Hydrocarbons

The functional group R–COO–R' represents an ester. Esters are prepared by the reaction between a carboxylic acid (RCOOH) and an alcohol (R'OH). This reaction is known as esterification: So, the correct reactants for forming an ester are RCOOH and R'OH.

The correct answer is option (A): RCOOH and R'OH

Correct answer: amides

Explanation:
Hydrocarbons that contain the —CONH₂ functional group are called amides. This group consists of a carbonyl group (C=O) bonded to a nitrogen atom (NH₂).

Here’s a comparison with other groups for clarity:
• Carboxylic acids: Contain —COOH group
• Amines: Contain —NH₂, —NHR or —NR₂ groups (no carbonyl)
• Esters: Contain —COOR group

Therefore, the correct classification for compounds with —CONH₂ is amides.

Correct answer: All of these

Explanation:
In hydrocarbons, carbon atoms exhibit tetravalency, meaning each carbon atom forms four covalent bonds. These can be arranged in different ways, giving rise to different types of hydrocarbons:

• Alkanes: Carbon forms four single bonds (e.g., CH₄ - methane).
• Alkenes: Carbon forms one double bond and two single bonds (e.g., C₂H₄ - ethene).
• Alkynes: Carbon forms one triple bond and one single bond (e.g., C₂H₂ - ethyne).

Hence, carbon can form all of these types of bonds in different hydrocarbons.

Correct answer: increases

Explanation:
In hydrocarbons, as the molecular formula increases (i.e., as the number of carbon atoms increases), the size and mass of the molecule also increase. This leads to stronger van der Waals forces (intermolecular forces) between the molecules.

Stronger intermolecular forces require more energy (in the form of heat) to overcome, which results in a higher melting point.

Thus, for hydrocarbons, when the molecular formula increases, the melting point increases.

Correct answer: alkanes

Explanation:
Hydrocarbons are organic compounds made up of carbon and hydrogen. Based on the types of bonds between carbon atoms, they are classified as:

- Alkanes: Contain only single bonds between carbon atoms. They are also called saturated hydrocarbons. Example: methane (CH₄), ethane (C₂H₆)
- Alkenes: Contain at least one double bond between carbon atoms. Example: ethene (C₂H₄)
- Alkynes: Contain at least one triple bond between carbon atoms. Example: ethyne (C₂H₂)

Therefore, hydrocarbons with only single bonds are called alkanes.

Ethene and ethyne are both hydrocarbons containing two carbon atoms.

Ethene ( ) has a double bond between the two carbon atoms and four hydrogen atoms. Its structure is .
Ethyne ( ) has a triple bond between the two carbon atoms and two hydrogen atoms. Its structure is .

Comparing ethene and ethyne:

Number of carbons: Both have 2 carbon atoms, so they don't differ in the number of carbons. *
Number of bonds: Ethene has a double bond, while ethyne has a triple bond. Therefore, they differ in the number of bonds. *
Number of hydrogens: Ethene has 4 hydrogen atoms, while ethyne has 2 hydrogen atoms.

Therefore, they differ in the number of hydrogens. Since ethene and ethyne differ in the number of bonds and the number of hydrogens, the correct answer is (4).

Saturated hydrocarbons, also known as alkanes, consist only of single bonds between carbon atoms, with each carbon atom bonded to as many hydrogen atoms as possible.

Aliphatic hydrocarbons are hydrocarbons that do not contain any aromatic rings. They can be either straight-chain, branched-chain (acyclic/open chain), or cyclic alkanes (alicyclic hydrocarbons).

(1) Closed chain hydrocarbons: These are cyclic hydrocarbons.
(2) Acyclic hydrocarbons: These are non-cyclic hydrocarbons.
(3) Open chain hydrocarbons: These are the same as acyclic hydrocarbons.

Since aliphatic hydrocarbons can be acyclic or open-chain hydrocarbons, the correct answer is (4).