Hydrocarbon and its Compounds

1. Summary: Hydrocarbon and its Compounds

2.1 Choose the best option for the following questions:

2.2 Write differences between:

(a) Saturated and Unsaturated Hydrocarbon

S.N.	Saturated Hydrocarbon	Unsaturated Hydrocarbon
1.	They contain only single covalent bonds (C-C) between carbon atoms.	They contain at least one double (C=C) or triple ($C\equiv C$) bond between carbon atoms.
2.	They are generally less reactive (also called paraffins).	They are chemically more reactive due to the presence of multiple bonds.
3.	They burn with a clear, non-sooty blue flame (complete combustion).	They often burn with a yellow, sooty flame (incomplete combustion).
4.	They undergo substitution reactions (hydrogen is replaced by other atoms).	They undergo addition reactions (atoms are added to the multiple bond).
5.	Example: Methane ($CH_4$), Ethane ($C_2H_6$).	Example: Ethene ($C_2H_4$), Acetylene ($C_2H_2$).

(b) Alkane and Alkene

S.N.	Alkane	Alkene
1.	Hydrocarbons with single bonds between carbon atoms.	Hydrocarbons with at least one double bond between carbon atoms.
2.	Their general formula is $C_nH_{2n+2}$.	Their general formula is $C_nH_{2n}$.
3.	They are saturated hydrocarbons.	They are unsaturated hydrocarbons.
4.	They are relatively stable and less reactive.	They are unstable and highly reactive compared to alkanes.
5.	Example: Propane ($C_3H_8$).	Example: Propene ($C_3H_6$).

(c) Monohydric alcohol and Dihydric alcohol

S.N.	Monohydric Alcohol	Dihydric Alcohol
1.	Alcohols containing only one hydroxyl (-OH) group.	Alcohols containing two hydroxyl (-OH) groups.
2.	Derived by replacing one hydrogen of an alkane with -OH.	Derived by replacing two hydrogens of a hydrocarbon with -OH groups.
3.	General formula: $C_nH_{2n+1}OH$.	General formula: $C_nH_{2n}(OH)_2$ (Glycols).
4.	Generally have lower boiling points compared to dihydric alcohols of similar mass.	Have higher boiling points due to stronger hydrogen bonding (two -OH groups).
5.	Example: Methanol ($CH_3OH$), Ethanol ($C_2H_5OH$).	Example: Ethylene glycol ($C_2H_4(OH)_2$).

2.3 Give reason:

(a) Ethane is known as a saturated hydrocarbon.

Reason: Ethane ($C_2H_6$) is called a saturated hydrocarbon because all the four valencies of its carbon atoms are fully satisfied by single covalent bonds. It does not contain any double or triple bonds between carbon atoms, meaning it cannot add any more atoms to its structure without replacing existing ones (substitution).

(b) Glycerol is called a trihydric alcohol.

Reason: Glycerol ($C_3H_5(OH)_3$) is called a trihydric alcohol because its molecule contains three hydroxyl groups (-OH) attached to three different carbon atoms in its hydrocarbon chain. The term “trihydric” specifically refers to the presence of three -OH groups.

2.4 Answer the following questions:

(a) What are hydrocarbons? Write any four examples.

Answer: Hydrocarbons are organic compounds composed essentially of carbon and hydrogen atoms only.

Examples:

• Methane ($CH_4$)

• Ethane ($C_2H_6$)

• Ethene ($C_2H_4$)

• Acetylene ($C_2H_2$)

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

Answer: A saturated hydrocarbon is a hydrocarbon in which carbon atoms are connected to each other only by single covalent bonds. They are chemically less reactive.

Examples: Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$).

(c) Introduce methane gas along with its two uses.

Answer: Methane is the simplest saturated hydrocarbon (alkane) with the molecular formula $CH_4$. It is the primary component of natural gas and bio-gas (Gobar gas). It is found in marshy areas and coal mines.

Uses:

• It is used as a domestic and industrial fuel (in the form of LPG, CNG, or bio-gas) because it produces a lot of heat upon burning.

• It is used in the manufacture of industrial chemicals like methyl alcohol, formaldehyde, and chloroform.

(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.

Answer: Alcohol is an organic compound formed by replacing one or more hydrogen atoms of a hydrocarbon with hydroxyl groups (-OH).

