Question

(A) (i) Define a homologous series of carbon compounds.
(ii) Why is the melting and boiling points of \(C_4H_8\) higher than that of \(C_3H_6\) or \(C_2H_4\)?
(iii) Why do we NOT see any gradation in chemical properties of a homologous series compounds?
(iv) Write the name and structures of (i) aldehyde and (ii) ketone with molecular formula \(C_3H_6O\).

OR

(B) (i) Write the name and structure of an organic compound ‘X’ having two carbon atoms in its molecule and its name is suffixed with ‘-ol’.
(ii) What happens when ‘X’ is heated with excess concentrated sulphuric acid at 443 K? Write chemical equation for the reaction stating the conditions for the reaction. Also state the role played by concentrated sulphuric acid in the reaction.
(iii) Name and draw the electron dot structure of hydrocarbon produced in the above reaction.

Answer 1

(A) i. A homologous series is defined as a group of organic compounds that share a common general formula, exhibit similar chemical properties, and where each successive member differs by a \(-\text{CH}_2\) unit. Examples include alkanes (\(\text{C}_n\text{H}_{2n+2}\)), alkenes (\(\text{C}_n\text{H}_{2n}\)), and alcohols (\(\text{C}_n\text{H}_{2n+1}\text{OH}\)).
ii. The functional group, which remains constant within a homologous series, dictates the chemical properties. Consequently, compounds within the same series display comparable reactivity without any gradual change in chemical properties.
iii. Aldehyde: Propanal
  Structure: \(\text{CH}_3\text{-CH}_2\text{-CHO}\)
   Ketone: Propanone (acetone) 
   Structure: \(\text{CH}_3\text{-CO-CH}_3\)

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(B) i. Solution: The identified compound is ethanol.  
   Structure: \(\text{CH}_3\text{-CH}_2\text{-OH}\)

ii. Upon heating ethanol (\(\text{CH}_3\text{-CH}_2\text{-OH}\)) with concentrated \(\text{H}_2\text{SO}_4\) at 443 K, dehydration occurs, resulting in the formation of ethene (\(\text{C}_2\text{H}_4\)).
  Reaction: \(\text{CH}_3\text{-CH}_2\text{-OH} \rightarrow \text{C}_2\text{H}_4 + \text{H}_2\text{O}\)
  Conditions: 443 K temperature, with excess concentrated \(\text{H}_2\text{SO}_4\)

iii. The hydrocarbon produced by this reaction is ethene (\(\text{C}_2\text{H}_4\)).