Hydrocarbon and its Compounds — Class 10 Science Guide [New Syllabus 2080/81]

                                              UNIT - 18                                               

1. Choose the best option for the following questions.

a. Which hydrocarbon is included in the alkane group?

i. Methane

ii. Ethene

iii. Acetylene

iv. Propyne

b. Which one is the correct formula of glycerol?

i. CH(OH)

ii. CH(OH)

iii. CH (OH),

iv. C₃H₅(OH)₃

c. Which of the following is the IUPAC name of the alcohol used as a beverage?

i. Methanol

ii. Ethanol

iii. Butanol

iv. Propanol

d. Which of the following is used to protect skin from dryness?

i. Methyl alcohol

ii. Ethyl alcohol

iii. Glycerol

iv. Glucose

e. Which hydrocarbon is used to prepare glycerol?

i. Methane

ii. Ethane

iii. Propane

iv. Glucose

2. Write differences between

a. Saturated and unsaturated hydrocarbon

Saturated Hydrocarbon	Unsaturated Hydrocarbon
1. The hydrocarbon having a single covalent bond between the carbon atoms is called saturated hydrocarbon.	1. The hydrocarbon having double or triple covalent bonds between the carbon atoms is called unsaturated hydrocarbon.
2. Saturated hydrocarbons are stable.	2. Unsaturated hydrocarbons are unstable.
3. They are also named as alkanes.	3. They are also named as alkenes or alkynes.
4. The general formula for saturated hydrocarbon is CnH2n+2, where n stands for number of carbon atoms.	4. The general formula for unsaturated hydrocarbon is CnH2n or CnH2n-2, where n stands for number of carbon atoms.
5. Example: Ethane, Propane etc.	5. Example: Ethyne, Propene etc.

b. Alkane and alkene

Alkane	Alkene
1. The hydrocarbon having a single covalent bond between the carbon atoms is called alkane.	1. The hydrocarbon having double covalent bonds between the carbon atoms is called alkene.
2. Alkane is saturated hydrocarbon and is stable.	2. Alkene is unsaturated hydrocarbon and is unstable.
3. The general formula for alkane is CnH2n+2	3. The general formula for alkene is CnH2n, where n stands for number of carbon atoms.
4. Example: Methane, Ethane etc.	4. Example: Ethene, Propene etc.

c. Monohydric alcohol and dihydric alcohol

Monohydric alcohol	Dihydric alcohol
1. The alcohol with only one hydroxyl (-OH) functional group bounded to a carbon atom is called Monohydric alcohol.	1. The alcohol which consists of two hydroxyl (-OH) functional group bounded to a carbon atom is called dihydric alcohol.
2. Example: Methanol (CH3OH)	2. Example: Glycol (CH2OH CH2OH)

3. Give reason

a. Ethane is known as a saturated hydrocarbon.

→ Ethane is known as a saturated hydrocarbon because the carbon atoms in ethane are connected only by a single bond.

b. Glycerol is called a trihydric alcohol

→ Glycerol is called a trihydric alcohol because it is a compound which contains three hydroxyl (-OH) functional groups bound to saturated carbon atoms.

4. Answer the following questions:

a. What are hydrocarbons? Write any four examples.

→ Those compounds which are formed by the combination of Carbon and Hydrogen atoms are called hydrocarbons.

Examples of hydrocarbons are Methane (CH₄), Ethene (C₂H₄), Propyne (C₃H₄), Methanol (CH₃OH) etc.

b. What do you mean by a saturated hydrocarbon? Write with examples.

→ Hydrocarbons in which carbon atoms are connected by a single bond is called saturated hydrocarbon.

Examples of saturated hydrocarbon are Methane, Ethane, Propane, Butane etc.

c. Introduce methane gas along with its two uses.

→ Methane is the simplest alkane (hydrocarbon) gas found in marshy place which is also called Marsh gas.  Its molecular formula is CH₄ and has dual nature of working as pollutant as well as commodity. Methane is colorless, odorless and tasteless gas. It’s insoluble in water but soluble in organic solvents.

Uses of Methane are as follows:

* It is used for cooking food as gobar gas or biogas and as fuel in industries.

* It can be used in industrial preparation of Hydrogen gas.

d. What is alcohol? Write its types on the basis of the hydroxyl group? Also write their examples along with their molecular formula and the structural formula.

→ The compound formed by the substitution of one or more hydrogen atoms of an alkane by hydroxyl group (-OH) is called alcohol.