Types based on hydroxyl group:

1. Monohydric Alcohol: Contains 1 -OH group.

• Example: Methanol ($CH_3OH$)

• Structure: $CH_3-OH$

2. Dihydric Alcohol: Contains 2 -OH groups.

• Example: Ethylene glycol ($C_2H_6O_2$)

• Structure: $CH_2OH-CH_2OH$

3. Trihydric Alcohol: Contains 3 -OH groups.

• Example: Glycerol ($C_3H_8O_3$)

• Structure: $CH_2OH-CHOH-CH_2OH$

(e) Write the molecular formula, condensed formula, and the structural formula of the following compounds:

Compound	Molecular Formula	Condensed Formula	Structural Formula
Ethylene	$C_2H_4$	$CH_2=CH_2$	H₂C=CH₂
Propene	$C_3H_6$	$CH_3CH=CH_2$	CH₃-CH=CH₂
Acetylene	$C_2H_2$	$CH\equiv CH$	H-C≡C-H
Ethyl alcohol	$C_2H_6O$	$C_2H_5OH$	CH₃-CH₂-OH
Glycerol	$C_3H_8O_3$	$C_3H_5(OH)_3$	CH₂OH-CHOH-CH₂OH

(f) Name the alcohol used for the following purposes:

i. To make formaldehyde: Methanol (Methyl Alcohol)

ii. Used in thermometers: Ethanol (Ethyl Alcohol) (due to its low freezing point of -114°C)

iii. Used as an antiseptic: Ethanol (Ethyl Alcohol)

iv. To prepare alcoholic beverages: Ethanol (Ethyl Alcohol)

(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:

Bond between Hydrogen and Carbon: Single covalent bond (Sigma bond).

Why C=C is weak: The double bond between carbon atoms consists of one strong Sigma ($\sigma$) bond and one weak Pi ($\pi$) bond. The Pi bond is formed by the sideways overlap of orbitals, making it weaker and easily broken during reactions, which makes ethylene reactive.

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

i. Write the name of this compound: The compound is Ethane.

ii. Is it a saturated hydrocarbon? Write with reason. Yes, it is a saturated hydrocarbon because it contains only a single bond (C-C) between the two carbon atoms.

iii. Which compound will form if one of the hydrogen atoms is replaced with a -OH group in the given compound? If one H is replaced by -OH, Ethyl Alcohol (Ethanol) is formed. ($C_2H_5OH$).

(i) Write any three uses of methane gas.

Answer:

• Used as a fuel for cooking and heating (Natural Gas/Bio-gas)

• Used to manufacture hydrogen gas and carbon black

• Used as a raw material for making fertilizers (via hydrogen production)

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

Answer:

Ethane: Used as a fuel and used to produce ethene (ethylene) which is essential for making plastics.

Propane: Primarily used as a fuel (LPG – Liquefied Petroleum Gas) for heating, cooking, and vehicles. It is also used as a refrigerant.

(k) Define the following terms:

i. Saturated hydrocarbon: Hydrocarbons containing only single covalent bonds between carbon atoms.

ii. Unsaturated hydrocarbon: Hydrocarbons containing at least one double or triple bond between carbon atoms.

iii. Alkane: A homologous series of saturated hydrocarbons with the general formula $C_nH_{2n+2}$.

iv. Alkene: An unsaturated hydrocarbon containing a carbon-carbon double bond, with general formula $C_nH_{2n}$.

v. Alkyne: An unsaturated hydrocarbon containing a carbon-carbon triple bond, with general formula $C_nH_{2n-2}$.

vi. Functional group: An atom or group of atoms present in a molecule that determines the specific chemical properties of that organic compound (e.g., -OH for alcohols).

vii. Homologous series: A family of organic compounds having the same functional group, similar chemical properties, and successive members differing by a $-CH_2-$ group.

(l) Write the molecular formula of the following compounds:

• Glycerol: $C_3H_5(OH)_3$

• Methane: $CH_4$

• Ethanol: $C_2H_5OH$

• Butane: $C_4H_{10}$

• Propane: $C_3H_8$

• Acetylene: $C_2H_2$

• Ethene: $C_2H_4$

• Ethane: $C_2H_6$

• Propyne: $C_3H_4$

• Methyl alcohol: $CH_3OH$

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

Name: Methyl Alcohol (Methanol) or Methylated Spirit (Ethanol mixed with Methanol). In the context of the book emphasizing specific alcohols, Methyl Alcohol is often cited for industrial/fuel use, but Ethanol is also common. The most specific answer is Methyl Alcohol.

Structural Formula (Methanol):

(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.

Name: Glycerol (Common name)

IUPAC Name: Propane-1,2,3-triol

Structural Formula:

Three Uses:

• Used to make high-quality soaps and cosmetics

• Used as a moisturizing agent for skin (treats dryness)

• Used as a sweetening agent in beverages and confectionery

(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.

Compound: Glycerol (often mixed with rose water and lemon juice for skin application)

IUPAC Name: Propane-1,2,3-triol

Structural Formula: