Question

What is the number of moles of ethane obtained from 2n moles of bromomethane using 2n moles of sodium atoms in dry ether medium?

• A. 4n
• B. 3n
• C. 2n
• D. n

Hint:

The Wurtz reaction is a coupling reaction where two alkyl halide molecules combine to form a longer alkane chain, with 2 moles of alkyl halide producing 1 mole of alkane. The reaction requires sodium metal in a dry ether solvent.

Answer 1

The Correct Option is A

Concept:
When an alkyl halide reacts with sodium metal in dry ether, the reaction is called the Wurtz reaction. In this reaction, two alkyl groups combine to form a higher alkane. General reaction: \[ 2R-X + 2Na \xrightarrow{\text{dry ether R-R + 2NaX \] where:

• $R$ = alkyl group
• $X$ = halogen

Step 1: Write reaction for bromomethane
Given alkyl halide is bromomethane: \[ CH_3Br \] Applying Wurtz reaction: \[ 2CH_3Br + 2Na \xrightarrow{\text{dry ether C_2H_6 + 2NaBr \] The product formed is ethane.
Step 2: Use mole ratio
From balanced equation: \[ 2 \text{ moles of } CH_3Br \longrightarrow 1 \text{ mole of } C_2H_6 \] Also: \[ 2 \text{ moles of Na are required} \]
Step 3: Given quantities
Initial moles: \[ 2n \text{ moles of } CH_3Br \] \[ 2n \text{ moles of Na} \] These are in exact stoichiometric ratio.
Step 4: Calculate moles of ethane formed
Since: \[ 2 \text{ moles } CH_3Br \rightarrow 1 \text{ mole } C_2H_6 \] Therefore: \[ 2n \text{ moles } CH_3Br \rightarrow n \text{ moles } C_2H_6 \]
Step 5: Final Answer
The number of moles of ethane obtained is: \[ \boxed{n} \] Quick Tip:
In Wurtz reaction, two molecules of alkyl halide always combine to give one molecule of alkane.