— On the basis of hydroxyl group, alcohols are of three type’s viz. monohydric alcohol, dihydric alcohol and trihydric alcohol.

— One example of monohydric alcohol is Methanol. Its molecular formula is CH₃OH. Its structural formula is: 

— One example of dihydric alcohol is Ethanol. Its molecular formula is C₂ H₄(OH)₂. Its structural formula is:

— One example of trihydric alcohol is Glycerol. Its molecular formula is C₃ H ₅(OH)₃. Its structural formula is:

e. Write the molecular formula, condensed formula, and the structural formula of the following compounds.

Ethylene, propene, acetylene, ethyl alcohol, glycerol

→ Ethylene:

Molecular formula: C₂H₄

Condensed formula: CH₂=CH₂

Structural formula:

— Propene:

Molecular formula: C₃H₆

Condensed formula: CH₂=CHCH₃

Structural formula:

— Acetylene:

Molecular formula: C₂H₂

Condensed formula: CH≡CH

Structural formula:

— Ethyl alcohol:

Molecular formula: C₂H₅OH

Condensed formula: CH₃-CH₂OH

Structural formula:

— Glycerol

Molecular formula: C₃H₅(OH)₃

Condensed formula: CH₂OH – CHOH – CH₂OH

Structural formula:

f. Name the alcohol used for following purposes:

i. to make formaldehyde

ii. used in thermometer

iii. used as an antiseptic

iv. to prepare alcoholic beverages

→ To make formaldehyde: Methanol

– Used in thermometer: Ethanol

– Used as an antiseptic: Ethanol and Isopropyl alcohol

– To prepare alcoholic beverages: Ethanol

g. Write the structural formula of ethylene. What type of bond is found between its hydrogen and carbon? Why is the bond between its carbon atoms weak?

→ Structural formula of ethylene:

- All bond found in between carbon and hydrogen in ethylene are covalent suggesting that each bond are formed by sharing valence electrons.

h. Study the following structural formula of a hydrocarbon and answer the given questions. 

i. Write the name of this compound?

ii. Is it a saturated hydrocarbon? Write with reason.

iii. Which compound will form if one of the hydrogen atoms is replaced with a -OH group in the given compound?

 → The name of this compound is ethane.

- Yes, it is a saturated hydrocarbon because carbon atoms in it are connected by single bonds.

- Ethanol will be formed if one of the hydrogen atoms is replaced with a –OH group.

i. Write any three uses of methane gas.

→ The uses of methane gas are as follows:

- It can be used for cooking food as biogas or gobar gas and as fuel in industries.

- It is used to prepare lamp black which is used to make printing ink, shoe polish etc.

- It is also used to prepare chloroform.

j. Write major uses of each of ethane and propane.

→ Major uses of ethane are as follows:

- It is used in welding of metal as it produces heat on combustion.

- It is used to prepare carbonic compounds like ethyl chloride.

→ Major uses of propane are as follows:

- It is used as fuel as it is highly flammable.

- It is used in petroleum industries as a coolant.

- It is used to prepare different carbonic compounds.

k. Define the following terms.

i. Saturated hydrocarbon

ii. Unsaturated hydrocarbon

iii. Alkane

iv. Alkene

V. Alkyne

vi. Functional group

vii. Homologous series

→ Definitions:

i. Saturated hydrocarbon: Hydrocarbon in which carbon atoms are connected by a single covalent bond is called saturated hydrocarbon.

ii. Unsaturated hydrocarbon: Hydrocarbon in which carbon atoms are connected by double or triple covalent bond is called unsaturated hydrocarbon.

iii. Alkane: Hydrocarbon in which carbon atoms are connected by a single covalent bond is called alkane.

iv. Alkene: Hydrocarbon in which two carbon atoms are connected by a double covalent bond is called alkene.

V. Alkyne: Hydrocarbon in which two carbon atoms are connected by a triple covalent bond is called alkyne.

vi. Functional group: Atom or group of atoms on which chemical properties of compound depend is called functional group.

vii. Homologous series: The series of organic compounds having same functional groups and two successive members differs by CH₂ group are called Homologous series.

