Carbon & its Compounds - 2 - UPSC MCQ

Hydrolysis of an ester with alkali is called saponification reaction.

When ethanol is heated with concentrated sulphuric acid at 443 K, dehydration takes place and ethene is formed. In this reaction concentrated sulphuric acid acts as a dehydrating agent.
CH₃-CH₂-OH → (H₂SO₄ + heat) → CH₂=CH₂ + H₂O

Compounds of carbon and hydrogen containing double or triple bonds in the molecule are called unsaturated hydrocarbons.

Methanol causes blindness and even death. It is also known as denatured alcohol.

The smallest alkyne contains two carbon atoms with a triple bond between them.

CH₃CH₂OH is present in alcoholic drinks. It is known as ethanol which is prepared by fermentation of sugar (molasses).

- Straight chain compounds are one of the types of isomers of organic compounds in which there is no substituent attached on the parent hydrocarbon chain.
- Let’s have a look at the given compounds in the question.
- First compound is,

- Now, we need to count the total number of carbon atoms present in this compound. The total number of carbon atoms present in this compound is five. Also, the longest continuous hydrocarbon chain present in the compound is pentane only. There are no substituents attached on the chain. Therefore, this is a straight chain compound.
- Second compound is,

- In this compound, the total number of carbon atoms is six and but, the longest continuous hydrocarbon chain is pentane. There is one methyl substituent attached to the second carbon atom in the chain. Therefore, this compound is not a straight chain compound. This compound is a branched chain compound, iso-hexane.
- Third compound is,

- In this compound, the total number of carbon atoms is six and also, the longest continuous hydrocarbon chain is hexane. There are no substituents attached on the chain. Therefore, this compound is a straight chain compound, n-hexane.
- Fourth compound is,

- In this compound, the total number of carbon atoms is six and also, the longest continuous hydrocarbon chain is hexane. There are no substituents attached on the chain. Therefore, this compound is a straight chain compound, n-hexane.
- Therefore, compound (B) iso-hexane is not a straight chain compound.

Therefore, the correct option is option (d).

Note:
Don’t get confused that the term ‘straight’ indicates the number of carbon present in one line. That is a common mistake. Straight chain means number of carbon atoms forming a long continuous chain. It can be represented in many ways, zig-zag, or vertically, or horizontally, etc. Be thorough with this minor concept.

C₂H₅OH + 2Na → C₂H₅ONa + H₂

Compounds (a), (b) and (c) are saturated hydrocarbons but compound (d) is unsaturated. Compounds of the same homologous series have the same general formula.

The atoms other than hydrogen and carbon are called heteroatoms.

After sharing four electrons with four univalent atoms, carbon has 6 + 4 = 10 electrons.
Neon also contains 10 electrons

Vinegar is a diluted solution of acetic acid in water. It’s composition is 5% - 8% of acetic acid in water.

It contains a total of three carbon atoms with an aldehyde group. Propane + al = propanal.

The equation for the reaction between sodium and ethanol can be written as:

2CH₃​CH₂​OH+2Na→2CH_3​CH_2​ONa+H_2​

Therefore, the products formed are sodium ethoxide and hydrogen

It is well known that mineral acids are completely ionised while carboxylic acids are partially ionised

Organic compounds have covalent bonding in their molecules. Such compounds are poor conductors of electricity and have low boiling points.

• Chlorine is a highly reactive element that readily reacts with unsaturated hydrocarbons, such as alkenes and alkynes, to form addition products.


• However, when it comes to saturated hydrocarbons, chlorine can only react in the presence of sunlight.


• When chlorine reacts with saturated hydrocarbons, a substitution reaction takes place.


• The reaction involves the replacement of one or more hydrogen atoms in the hydrocarbon molecule with chlorine atoms.


• The presence of sunlight is essential for this reaction to occur because it provides the necessary energy to break the chlorine molecule into highly reactive chlorine radicals.


• These chlorine radicals then react with the saturated hydrocarbon, breaking one or more carbon-hydrogen bonds and replacing the hydrogen atoms with chlorine atoms.


• This reaction is known as photochemical chlorination.


• In the absence of sunlight, chlorine does not have sufficient energy to undergo homolytic cleavage and form chlorine radicals, thus preventing the reaction with saturated hydrocarbons.

  There are 7 covalent bonds in the compound.

The correct answer is: (d) Butane and 2-methylpropane

• Isomers are compounds that have the same molecular formula but different structural arrangements.
• Butane (C_₄H₁_₀) and 2-methylpropane (C_₄H_₁₀) share the same molecular formula (C_₄H_₁₀) but differ in their structural arrangement:
  • Butane is a straight-chain hydrocarbon.
  • 2-methylpropane (isobutane) is a branched-chain hydrocarbon.

This makes them structural isomers of each other