Question

Which reagent is used in the Lucas test to distinguish between primary, secondary, and tertiary alcohols?

• A. Dilute HCl
• B. Concentrated HCl and \(ZnCl_2\)
• C. \(NaOH\)
• D. \(KMnO_4\)

Hint:

Lucas reagent = \(ZnCl_2 +\) concentrated HCl. Tertiary alcohols react fastest because they form the most stable carbocations.

Answer 1

The Correct Option is B

Concept: The Lucas test is used to distinguish between primary, secondary, and tertiary alcohols based on their rate of reaction with Lucas reagent. Lucas reagent consists of: \[ \text{Concentrated } HCl + ZnCl_2 \]

Step 1: Role of Lucas reagent. The reagent converts alcohols into alkyl chlorides. \[ R-OH + HCl \rightarrow R-Cl + H_2O \]

Step 2: Observation in the Lucas test.
• Tertiary alcohol → Immediate turbidity
• Secondary alcohol → Turbidity after few minutes
• Primary alcohol → No turbidity at room temperature Thus, the reagent used in the Lucas test is: \[ \boxed{\text{Concentrated HCl and } ZnCl_2} \]