 

l. Write the molecular formula of the following compounds

Glycerol, methane, ethanol, butane, propane, acetylene, ethene, ethane, propyne, methyl alcohol

→ The molecular formula of these compounds are:

- Glycerol: C₃H₅(OH)₃

- Methane: CH₄

- Ethanol: C₂H₅OH

- Butane: C₄H₁₀

- Propane: C₃H₈

- Acetylene: C₂H₂ (Ethyne is also called Acetylene)

- Ethene: C₂H₄

- Ethane: C₂H₆

- Propyne: C₃H₄

- Methyl alcohol: CH₃OH

m. Write the name and structural formula of the alcohol used in spirit lamps.

→ Alcohol used in spirit lamps is ethyl alcohol (ethanol) which has molecular formula of C₂H₅OH.

Structural formula of ethanol is given as:

n. Name the compound formed by the replacement of three hydrogen atoms with three hydroxyl groups (-OH) from propane. Also write its IUPAC name along with its structural formula. Write its three uses.

→ When three hydrogen atoms are replaced by three hydroxyl groups (-OH) from propane, glycerol is formed.

- IUPAC name of glycerol is 1, 2, 3- Trihydroxypropane.

- Its structural formula is:

- The three major used of glycerol are as follows:

a. It is used to prevent skin from dryness by trapping moisture.

b. It is used as sweetening agent in foods.

c. It is used in cosmetics to make good quality soaps, lotions and creams.

o. Rama has a problem of dry skin in her hands, feet, and face. Which compound can be used to solve her problem? Write the IUPAC name and the structural formula of that compound.

→ Glycerol (Glycerine) can be used to solve Rama’s problem of dry skin because it allows the skin to retain its moisture as well as refreshes and soften the skin.

- IUPAC name of glycerol is propane 1,2,3 – triol or 1,2,3 – Trihydroxypropane.

 

REVIEW OF CHAPTER WITH SOME OTHER IMPORTANT QUESTIONS:

● Hydrocarbon: The compound which is formed by the bonding of carbon and hydrogen atom is called hydrocarbon.

● Naming of hydrocarbon: The IUPAC name of hydrocarbon is given with word root and suffix. The word root is determined by the number of carbon atoms. For example:

 

C₁  → Meth

C₂  → Eth

C₃  → Prop

C₄  → But

C₅  → Pent

C₆  → Hex

C₇  → Hept

C₈  → Oct

C₉  → Non

C₁₀ → Dec

C₁₁ → Hendec

C₁₂ → Dodec

 

The suffix is determined on the basis of bond between carbon atoms. It is determined as follows:

(i)             If all the carbon atoms are linked by single covalent bond then the suffix 'ane' is used.

(ii)         If two carbon atoms are linked by double covalent bond then the suffix 'ene' is used.

(iii)      If two carbon atoms are linked by triple covalent bond then the suffix 'yne' is used.

Examples:

(i)

(ii) 

IUPAC name: Ethene

(iii) 

IUPAC name: Ethyne

● Saturated hydrocarbons: The hydrocarbons in which carbon atoms are connected by a single covalent bond are called saturated hydrocarbons. For example: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈)etc. Saturated hydrocarbons are also called alkanes.

● Unsaturated hydrocarbons: The hydrocarbons in which carbon atoms are connected by double or triple covalent bonds are called Unsaturated Hydrocarbons. For example: Ethene (C₂H₄), Propene (C₃H₆), Butyne (C₄H₆) etc.

● Alkane: The hydrocarbon in which carbon atoms are connected by a single covalent bond is called alkane. For example: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈) etc.

● Alkene: The hydrocarbon in which two carbon atoms are connected by double covalent bond is called alkene. For example: Ethene (C₂H₄), Propene (C₃H₆) etc.

● Alkyne: The hydrocarbon in which two carbon atoms are connected by triple covalent bonds is called alkyne. For example: Ethyne ( C₂H₂ ),  Butyne (C₄H₆) etc.

● Isomers: The organic compounds which have same molecular formula but different structural formula are called isomers and the phenomenon is known as isomerism. Example: Butane has two isomers: They are n-butane (right) and iso-butane(left).

● Functional group: Atom or group of atoms on which chemical properties of compound depend is called functional group. Examples: Hydroxyl (-OH), Carboxylic acid (-COOH), Ether (-O-), aldehyde (-CHO) etc.

● Homologous series: The series of organic compounds having same functional groups and two successive members differs by CH₂ group are called homologous series. For example:

CH₃OH → Methanol

CH3-CH2-OH → Ethanol

CH-CH2-CH2-OH → Propanol

● Characteristics of homologous series:

- Homologous series have same functional group.

- They have same general formula.

- They have similar chemical properties.

- They can be prepared by using same general methods.

