Explain the mechanism of acid catalysed dehydration of ethanol to yield the corresponding alkene.
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Alcohols - ISC Class 12 Chemistry Questions with Answers, Page 2
39 past-paper questions on Alcohols from ISC Class 12 Chemistry papers (2027-2018), newest first, in full. Questions 21-39 are on this page, 20 to a page. Tap "Show answer" under a question to see its answer.
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(i)[1.0]
Arrange the following alcohols in order of decreasing activity towards Lucas’ reagent.
2-butanol, 2-methyl-2-propanol and 1-butanol
(ii)[1.0]
Ethanol has a higher boiling point than methoxymethane. Justify the statement.
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Identify the compounds [A], [B] and [C] in each of the following reactions.
(a)[1.5]
$\text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{PCl}_5} [\text{A}] \xrightarrow{\text{KCN}} [\text{B}] \xrightarrow{\text{H}_3\text{O}^+} \text{C}_2\text{H}_5\text{COOH} \xrightarrow{\text{NH}_3} [\text{C}]$
(b)[1.5]
$\text{C}_6\text{H}_5\text{OH} \xrightarrow{\text{Zn/dust}} [\text{A}] \xrightarrow[\text{anhy. }\text{AlCl}_3]{\text{CH}_3\text{Cl}} [\text{B}] \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 + \text{H}_2\text{SO}_4]{[\text{O}]} [\text{C}]$
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Convert the following by giving chemical equations for each.
(i)[1.0]
Ethyl bromide to diethyl ether
(ii)[1.0]
Phenol to salicylaldehyde
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(i)[1.0]
Write a chemical test to distinguish between ethanol and phenol.
(ii)[1.0]
Give a chemical reaction to convert acetaldehyde into secondary propyl alcohol.
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Choose the appropriate word(s) from the bracket [lead poisoning, zero, phosgene, dependent, cancer, independent, diethyl ether, first, ethyl carbonate, ethene]:
The dehydration of ethyl alcohol with conc. $\text{H}_2\text{SO}_4$ at $140^\circ\text{C}$ mainly yields ____ while at $170^\circ\text{C}$ the main product formed is ____.
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Fill in the blanks by choosing the appropriate word(s) from those given in the brackets:
[decreases, $\text{CN}^-$ ion, activation energy, catalyst, two, $\text{Fe}^{2+}$ ion, carbon, lattice energy, enzyme, five, double, halogen, triple, increases]
In case of alcohols, as the carbon chain length increases, the boiling point ____ and the solubility in water ____.
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How will the following be obtained? (Give chemical equation)
(a)[1.0]
Picric acid from phenol
(b)[1.0]
Ethanol from formaldehyde
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Account for the following:
(i)[1.0]
Phenol is a stronger acid than aliphatic alcohols.
(ii)[1.0]
Ethanol gives iodoform reaction whereas methanol does not give iodoform reaction.
(iii)[1.0]
Ethers should not be distilled to dryness.
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An organic compound [A] $\text{C}_2\text{H}_6\text{O}$, on heating with conc. $\text{H}_2\text{SO}_4$ at $413\text{ K}$ gives a neutral compound [B] $\text{C}_4\text{H}_{10}\text{O}$. Compound [B] on treatment with $\text{PCl}_5$ gives a product, which on subsequent treatment with $\text{KCN}$ yields compound [C] $\text{C}_3\text{H}_5\text{N}$. Compound [C] on hydrolysis gives an acid [D] $\text{C}_3\text{H}_6\text{O}_2$. Identify the compounds [A], [B], [C] and [D].
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How will the following be obtained? (Give chemical equation)
(a)[1.0]
Ethanol from Grignard’s reagent.
(b)[1.0]
Diethyl ether from sodium ethoxide.
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An organic compound ‘A’ on treatment with aq. $\text{KCN}$ produces compound ‘B’. Compound ‘B’ on reduction with $\text{Na}/\text{C}_2\text{H}_5\text{OH}$ gives compound ‘C’ with molecular formula $\text{C}_2\text{H}_7\text{N}$. Compound ‘C’ reacts with $\text{NaNO}_2$ and $\text{HCl}$ to form compound ‘D’. Compound ‘D’ on treatment with acetic acid in presence of conc. $\text{H}_2\text{SO}_4$ produces a sweet smelling compound ‘E’.
(i)[2.0]
Identify the compounds ‘A’ to ‘E’.
(ii)[1.0]
Name the reaction for the formation of compound ‘E’ from compound ‘D’.
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Write the chemical equations for the dehydration of ethanol with conc. $\text{H}_2\text{SO}_4$ at $140^\circ\text{C}$ and $170^\circ\text{C}$.
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The optically active compound is:
- (a)Butan-1-ol
- (b)Butan-2-ol
- (c)Propan-1-ol
- (d)2-methyl-propan-1-ol
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Ethyl alcohol when reacts with PCl5 gives a compound (A). When compound (A) is treated with alc. KOH, compound (B) is formed along with KCl and H2O.
(i)
The compound (A) is:
- (a)C2H4Cl2
- (b)CH3CHO
- (c)C2H5Cl
- (d)CH3OH
(ii)
The compound (B) is:
- (a)C2H2
- (b)C2H4
- (c)C2H6
- (d)C2H5OH
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Boiling point of ethyl alcohol is greater than diethyl ether due to:
- (a)Vander Waals forces
- (b)London forces
- (c)Polarity
- (d)Hydrogen bonding
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An unknown alcohol is treated with Lucas reagent to determine whether the alcohol is primary, secondary or tertiary.
(i)
Which alcohol reacts fastest and by what mechanism?
- (a)Tertiary alcohol by SN2
- (b)Secondary alcohol by SN1
- (c)Tertiary alcohol by SN1
- (d)Secondary alcohol by SN2
(ii)
What is the chemical composition of the Lucas reagent used above?
- (a)Anhydrous zinc chloride in concentrated HCl
- (b)Anhydrous aluminium chloride in concentrated HCl
- (c)Anhydrous lead chloride in concentrated HCl
- (d)Anhydrous barium chloride in concentrated HCl
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Reaction between acetone and methyl magnesium chloride, followed by hydrolysis will give:
- (a)tert-butyl alcohol
- (b)iso-butyl alcohol
- (c)iso-propyl alcohol
- (d)sec-butyl alcohol
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Write the mechanism of acid dehydration of ethanol to yield ethene.
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