Question

# An alcohol (A) gives Lucas test within 5 min. 7.4 g of alcohol when treated with sodium metal liberates 1120 mL of H2 at STP. What will be alcohol (A)?

A
CH3(CH2)3OH
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B
CH3CH(OH)CH2CH3
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C
(CH3)3COH
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D
CH3CH(OH)CH2CH2CH3
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Solution

## The correct option is B CH3CH(OH)CH2CH3ROH+Na→RONa+1/2H2↑We have to get molecular mass of alcohol corresponding to half mole of H2 only .No. of moles of H2 = No. of moles of alcohol 112001120=7.4MM⇒MM=74CnH2n+1OH=74→CnH2n+1=7417=57⇒CnH2n=57−1=56i.e.12n+2n=14n=56⇒n=56/14=4Thus molecular formula of (A) is C4H9OH . As (A) gives Lucas test within 5 min., thus 20 alcohol corresponding to molecular formula C4H9OH is CH3CH(OH)CH2CH3 (butan-2-ol).

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