Question

Ethane and ethene can be distinguished by using :

• A. Bromine water
• B. Chlorine water
• C. Iodine
• D. HCl

Hint:

The bromine water test is the standard diagnostic test to distinguish between saturated alkanes (no reaction/no color change) and unsaturated alkenes/alkynes (decolorization).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify a chemical reagent that can be used to distinguish between a saturated hydrocarbon, ethane (\(\text{C}_2\text{H}_6\)), and an unsaturated hydrocarbon, ethene (\(\text{C}_2\text{H}_4\)).

Step 2: Key Formula or Approach:
The presence of double or triple carbon-carbon bonds (unsaturation) can be tested using addition reactions with halogens.

Step 3: Detailed Explanation:

• Ethene (\(\text{C}_2\text{H}_4\)): Contains a carbon-carbon double bond (\(\text{C}=\text{C}\)), which is highly reactive. When ethene gas is passed through a reddish-brown solution of bromine water, it undergoes an addition reaction to form a colorless compound, 1,2-dibromoethane:
\[ \text{CH}_2=\text{CH}_2 + \text{Br}_2\text{(aq, reddish-brown)} \to \text{CH}_2\text{Br--CH}_2\text{Br(colorless)} \] This rapid decoloring of bromine water is a classic test for unsaturation.

• Ethane (\(\text{C}_2\text{H}_6\)): Is a saturated alkane containing only single covalent bonds. It is chemically inert to bromine water under normal conditions and does not cause any color change.

• Therefore, bromine water serves as a simple and effective qualitative test to distinguish between ethane and ethene.


Step 4: Final Answer:
Ethane and ethene can be distinguished by using bromine water.