Question

Which reagent is used in the Lucas test to distinguish alcohols?

• A. \( \text{ZnCl}_2 + HCl \)
• B. \( KMnO_4 \)
• C. \( NaOH \)
• D. \( H_2SO_4 \)

Hint:

Lucas reagent = Anhydrous \(ZnCl_2\) + concentrated \(HCl\). It helps distinguish primary, secondary, and tertiary alcohols based on the rate of turbidity formation.

Answer 1

The Correct Option is A

Concept: The Lucas test is used to distinguish between primary, secondary, and tertiary alcohols based on their reactivity with Lucas reagent. Lucas reagent is a mixture of: \[ \text{Anhydrous } ZnCl_2 + \text{conc. } HCl \]

Step 1: Understand the reaction. Alcohol reacts with Lucas reagent to form an alkyl chloride. \[ ROH + HCl \xrightarrow{ZnCl_2} RCl + H_2O \]

Step 2: Observation of turbidity.
• 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 \[ \boxed{\text{Anhydrous } ZnCl_2 + \text{ conc. } HCl} \]