Question 1

What compound is this?

Accepted Answer

Catechol. Green is catechol's signature result with FeCl₃, distinct from phenol's violet. Notice that the first four tests gave no new information at all — they only confirmed "this is some kind of phenol." The FeCl₃ test is what actually identified the compound.

Question 2

What compound is this?

Accepted Answer

β-Naphthol. Purple is its signature FeCl₃ result — distinct from both phenol (violet) and catechol (green). Note: β-naphthol is sparingly soluble in water; dissolve in ethanol before adding FeCl₃ solution.

Question 3

How is phenol identified in the laboratory?

Accepted Answer

A phenol identification test panel — litmus, NaHCO₃, FeCl₃, and bromine water — is used together, since no single test is fully diagnostic on its own; see the full phenol qualitative test methodology in this article.

Question 4

How can phenol be identified by a specific test?

Accepted Answer

Phenol can be identified by the test giving a violet colour with neutral FeCl₃, or a white precipitate with bromine water — both specific to the phenolic –OH group.

Question 5

How can phenol and alcohol be distinguished?

Accepted Answer

Phenol and alcohol can be distinguished by the FeCl₃ test (phenol gives a colour, alcohols don't) and by acidity: phenol reacts with NaOH, ordinary alcohols barely do.

Question 6

What happens when phenol reacts with bromine in CS₂?

Accepted Answer

Unlike bromine water, phenol with bromine in CS₂ at low temperature gives controlled mono-substitution — mainly para-bromophenol with some ortho-bromophenol — rather than the tribromo product, since the non-aqueous medium limits ionisation of phenol.

Question 7

What is the phenol coefficient test?

Accepted Answer

The phenol coefficient test (Rideal-Walker test) is unrelated to structural identification — it measures a disinfectant's germicidal strength against phenol as the reference standard, not phenol's own identity.

Question 8

What is the structure of phenol?

Accepted Answer

Structurally, phenol is a benzene ring carrying one hydroxyl group bonded directly to a ring carbon, giving the formula C₆H₅OH — the –OH's direct attachment to the aromatic system is what defines the compound.

Question 9

What is the molecular formula and molecular weight of phenol?

Accepted Answer

Phenol's formula, C₆H₆O, corresponds to a molecular weight of 94.11 g/mol, calculated from six carbons, six hydrogens, and one oxygen.

Question 10

What is the functional group in phenol?

Accepted Answer

The functional group responsible for phenol's chemistry is a hydroxyl bonded to an aromatic carbon — as opposed to an alcohol's hydroxyl, which sits on a saturated (sp³) carbon instead.

Question 11

What are the pKa values of phenol, ethanol, and a carboxylic acid, and how do their acidities compare?

Accepted Answer

Phenol has a pKa of approximately 9.95, ethanol has a pKa of approximately 15.9, and acetic acid has a pKa of approximately 4.76. Since a lower pKa means a stronger acid, the order of acidity is: carboxylic acid (strongest) > phenol > ethanol (weakest).

Question 12

Is phenol acidic or basic?

Accepted Answer

Phenol is a weak acid: it dissociates enough to react with strong bases such as NaOH, but not enough to react with a weak base like NaHCO₃, which is exactly what the NaHCO₃ test in this article is designed to demonstrate.

Question 13

What is phenol resonance?

Accepted Answer

Resonance in phenol refers to delocalisation of the oxygen's lone pair into the aromatic ring, which concentrates negative charge at the ortho and para positions (carbons 2, 4, and 6) — the same three positions where bromine water substitutes simultaneously.

Question 14

What are the melting and boiling points of phenol?

Accepted Answer

Phenol has a melting point of 40–41 °C and a boiling point of 181.7 °C, with a density of 1.07 g/cm³ at room temperature.

Question 15

How does phenol react with FeCl₃?

Accepted Answer

Warming phenol with neutral aqueous FeCl₃ produces a violet colouration, formed through a ferric phenolate complex — a reaction alcohols and carboxylic acids do not give.

Question 16

What are phenol derivatives?

Accepted Answer

The phenyl urethane derivative, formed by reacting phenol with phenyl isocyanate, melts sharply at ≈126 °C — precise enough to confirm identity against literature or an authentic sample.

Question 17

What is phenol bromination?

Accepted Answer

Phenol's bromination with bromine water proceeds without a catalyst, unlike benzene, and yields 2,4,6-tribromophenol as a white precipitate (m.p. ≈95 °C) — a direct result of resonance-driven ring activation.

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Phenol: Structure, Functional Group, Qualitative Identification Tests, Properties, and Uses

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