Saturated and Unsaturated Hydrocarbons – Long Answer Questions

Medium Level (Application & Explanation)

Answer:

Saturated hydrocarbons have only single bonds between carbon atoms.
Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms.
Examples of saturated hydrocarbons:
1. Methane (CH₄) – All C–H single bonds; used as domestic fuel.
2. Ethane (C₂H₆) – All single C–C and C–H bonds; found in natural gas.
Examples of unsaturated hydrocarbons:
1. Ethene (C₂H₄) – Contains a double bond; used in ripening fruits.
2. Ethyne (C₂H₂) – Contains a triple bond; used in welding.

Answer:

Alkanes have only single covalent bonds between all carbon atoms.
Because of these single bonds, every carbon atom is bonded to as many hydrogen atoms as possible.
This is why alkanes are called "saturated" – all possible hydrogen sites are filled.
Example:
Ethane (C₂H₆):
     H    H
      |     |
H–C–C–H
      |     |
     H    H
There are no double or triple bonds in this structure.
As a result, no more hydrogen atoms can be added.

Answer:

Alkenes and alkynes have at least one double or triple bond between carbon atoms.
Because of these multiple bonds, they do not have the maximum number of hydrogen atoms, making them "unsaturated".
For example:
- Ethene (C₂H₄) has a double bond (C=C), so fewer hydrogens are attached.
- Ethyne (C₂H₂) has a triple bond (C≡C), also resulting in fewer hydrogens.
These double or triple bonds can be broken to add more hydrogens.
Thus, new atoms can add to these molecules, indicating they are unsaturated.

Answer:

Saturated hydrocarbons (alkanes) are mostly unreactive except under special conditions.
They usually undergo substitution reactions, where an atom (like hydrogen) is replaced by another (like chlorine).
For example:
- When methane reacts with chlorine in the presence of sunlight:
  CH₄ + Cl₂ → CH₃Cl + HCl
Unsaturated hydrocarbons are more reactive due to the presence of double or triple bonds.
They undergo addition reactions where atoms can add to the molecule.
Example: Ethene reacts with hydrogen in the presence of nickel catalyst:
C₂H₄ + H₂ → C₂H₆
The extra bonds in unsaturated hydrocarbons make them more chemically active.

Answer:

Alkanes: General formula is CₙH₂ₙ₊₂.
Alkenes: General formula is CₙH₂ₙ.
Alkynes: General formula is CₙH₂ₙ₋₂.
This means:
- Alkanes have the maximum number of hydrogen atoms per carbon, indicating single bonds only.
- Alkenes have less hydrogen, so at least one double bond is present.
- Alkynes have even fewer hydrogens, which means at least one triple bond.
The decrease in hydrogen counts shows the increase in multiple bonds.
The more the double or triple bonds, the less "hydrogen-saturated" the molecule is.

Answer:

The molecular formula for alkanes is CₙH₂ₙ₊₂. For n=4 (butane), it should be C₄H₁₀.
Here, the given hydrocarbon is C₄H₈, which matches the formula for alkenes (CₙH₂ₙ) and cycloalkanes.
This means C₄H₈ is unsaturated if it has a double bond (as in butene), or it could be a cyclic alkane.
If it's an open-chain molecule with a double bond, it's an alkene.
Since unsaturated compounds have less hydrogen, C₄H₈ must have at least one double bond or be cyclic.
Therefore, C₄H₈ is an unsaturated hydrocarbon.

Answer:

Saturated hydrocarbons (alkanes) are commonly used as fuels.
1. Methane (CH₄): Domestic cooking gas.
2. Propane (C₃H₈): In LPG cylinders for cooking and heating.
Unsaturated hydrocarbons are widely used in industry and agriculture.
1. Ethene (C₂H₄): Used to ripen fruits and in plastic production.
2. Ethyne (C₂H₂): Used in oxy-acetylene welding for cutting and joining metals.
Thus, both types play important roles in daily life but have different applications due to their chemical properties.

Answer:

Bromine water test is used to detect unsaturation in hydrocarbons.
If the reddish color disappears, the hydrocarbon is unsaturated (contains double or triple bonds).
The double or triple bond reacts with bromine, decolorizing the solution.
If the color does not change, the sample is saturated (has only single bonds) and does not react with bromine.
Therefore, the sample where bromine is decolorized is an alkene or alkyne, while the one with no color change is an alkane.
This test helps differentiate saturated and unsaturated substances.

Answer:

Both saturated and unsaturated hydrocarbons produce carbon dioxide and water when burned completely, but they differ in their tendency to burn cleanly.
Saturated hydrocarbons burn with a clean blue flame and produce less soot.
Unsaturated hydrocarbons often burn with a yellow, sooty flame due to incomplete combustion and higher carbon content.
Excess soot is harmful to the environment and can cause air pollution.
Therefore, saturated hydrocarbons (like LPG and CNG) are generally preferred as fuels for domestic and industrial purposes.
They are cleaner, safer, and less polluting compared to unsaturated hydrocarbons.

Answer:

The structure shown is H–C≡C–H.
This is called ethyne (acetylene).
It has a triple bond between the two carbon atoms, making it an alkyne (unsaturated hydrocarbon).
This triple bond contains one sigma (σ) and two pi (π) bonds, making the molecule linear and very reactive.
Industrial use: Ethyne is widely used in oxy-acetylene welding due to its ability to produce a very hot flame on combustion with oxygen.
Its reactivity and flame temperature make it suitable for cutting and joining metals.