Question

What are hydrocarbons ?

Answer 1

Step 1: Understanding the term "hydrocarbons":
The word "hydrocarbon" is made up of two parts: "hydro" refers to hydrogen and "carbon" refers to carbon atoms.

Step 2: Composition of hydrocarbons:
Hydrocarbons are organic compounds that consist of only two elements:
- Carbon (C)
- Hydrogen (H)
These elements combine in various ways to form a wide range of compounds.

Step 3: Types of hydrocarbons:
Hydrocarbons are mainly classified into:
- Alkanes: Saturated hydrocarbons with single bonds (e.g., methane CH₄)
- Alkenes: Unsaturated hydrocarbons with one or more double bonds (e.g., ethene C₂H₄)
- Alkynes: Unsaturated hydrocarbons with one or more triple bonds (e.g., ethyne C₂H₂)
- Aromatic hydrocarbons: Compounds that contain a benzene ring (e.g., benzene C₆H₆)

Step 4: Conclusion:

Hydrocarbons are organic compounds composed of only two elements: carbon and hydrogen.

Answer 2

Step 1: Understanding why carbon forms many compounds:
Carbon is a unique element in the periodic table that can form millions of compounds. This is due to two special properties it possesses.

Step 2: Property 1 – Tetravalency:
- Carbon has an atomic number of 6, and its electronic configuration is 2, 4.
- It has 4 valence electrons and needs 4 more to complete its octet.
- Therefore, carbon forms four covalent bonds with other atoms like hydrogen, oxygen, nitrogen, or even other carbon atoms.
- This tetravalency allows carbon to form a wide variety of stable molecules with different elements.

Step 3: Property 2 – Catenation:
- Carbon atoms can bond with other carbon atoms to form long chains, branched chains, or rings.
- This property is called catenation.
- The carbon-carbon bonds are strong and stable, which makes it possible to create very large and complex molecules such as hydrocarbons, proteins, and DNA.

Step 4: Conclusion:
Two properties that enable carbon to form a large number of compounds are:
1. Tetravalency: Ability to form four covalent bonds.
2. Catenation: Ability to form strong covalent bonds with other carbon atoms, forming long chains and complex structures.

Answer 3

Step 1: Functional groups in aldehydes and ketones:
1. Aldehydes: The functional group present in aldehydes is the aldehyde group (-CHO).
    Example: Formaldehyde (H–CHO), Acetaldehyde (CH₃–CHO)

2. Ketones: The functional group present in ketones is the ketone group (>C=O), also written as (-CO-).
    Example: Propanone (CH₃–CO–CH₃)

Step 2: Reaction between ethanoic acid and ethanol:
- Ethanoic acid: CH₃COOH
- Ethanol: C₂H₅OH
- Catalyst: Concentrated H₂SO₄ (sulfuric acid)
- This is an esterification reaction.

Step 3: Chemical equation:
CH₃COOH + C₂H₅OH  $\xrightarrow{\text{conc. H}_2\text{SO}_4}$  CH₃COOC₂H₅ + H₂O
(Ethanoic acid + Ethanol → Ethyl ethanoate + Water)

Step 4: Conclusion:
- The functional group in aldehydes is –CHO.
- The functional group in ketones is >C=O.
- Ethanoic acid reacts with ethanol in the presence of concentrated sulfuric acid to form an ester (ethyl ethanoate) and water. This is an example of an esterification reaction.

Answer 4

Step 1: Define structural isomers:
Structural isomers are compounds that have the same molecular formula but different structural formulas. This means they contain the same number and types of atoms, but the atoms are arranged in a different way within the molecule.

Step 2: Molecular formula of Butane:
The molecular formula of butane is C₄H₁₀.
It has two structural isomers because the carbon atoms can be arranged in two different ways while still maintaining the same molecular formula.

Step 3: Structure of the first isomer – n-Butane:
In n-butane, the carbon atoms are arranged in a straight chain:
CH₃–CH₂–CH₂–CH₃
This is a linear structure with no branching.

Step 4: Structure of the second isomer – Isobutane (Methylpropane):
In isobutane, the carbon atoms are arranged with a branching at the second carbon:
CH₃–CH(CH₃)–CH₃
Alternatively, it can be represented as a branched structure (as shown in the image).

Step 5: Conclusion:
The two structural isomers of butane (C₄H₁₀) are:
1. n-Butane: CH₃–CH₂–CH₂–CH₃
2. Isobutane (Methylpropane): CH₃–CH(CH₃)–CH₃
These are structural isomers because they have the same molecular formula but different structures.