601. Liquid P is highly volatile, flammable, historically used as an anaesthetic, and may form peroxides during storage. Liquid Q is an aromatic ether used in fragrance chemistry and undergoes easy ortho-para substitution. P and Q are:
ⓐ. diethyl ether and anisole
ⓑ. anisole and diethyl ether
ⓒ. ethanol and phenol
ⓓ. methanol and ethylene glycol
Correct Answer: diethyl ether and anisole
Explanation: Diethyl ether has a low boiling point and produces highly flammable vapours. Its historical anaesthetic use and peroxide-forming tendency are characteristic identifying features. Anisole contains a methoxy group attached to an aromatic ring. Resonance donation activates that ring and directs substitution toward ortho and para positions. Its odour and aromatic reactivity support its use in fragrance and synthetic chemistry.
602. Assertion: Anisole generally has a higher boiling point than diethyl ether.
Reason: Neither compound forms strong self-associated hydrogen bonds, but anisole has a larger and more polarisable aromatic framework.
ⓐ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓑ. Assertion is true, but Reason is false
ⓒ. Assertion is false, but Reason is true
ⓓ. Both Assertion and Reason are true, and Reason explains Assertion
Correct Answer: Both Assertion and Reason are true, and Reason explains Assertion
Explanation: Both molecules contain ether oxygen but lack an oxygen-hydrogen bond. They therefore cannot donate hydrogen bonds to identical neighbouring molecules. Anisole nevertheless has a greater molar mass and a more polarisable aromatic ring. Its dispersion forces are consequently stronger than those of diethyl ether. The stronger overall attractions raise its boiling point, so the Reason explains the Assertion.
603. Under ordinary aqueous conditions, the acidity order is:
ⓐ. \(\mathrm{ethanol} \gt \mathrm{phenol} \gt \mathrm{ethanoic\ acid} \gt \mathrm{diethyl\ ether}\)
ⓑ. \(\mathrm{phenol} \gt \mathrm{ethanoic\ acid} \gt \mathrm{ethanol} \gt \mathrm{diethyl\ ether}\)
ⓒ. \(\mathrm{ethanoic\ acid} \gt \mathrm{phenol} \gt \mathrm{ethanol} \gt \mathrm{diethyl\ ether}\)
ⓓ. \(\mathrm{diethyl\ ether} \gt \mathrm{ethanol} \gt \mathrm{phenol} \gt \mathrm{ethanoic\ acid}\)
Correct Answer: \(\mathrm{ethanoic\ acid} \gt \mathrm{phenol} \gt \mathrm{ethanol} \gt \mathrm{diethyl\ ether}\)
Explanation: Ethanoic acid forms a carboxylate ion whose negative charge is delocalised over two oxygen atoms. Phenol forms a resonance-stabilised phenoxide ion, but its stabilisation is less effective than that of a carboxylate. Ethanol forms an ethoxide ion in which the negative charge remains largely localised on one oxygen atom. Diethyl ether has no oxygen-hydrogen proton to lose in the same ordinary acid-base sense. The resulting order is carboxylic acid, phenol, alcohol, and then ether.
604. A simple ether is far less acidic than an alcohol in ordinary proton-loss reactions mainly because the ether:
ⓐ. lacks an oxygen-hydrogen proton
ⓑ. contains a positively charged oxygen atom
ⓒ. forms a resonance-stabilised carboxylate ion
ⓓ. releases carbon dioxide on deprotonation
Correct Answer: lacks an oxygen-hydrogen proton
Explanation: An alcohol contains an oxygen-hydrogen bond and can lose that hydrogen as a proton under sufficiently basic conditions. In a simple ether, oxygen is bonded to two carbon groups. There is no hydroxyl proton available for ordinary deprotonation. Removing a carbon-bound hydrogen would require a much stronger base and represents a different chemical process. Ethers therefore do not display the usual acidic behaviour of alcohols or phenols.
