Benzene and chlorobenzene are both miscible liquids at room temperature. Because they possess distinct boiling points, fractional distillation is the standard industrial and laboratory method used to separate them. The component with the lower boiling point vaporizes first, allowing for the collection of purified fractions through condensation.
12
Identify compound A, given that its reduction yields B, which reacts with CHCl3 and alcoholic KOH to form C, and subsequent hydrolysis of C produces aniline.
Nitrobenzene is reduced to aniline (B). Aniline reacts with chloroform and alcoholic KOH (carbylamine reaction) to form phenyl isocyanide (C). Hydrolysis of phenyl isocyanide typically yields aniline and formic acid. This sequence confirms that nitrobenzene is the starting material. The carbylamine reaction is a diagnostic test for primary amines, confirming the presence of the amino group derived from the nitro precursor.
13
Which reagent is utilized to convert carboxylic acids into their corresponding esters?
Fischer esterification is the process of converting a carboxylic acid into an ester using an alcohol in the presence of an acid catalyst, such as dry HCl or concentrated sulfuric acid. The acid catalyst protonates the carbonyl oxygen, making the carbon more electrophilic for nucleophilic attack by the alcohol. LiAlH4 is a strong reducing agent that would reduce the acid to an alcohol, not an ester.
14
Which of the following compounds yields benzoic acid upon oxidation?
The oxidation of the benzylic carbon atom in benzyl chloride (C6H5CH2Cl) results in the formation of benzoic acid. The benzylic position is susceptible to oxidation by strong oxidizing agents. In contrast, chlorobenzene lacks a benzylic alkyl group, and chlorotoluene would yield chlorobenzoic acid rather than benzoic acid. This reaction is a standard method for converting alkyl-substituted benzenes into carboxylic acids.
15
What is the correct IUPAC nomenclature for the compound C2H5CONH2?
The chemical formula C2H5CONH2 represents a three-carbon amide chain (CH3CH2CONH2). In IUPAC nomenclature, the parent alkane for a three-carbon chain is propane. Replacing the terminal 'e' with 'amide' gives the name propanamide. This compound is derived from propanoic acid, where the hydroxyl group is replaced by an amino group.
16
In which of the following acids is lead metal soluble?
Lead is generally resistant to many acids due to the formation of insoluble surface layers (like PbCl2 or PbSO4). However, it dissolves readily in nitric acid (HNO3) because lead nitrate is highly soluble in water, and the oxidizing nature of the nitrate ion facilitates the oxidation of lead metal to lead ions.
17
Which metal is primarily utilized in the production of photographic films due to its light-sensitive properties?
Photographic films rely on the light sensitivity of silver halides, such as silver bromide (AgBr). When exposed to light, silver ions are reduced to metallic silver, creating the latent image. Silver is the essential metal used in traditional film photography for this purpose.
18
Which of the following metals is typically found in its native or free state in nature?
Gold is a noble metal with very low chemical reactivity, which prevents it from easily forming compounds with oxygen or sulfur under standard environmental conditions. Consequently, it is frequently found in its elemental, or 'free', state in nature. In contrast, metals like sodium, potassium, and calcium are highly reactive and are almost exclusively found in nature as stable ionic compounds, such as chlorides or carbonates.
19
Which of the following metals is considered the most malleable?
Malleability is the ability of a substance to be hammered or rolled into thin sheets without breaking. Gold is the most malleable of all metals, allowing it to be beaten into extremely thin leaves, often only a few micrometers thick.
20
Which of the following temperatures represents a plausible melting point for iron?
Iron is a transition metal with a high melting point due to strong metallic bonding. The actual melting point of pure iron is approximately 1538°C. Among the provided choices, 1500°C is the only value that accurately reflects the high thermal energy required to transition iron from solid to liquid.