● Alcohols: The organic compounds which contain hydroxyl as functional group are called alcohols. For example: Methanol, Ethanol etc.  

● Monohydric alcohol: The alcohol having only one hydroxyl functional group (- OH) is called monohydric alcohol. For example: Methanol (CH₃ - OH), Ethanol (CH₃CH₂-OH) etc.

● Dihydric Alcohol: The alcohol having two hydroxyl functional groups (-OH) within a compound is called dihydric alcohol. For example: Ethyl glycol, Catechol etc

● Trihydric alcohol: The alcohol having three hydroxyl groups (-OH) in one compound is called trihydric alcohol. For example: Glycerol, propanetriol etc.

● Ether: The organic compound which has oxygen in between two alkyl groups is called ether. Eg: diethyl ether (C₄H₁₀O)

 

Some Important Question Answers:

1.   What are the sources of organic compounds?

→ The main sources of organic compounds are plants, animals, coal, petroleum oil etc.

 

2.   Why are alkanes called paraffines?

→ The alkanes are called paraffines because they are less reactive.

 

3.   State full form of IUPAC.

→  IUPAC stand for International Union of Pure and Applied Chemistry.

 

4.   What is cracking? Give example.

→ Cracking is the process of breaking of long chain hydrocarbons into light hydrocarbon by the action of heat. It is also called Pyrolysis.

Eg: C₆H₁₄→C₄H₁₀ + C₂H₄

 

5.   Give physical properties of ether.

→ Physical properties of ether are as follows:

a)   They are colorless and flammable substance.

b)  Ether which has 3 or less carbon atoms in them dissolve in water.

c)   They have lower boiling point compared to isomeric alcohol.

6.   Which alcohol is used to manufacture formaldehyde? [SLC 2069]

→ Methyl alcohol is used to manufacture formaldehyde.

 

7.   Study the following organic compound:  [SEE 2079] P₁

a)   Write molecular formula of the compound.

→ It’s molecular formula is C₂H₅OH

b)  In which group of organic compounds does this compound belong?

→ This compound belongs to alcohol/ hydroxyl (-OH) functional group.

 

8.    A saturated hydrocarbon is formed by the hydrogenation of alkene having 2 carbon atoms and general formula C_nH_2n. One of the reactants in the given reaction when burnt in air produces a gas which turns lime water milky. [SEE 2079] P₂

a)   Write the IUPAC names of reactant and product as described in the first statement.

→ The IUPAC name of reactant is ethene and product is ethane.

b)Write the balanced equation of reaction occurred in the first statement.

→ C₂H₄+ H₂ → C₂H₆

c)Write the name of milky compound formed as described in the second statement.

→ The name of milky compound thus formed is Calcium carbonate.

9.Write two differences between homologous series and functional group. [SEE 2079] P₄

→ The difference between homologous series and functional group are as follows: 

The series of organic compounds having same functional groups and two successive members differs by CH₂ group are called Homologous series. 

    Homologous series helps to arrange different chemical compound according to the similarity of chemical reactivity. 

    Homologous series have similar or nearly similar chemical reactivity among members of series. 

    Eg: Homologous series of alkane: methane, ethane, propane, butane etc. 

    Atom or group of atoms on which chemical properties of compound depend is called functional group. 

    Functional group helps in determining the chemical reactivity of a chemical compound. 

    Different functional group causes different chemical reactivity. 

    Eg: Functional group of alcohol is (-OH) hydroxyl group.

10.         Write the structural formula of following compounds:

a)   Trihydric alcohol having C₃H₈O₃

→ 

b)  Hydrocarbon with C₂H_2. [SEE 2079] P₇

→ 

11. An organic compound has elements C, H and O in it. It is used in thermometers.

a)Identify it and write its functional group.

→ The organic compound used in thermometer having C,H,O is ethyl alcohol. Its functional group is –OH.

b)Write IUPAC name of it.

→ Its IUPAC name is ethanol.

c)Write the name of traditional method of preparation of this compound. [SEE 2079] P₅

→ Fermentation technique is used to prepare ethanol traditionally.

12. Structural formula of some compounds are given below:

(A)

(B) 

(C) 

a)Which one of them is unsaturated hydrocarbon?

→  (B) is unsaturated hydrocarbon and its name is ethene.

b)  Write any one use of ‘C’. [SEE 2079] P₃

→ Compound in ( C ) is glycerol which can be used to prevent skin from cracks and make it moist & smooth.

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