605. The acid-base behaviour represented accurately is found in:
| Row | Compound | Aqueous \(\mathrm{NaOH}\) | Aqueous \(\mathrm{NaHCO_3}\) |
|---|
| P | Ethanol | Complete salt formation | Rapid \(\mathrm{CO_2}\) evolution |
| Q | Phenol | No reaction | Rapid \(\mathrm{CO_2}\) evolution |
| R | Diethyl ether | Forms sodium ethoxide | Forms sodium carbonate |
| S | Ethanoic acid | Forms sodium ethanoate | Forms sodium ethanoate with \(\mathrm{CO_2}\) evolution |
ⓐ. Row P
ⓑ. Row Q
ⓒ. Row R
ⓓ. Row S
Correct Answer: Row S
Explanation: Ethanoic acid reacts with sodium hydroxide by neutralisation. It is also stronger than carbonic acid and therefore reacts with sodium bicarbonate to release carbon dioxide. Phenol reacts with sodium hydroxide but not appreciably with bicarbonate under ordinary conditions. Ethanol and diethyl ether do not show the listed reactions with these aqueous bases. Row S correctly reflects the acidity of a carboxylic acid.
606. The approximate \(\mathrm{p}K_a\) values of ethanoic acid, phenol, and ethanol are \(4.8\), \(10\), and \(16\), respectively. Which conclusion follows?
ⓐ. Ethanol is the strongest acid because it has the largest \(\mathrm{p}K_a\)
ⓑ. Ethanoic acid is strongest, followed by phenol and then ethanol
ⓒ. All three compounds have equal acidity
ⓓ. Phenol is stronger than ethanoic acid but weaker than ethanol
Correct Answer: Ethanoic acid is strongest, followed by phenol and then ethanol
Explanation: Acid strength increases as \(\mathrm{p}K_a\) decreases. Ethanoic acid has the lowest value and therefore loses a proton most readily. Phenol has an intermediate value because phenoxide is resonance stabilised. Ethanol has the highest value because ethoxide lacks comparable charge delocalisation. The numerical data therefore support the order ethanoic acid, phenol, and ethanol.
607. Assertion: Phenol is more acidic than ethanol.
Reason: Phenoxide ion is resonance stabilised, whereas the negative charge in ethoxide ion remains mainly localised on oxygen.
ⓐ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓑ. Assertion is true, but Reason is false
ⓒ. Both Assertion and Reason are true, and Reason explains Assertion
ⓓ. Assertion is false, but Reason is true
Correct Answer: Both Assertion and Reason are true, and Reason explains Assertion
Explanation: Acid strength is closely related to the stability of the conjugate base. Deprotonation of phenol gives phenoxide ion, whose negative charge can be delocalised into the aromatic ring. Deprotonation of ethanol gives ethoxide ion, where the charge remains concentrated mainly on oxygen. Greater conjugate-base stabilisation favours proton loss from phenol. The Reason therefore provides the correct explanation for the Assertion.
608. Three compounds X, Y, and Z give the following observations.
X releases carbon dioxide with aqueous sodium bicarbonate.
Y dissolves in aqueous sodium hydroxide and gives a coloured complex with neutral ferric chloride but does not react with bicarbonate.
Z shows no reaction with aqueous sodium hydroxide and releases no hydrogen with sodium metal.
The compounds X, Y, and Z are respectively:
ⓐ. phenol, ethanoic acid, diethyl ether
ⓑ. ethanol, phenol, diethyl ether
ⓒ. ethanoic acid, ethanol, anisole
ⓓ. ethanoic acid, phenol, diethyl ether
Correct Answer: ethanoic acid, phenol, diethyl ether
Explanation: Bicarbonate effervescence identifies X as a carboxylic acid such as ethanoic acid. Y behaves as phenol because it forms sodium phenoxide with hydroxide and a coloured complex with ferric chloride. Its failure to release carbon dioxide from bicarbonate is consistent with its weaker acidity. Z lacks a hydroxyl proton and does not undergo the sodium-metal reaction of alcohols or phenols. Diethyl ether therefore fits the final observation set.
609. A dry sample containing only phenol and ethanol releases (0.125,\mathrm{mol}) of hydrogen when treated with excess sodium metal. A separate identical sample consumes (0.075,\mathrm{mol}) of sodium hydroxide. What is the mole percentage of phenol in the mixture?
ⓐ. (20%)
ⓑ. (25%)
ⓒ. (30%)
ⓓ. (40%)
Correct Answer: (30%)
Explanation: ( \textbf{Total hydroxyl compounds from hydrogen evolution:} )
Both phenol and ethanol react with sodium according to the general relation
[
\mathrm{2ROH+2Na\rightarrow2RONa+H_2}
]
Two moles of hydroxyl compound therefore produce one mole of hydrogen.
