples of hydrocarbons commonly used in our day-to-day life.

Commonly used hydrocarbons in our day-to-day life include camphor, naphthalene, LPG, kerosene, petrol, cooking oils etc.

4. List the general properties of hydrocarbons.

Hydrocarbons are compounds which contain only carbon and hydrogen atoms. Some of the hydrocarbons are solids, a few are liquids and the rest are gases at room temperature. They have low melting and boiling points. Many of the hydrocarbons combine with their own molecules m large numbers to form polymers. Hydrocarbons may have a single bond, a double bond or a triple bond between their carbon atoms.

5. Name the two principal sources of hydrocarbons.

Petroleum and Coal

6. Where do you obtain aliphatic and aromatic hydrocarbons?

Aliphatic hydrocarbons are mainly obtained by petroleum

Aromatic hydrocarbons are mainly obtained from coal.

7. Mention the nature of hydrocarbons.

Hydrocarbons can be gases (e.g. Methane and propane), can be liquids (e.g. Hexane and pentane), Waxes or low melting solids (e.g. paraffin wax and naphthalene). Polymers (e.g. polyethylene and polypropylene)

8. Write the two classification of hydrocarbon

Based on structure, hydrocarbons are classified into two main groups

1. Open chain or acyclic compounds.

2. Closed chain or cyclic (or ring) compound.

Classifications of hydrocarbons

9. List five hydrocarbons used in our daily life and classify them into solids, liquids and gases bused on their physical state at room temperature.

Hydrocarbons that we use in our daily life include kerosene, petrol, methane, butane, candle wax, polythene, etc.

Hydrocarbons that are solids at room temperature: Candle wax and polythene

Hydrocarbons that are liquids at room temperature. Kerosene and petrol

Hydrocarbons that are gases at room temperature: Methane and butane.

10. What are aliphatic hydrocarbons?

Aliphatic hydrocarbons are also called acyclic or open chain hydrocarbons. These hydrocarbons consist of straight or branched chains of carbon atoms.

11. Differentiate between Aliphatic and cyclic hydrocarbons.

Aliphatic hydrocarbons	Cyclic hydrocarbons
Open chain	Closed chain
No aromatic ring	These are having at least one aromatic ring

12. Write the general formula of alkanes, alkenes and alkynes.

Alkanes C_nH_2n+2

Alkenes C_nH_2n

Alkynes C_nH_2n-2

13. Differentiate between saturated and unsaturated hydrocarbons.

Saturated	Unsaturated
They have single bond between carbon atoms	They have double or triple bond between carbon atoms
The general formula is C_nH_2n+2	The general formula is C_nH_2nor C_nH_2n-2
They are less reactive when compare to unsaturated hydrocarbons	They are more reactive when compared to saturated hydrocarbons
Eg:-Alkanes	Eg;-Alkenes and Alkynes

14. What are the general properties of acyclic hydrocarbons?

Acyclic hydrocarbons have open chain structure. The chains may be of either straight or branched structure. The molecules of these compounds may have a single, double or triple bond between their carbons

15. What are Alkanes? Give example with their structural formula

These are saturated hydrocarbons having single bond between carbon atoms. Their general formula is C_nH_2n+2(n= Number of carbon atoms)

16. Why are alkanes called paraffins?

Alkanes are saturated hydrocarbons. They have very little affinity for chemical reactions. Hence they are called paraffins. These are hence saturated hydrocarbons

17. What are Alkenes? Give example with structural formula

Alkenes are unsaturated hydrocarbons having double bond between two carbon atoms, their general formula is C_nH_2n (n= Number of carbon atoms)

18. What are alkynes? Give examples with their structure.

Alkynes are unsaturated hydrocarbons having triple bond between two carbon atoms, their general formula is C_nH_2n-2(n= Number of carbon atoms)

19. Write the indication of prefix in hydrocarbons.

Prefix or word root	Number of carbon atoms
Meth-	1
Eth-	2
Prop-	3
But-	4
Pent-	5
Hex-	6
Hept-	7
Oct-	8
Non-	9
Dec-	10

20. Write the indication of Primary suffixes in hydrocarbons.

21. Why Methane is called marsh gas?

It is because Methane is formed in the marshy places by the bacterial decomposition of organic matter

22. Explain the preparation of Methane (CH₄) in laboratory?

A mixture of sodium acetate and soda lime (NaOH+Cao) is heated in hard glass test tube and methane gas is evolved. It is collected by the downward.

CH₃COONa + NaOH -------Cao------- > Na₂CO₃ + CH₄

23. Methane gas is collected by downward displacement of water why?

Because methane gas is lighter than air and it is slightly soluble in water

24. Why is methane chemically inert?

Methane is a saturated hydrocarbon. This is why methane is chemically inert. However, it gives substitution reactions wherein the hydrogen atoms are replaced by atoms of other elements.

25. Write the properties of Methane?

Physical properties: - Methane is colourless, odourless gas, lighter than air. It is slightly soluble in water and fairly soluble in organic solvents

Chemical properties: - Methane is chemically inert. It will not react with by acids, alkalies and oxidizing agents

26. Explain the combustibility of methane?

Complete combustion (blue flame):-

CH₄ (g) + 2O₂(g) ------ > CO₂(g) +2H₂O(l)

Incomplete combustion (golden yellow flame) :-

2CH₄(g)+3O₂(g) -------> 2CO(g)+4H₂O(l)

27. Why carbon monoxide is poisonous?

Carbon monoxide acts as a poison by combining with haemoglobin in blood forming carboxy haemoglobin, which prevents the transportation of oxygen to the tissues and finally leads to death of a person by suffocation

28. What is substitution reaction?

Chemical reaction in which an atom or ion in a molecule is replaced by another atom or ion

29. Explain the substitution reaction which occurs in methane

When a mixture of methane and chlorine is exposed to ultraviolet light – typically sunlight – a substitution reaction occurs and the organic product chloromethane is formed.

CH₄ + Cl₂ ----uv--- > CH₃Cl + HCl

However, the reaction doesn’t stop there, and all the hydrogen’s in the methane can in turn be replaced by chlorine atoms to produce substitution products like chloromethane, dichloromethane, trichloromethane(chloroform) and tetrachloromethane (carbon tetrachloride)

CH₄ + Cl₂----uv--- > CH₃Cl + HCl

CH₃Cl + Cl₂----uv--- > CH₂Cl₂ + HCl

CH₂Cl₂ + Cl₂ ----uv--- > CHCl₃ + HCl

CHCl₃ + Cl₂ ----uv--- > CCl₄ + HCl

30. Define Homologous Series

A homologous series is a family of organic compounds with the same general formula, similar chemical properties, and successive members differing by –CH₂

31. List out the important characteristics of members of a homologous series.

a) They have properties that vary in a regular and predictable manner.

b) They have similar chemical properties

c) They have gradually varying physical properties

d) Their formulae fit the general molecular formula

e) Adjacent members CH₄ and C₂H₆ or C₅H₁₂ and C₆H₁₄ differ by one carbon and two hydrogen’s.

32. What are cycloalkanes? Give examples.

Cycloalkanes are closed chain saturated hydrocarbon having general formula C_nH_2n