MHT CET · Chemistry · Alcohols Phenols and Ethers

Which from following is called as Lucas reagent?

A Conc. \(\mathrm{HCl}+\mathrm{ZnCl}_2\)
B Neutral \(\mathrm{FeCl}_3\) solution in water
C \(\mathrm{NaNO}_2+\mathrm{HCl}(\) dil. \()\)
D \(\mathrm{CHCl}_3+\mathrm{NaOH}\)

Verified Solution

Answer & Solution

Correct Answer

(A) Conc. \(\mathrm{HCl}+\mathrm{ZnCl}_2\)

Step-by-step Solution

Detailed explanation

Lucas reagent is a mixture of concentrated hydrochloric acid \((\mathrm{HCl})\) and zinc chloride \(\left(\mathrm{ZnCl}_2\right)\). It is used for the differentiation of alcohols based on their reactivity. The test is particularly used to distinguish between primary, secondary, and tertiary alcohols.
- Tertiary alcohols react almost immediately with Lucas reagent to form alkyl chlorides (substitution of the hydroxyl group with a chlorine atom).
- Secondary alcohols react after some time, typically within 5-10 minutes.
- Primary alcohols react very slowly, if at all, and may require heating.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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