[
n(\text{phenol})+n(\text{ethanol})=2n(\mathrm{H_2})
]
[
=2\times0.125
]
[
=0.250,\mathrm{mol}
]
( \textbf{Phenol amount from sodium hydroxide:} )
Phenol reacts with aqueous sodium hydroxide in a (1:1) mole ratio, whereas ethanol does not react appreciably.
[
n(\text{phenol})=n(\mathrm{NaOH})
]
[
n(\text{phenol})=0.075,\mathrm{mol}
]
( \textbf{Mole percentage of phenol:} )
[
\text{Mole percentage}
=
\frac{0.075}{0.250}\times100
]
[
=30%
]
( \textbf{Final answer:} ) Phenol constitutes (30%) of the mixture by amount. Hydrogen evolution determines the total amount of hydroxyl-containing compounds, while sodium hydroxide selectively determines the phenol amount.
610. A graph has conjugate-base stabilisation on the horizontal axis and \(\mathrm{p}K_a\) on the vertical axis. For a related series of acids, the expected general trend is:
ⓐ. \(\mathrm{p}K_a\) rises because stabilisation weakens every acid
ⓑ. \(\mathrm{p}K_a\) remains constant regardless of structure
ⓒ. acidity disappears when the conjugate base is stabilised
ⓓ. greater conjugate-base stabilisation lowers \(\mathrm{p}K_a\)
Correct Answer: greater conjugate-base stabilisation lowers \(\mathrm{p}K_a\)
Explanation: A more stable conjugate base is formed more readily from its parent acid. Proton loss therefore becomes thermodynamically more favourable. Greater acid strength corresponds to a larger acid-dissociation constant, \(\mathrm{K_a}\). Since \(\mathrm{p}K_a=-\log K_a\), a larger \(\mathrm{K_a}\) gives a smaller \(\mathrm{p}K_a\). The graph should consequently slope downward as conjugate-base stabilisation increases.
611. Four separately labelled samples are known to be ethanoic acid, phenol, ethanol, and diethyl ether. Which procedure can identify all four while avoiding interference between reagents?
ⓐ. Use fresh portions with aqueous (\mathrm{NaHCO_3}), neutral (\mathrm{FeCl_3}), and sodium metal on dry fresh portions
ⓑ. Add aqueous (\mathrm{NaOH}) to one portion, then add sodium metal directly to the same aqueous mixture
ⓒ. Use neutral (\mathrm{FeCl_3}), dilute (\mathrm{HCl}), and aqueous (\mathrm{NaCl}) on fresh portions
ⓓ. Add bromine water to one portion and identify all four compounds only from the extent of decolourisation
Correct Answer: Use fresh portions with aqueous (\mathrm{NaHCO_3}), neutral (\mathrm{FeCl_3}), and sodium metal on dry fresh portions
Explanation: Ethanoic acid is identified by carbon dioxide evolution with aqueous sodium bicarbonate. Phenol is identified on another portion by its characteristic colour with neutral ferric chloride. After those two compounds have been assigned, ethanol and diethyl ether remain. Sodium metal is then used only on dry fresh portions: ethanol releases hydrogen because it contains an oxygen-hydrogen bond, whereas diethyl ether does not. Adding sodium metal to an aqueous mixture would cause sodium to react with water and would make the observation unsafe and chemically uninformative. Bromine-water decolourisation alone is also insufficient because it does not provide a distinct response for every compound. Separate portions preserve the selectivity of each observation and prevent one reagent from interfering with the next.
612. The reaction represented accurately is:
| Row | Compound and reagent | Principal reaction |
|---|
| P | Phenol with aqueous \(\mathrm{NaHCO_3}\) | Rapid evolution of \(\mathrm{CO_2}\) |
| Q | Diethyl ether with one equivalent of hot \(\mathrm{HI}\) | Formation of iodoethane and ethanol |
| R | Ethanol with neutral \(\mathrm{FeCl_3}\) | Violet coordination complex |
| S | Anisole with aqueous \(\mathrm{NaOH}\) | Formation of sodium phenoxide and methanol |
ⓐ. Row P
ⓑ. Row Q
ⓒ. Row R
ⓓ. Row S
Correct Answer: Row Q
Explanation: Hot hydrogen iodide protonates the oxygen atom of diethyl ether. Iodide then attacks an ethyl carbon and cleaves one carbon-oxygen bond. With one equivalent of \(\mathrm{HI}\), the initial products are iodoethane and ethanol. Phenol does not ordinarily release carbon dioxide from bicarbonate. Ethanol does not give the characteristic phenolic ferric chloride colour, and anisole is not cleaved by aqueous sodium hydroxide under ordinary conditions.
613. Three compounds X, Y, and Z give the following observations.
X changes acidified dichromate from orange to green and can be dehydrated to an alkene.
Y dissolves in aqueous sodium hydroxide and gives a violet colour with neutral ferric chloride.
Z is largely unchanged by aqueous sodium hydroxide but is cleaved on heating with concentrated hydrogen iodide.
Which assignment is correct?
ⓐ. X is phenol, Y is an ether, and Z is an alcohol
ⓑ. X is an ether, Y is an alcohol, and Z is phenol
ⓒ. X is phenol, Y is an alcohol, and Z is a carboxylic acid
ⓓ. X is an alcohol, Y is phenol, and Z is an ether
Correct Answer: X is an alcohol, Y is phenol, and Z is an ether
Explanation: Oxidation by acidified dichromate and dehydration to an alkene are characteristic reactions of suitable alcohols. Solubility in sodium hydroxide together with a ferric chloride colour identifies a phenolic hydroxyl group. A simple ether lacks an acidic hydroxyl proton and remains largely unchanged with aqueous hydroxide. Strong hydrogen iodide can protonate and cleave the ether linkage. The three observations distinguish the functional groups by reaction type rather than by appearance alone.
614. A student claims that because ethanol reacts with hydrogen bromide to form bromoethane, phenol should react equally readily with hydrogen bromide to form bromobenzene. Evaluate the claim.
ⓐ. phenol's aryl carbon–oxygen bond has partial double-bond character and resists substitution
ⓑ. The claim is correct because every hydroxyl compound reacts identically with hydrogen bromide
ⓒ. The claim is correct only because phenoxide ion is a strong leaving group
ⓓ. The claim is incorrect because phenol contains no oxygen-hydrogen bond
Correct Answer: phenol's aryl carbon–oxygen bond has partial double-bond character and resists substitution
Explanation: In ethanol, the hydroxyl group is attached to an \(\mathrm{sp^3}\)-hybridised carbon. Protonation can convert the hydroxyl group into a better leaving group, allowing substitution by bromide. In phenol, the carbon-oxygen bond is attached directly to an aromatic \(\mathrm{sp^2}\) carbon. Resonance gives this bond partial double-bond character and strengthens it. Phenol therefore does not form bromobenzene through the ordinary alcohol-to-haloalkane pathway.
615. Equal samples of propan-1-ol, propan-2-ol, tert-butanol, and phenol are treated with Lucas reagent at room temperature. Which observation is most appropriate?
ⓐ. phenol reacts immediately; tert-butanol is delayed; both propanols remain clear
ⓑ. all four react immediately with no difference in reaction time
ⓒ. tert-butanol immediate; propan-2-ol delayed; propan-1-ol and phenol initially clear
ⓓ. propan-1-ol reacts immediately, propan-2-ol is delayed, and tert-butanol plus phenol remain clear
Correct Answer: tert-butanol immediate; propan-2-ol delayed; propan-1-ol and phenol initially clear
Explanation: Lucas reagent converts suitable alcohols into insoluble alkyl chlorides. Tertiary alcohols react rapidly because they can form relatively stable tertiary carbocations. Secondary alcohols react more slowly, while ordinary primary alcohols show little or no immediate turbidity at room temperature. Phenol does not undergo the normal Lucas substitution because its aryl carbon-oxygen bond is resistant to cleavage. The observation pattern separates alcohol classes while also distinguishing phenol from an aliphatic alcohol.
616. Assertion: Concentrated sulfuric acid can dehydrate an alcohol, whereas concentrated hydrogen iodide can cleave an ether.
Reason: Both processes involve protonation of oxygen, but the subsequent bond-breaking pathway depends on the substrate and reagent present.
ⓐ. Both Assertion and Reason are true, but Reason does not explain Assertion
ⓑ. Both Assertion and Reason are true, and Reason explains Assertion
ⓒ. Assertion is true, but Reason is false
ⓓ. Assertion is false, but Reason is true
Correct Answer: Both Assertion and Reason are true, and Reason explains Assertion
Explanation: Alcohol dehydration begins when the hydroxyl oxygen is protonated, making water a better leaving group. Loss of water and removal of a beta proton can then produce an alkene. Ether cleavage also begins with protonation of oxygen, but a halide ion attacks or assists carbon-oxygen bond breaking. The products and mechanisms differ because an alcohol contains an oxygen-hydrogen group, whereas an ether contains two carbon groups attached to oxygen. The Reason therefore explains the common first step and the different reaction outcomes.
617. Use the graph description below. Equal molar samples of ethanol, phenol, and diethyl ether are separately treated under the standard mild acidified-dichromate conditions used to test oxidisable alcohols. Product concentration is plotted against time. Which curve should rise most clearly?
ⓐ. The curve for ethanol oxidation products
ⓑ. The curve for ordinary ether-cleavage products
ⓒ. The curve for sodium phenoxide
ⓓ. All three curves should rise identically
Correct Answer: The curve for ethanol oxidation products
Explanation: Ethanol is a primary alcohol and is readily oxidised under standard acidified-dichromate test conditions. Its oxidation products therefore increase in concentration as ethanol is consumed. Diethyl ether does not undergo the ordinary alcohol oxidation reaction because it lacks a hydroxyl-bearing carbon. Phenol has different oxidation chemistry and is not interpreted by the standard primary-alcohol dichromate test in the same way. The ethanol curve should consequently show the clearest rise.
618. In cleavage of an aryl alkyl ether by hydrogen iodide, the bond that normally breaks is the ______ bond.
ⓐ. aromatic carbon-carbon
ⓑ. aromatic carbon-hydrogen
ⓒ. aryl-oxygen
ⓓ. alkyl-oxygen
Correct Answer: alkyl-oxygen
Explanation: Hydrogen iodide first protonates the ether oxygen. Iodide then attacks the alkyl carbon when that carbon is suitable for substitution. The aryl-oxygen bond is strengthened by resonance and is attached to an \(\mathrm{sp^2}\)-hybridised aromatic carbon. Ordinary backside displacement at that aromatic carbon is unfavourable. Cleavage therefore occurs at the alkyl-oxygen bond, producing phenol and an alkyl iodide.
619. The row that accurately distinguishes the dominant reaction classes of an alcohol, phenol, and ether is:
| Row | Alcohol | Phenol | Ether |
|---|
| P | Only aromatic substitution | Only dehydration | Only oxidation |
| Q | No reaction with oxidants | Ordinary Lucas substitution | Reaction with bicarbonate |
| R | Oxidation or dehydration | Acid-base reaction and rapid ring substitution | Cleavage by strong hydrogen halides |
| S | Only salt formation | Only carbonyl reduction | Hydrogen evolution with sodium |
ⓐ. Row P
ⓑ. Row R
ⓒ. Row Q
ⓓ. Row S
Correct Answer: Row R
Explanation: Suitable alcohols can undergo oxidation, dehydration, substitution, and esterification. Phenol shows weak acidic behaviour and reacts rapidly in electrophilic substitution because its aromatic ring is activated by the hydroxyl group. Simple ethers are relatively inert toward many ordinary reagents but can be cleaved by strong hydrogen halides. They lack an oxygen-hydrogen bond and do not release hydrogen with sodium in the manner of alcohols. Row R correctly captures the characteristic reaction families.
620. Ethene can be converted into ethanal using:
ⓐ. acid hydration, then controlled oxidation
ⓑ. Bromine water, followed by aqueous sodium bicarbonate
ⓒ. Concentrated hydrogen iodide, followed by sodium metal
ⓓ. Neutral ferric chloride, followed by concentrated nitric acid
Correct Answer: acid hydration, then controlled oxidation
Explanation: Acid-catalysed hydration adds water across the double bond of ethene. Because ethene is symmetrical, the product is ethanol. Controlled oxidation of the primary alcohol then removes two hydrogen atoms and forms ethanal. Stronger or prolonged oxidation could continue to ethanoic acid, so the oxidation conditions must be controlled. The sequence tracks the change from alkene to alcohol and then to aldehyde without changing the two-carbon skeleton.
