701. Which statement correctly describes the general chemical reactivity of simple ethers?
ⓐ. They are highly reactive toward dilute acids and bases at room temperature.
ⓑ. They are comparatively inert toward many common reagents.
ⓒ. They behave like carboxylic acids in water.
ⓓ. They always oxidise primary alcohols to aldehydes.
Correct Answer: They are comparatively inert toward many common reagents.
Explanation: Simple ethers do not contain an \(O-H\) bond, so they do not show the acidic reactions of alcohols or phenols. They are also not easily attacked by dilute acids or bases under ordinary conditions. Their main reactive site is the oxygen lone pair, which can accept a proton in strong acid. Strong hydrogen halides such as \(HI\) or \(HBr\) can cleave ethers on heating.
702. Which reagent does not normally react with simple ethers under ordinary conditions?
ⓐ. Sodium metal
ⓑ. Hot concentrated \(HI\)
ⓒ. Hot concentrated \(HBr\)
ⓓ. Strong acid for protonation
Correct Answer: Sodium metal
Explanation: Sodium metal reacts with alcohols and phenols because they contain an \(O-H\) bond and can release hydrogen gas. Simple ethers do not contain an \(O-H\) bond. Therefore they do not form sodium alkoxides by reaction with sodium metal. Ethers can, however, react with strong hydrogen halides under heating because their oxygen can be protonated.
703. Which structural feature explains why ethers do not evolve \(H_2\) with sodium metal?
ⓐ. They contain no oxygen atom.
ⓑ. They lack acidic \(O-H\) hydrogen.
ⓒ. They contain a carboxyl group.
ⓓ. They contain a phenoxide ion.
Correct Answer: They lack acidic \(O-H\) hydrogen.
Explanation: Sodium metal reacts with compounds that have acidic hydrogen attached to oxygen, such as alcohols and phenols. Ethers have the general structure \(R-O-R'\). Their oxygen is bonded to two carbon groups and has no \(O-H\) bond. Because there is no acidic hydrogen to replace, ethers do not evolve \(H_2\) with sodium.
704. Which pair correctly compares ethanol and ethoxyethane toward sodium metal?
ⓐ. Both evolve \(H_2\) rapidly.
ⓑ. Ethoxyethane evolves \(H_2\), while ethanol does not.
ⓒ. Ethanol evolves \(H_2\), while ethoxyethane does not.
ⓓ. Neither compound contains oxygen.
Correct Answer: Ethanol evolves \(H_2\), while ethoxyethane does not.
Explanation: Ethanol, \(C_2H_5OH\), contains an \(O-H\) bond and reacts with sodium to form sodium ethoxide with hydrogen gas evolution. Ethoxyethane, \(C_2H_5OC_2H_5\), is an ether and has no \(O-H\) bond. It therefore does not show the same sodium-metal reaction. This difference is useful for distinguishing alcohols from ethers.
705. Which equation correctly represents the reaction of ethanol with sodium metal?
ⓐ. \[2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\]
ⓑ. \[C_2H_5OC_2H_5 + 2Na \rightarrow 2C_2H_5ONa\]
ⓒ. \[C_2H_5OH + NaOH \rightarrow C_2H_5Cl + H_2O\]
ⓓ. \[C_2H_5OC_2H_5 + Na \rightarrow C_2H_5I + NaOH\]
Correct Answer: \[2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\]
Explanation: \(\textbf{Reactant type:}\)
Ethanol contains an \(O-H\) bond.
\(\textbf{Role of sodium:}\)
Sodium replaces the acidic hydrogen of the \(O-H\) group.
\(\textbf{Products:}\)
Sodium ethoxide and hydrogen gas are formed.
\(\textbf{Balanced equation:}\)
\[
2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2
\]
\(\textbf{Final Answer:}\)
Ethanol gives sodium ethoxide and hydrogen gas.
706. Which property makes diethyl ether useful as a solvent for Grignard reagents?
ⓐ. It is anhydrous and aprotic, with carbon lone pairs.
ⓑ. It reacts with water to form phenol.
ⓒ. It oxidises Grignard reagents into acids.
ⓓ. It is anhydrous and aprotic, with oxygen lone pairs.
Correct Answer: It is anhydrous and aprotic, with oxygen lone pairs.
Explanation: Grignard reagents are destroyed by water and other proton sources. Dry ether does not contain an \(O-H\) bond, so it does not donate protons to the reagent. Its oxygen lone pairs can help solvate and stabilise the magnesium-containing reagent. This is why dry ether is commonly used as the solvent in Grignard reactions.
707. Why must ether used for Grignard reactions be dry?
ⓐ. Water converts Grignard reagents to hydrocarbons.
ⓑ. Dry ether converts Grignard reagents to hydrocarbons.
ⓒ. Water changes all alcohols into phenols.
ⓓ. Water prevents oxygen from having lone pairs.
Correct Answer: Water converts Grignard reagents to hydrocarbons.
Explanation: Grignard reagents contain a highly basic carbon-magnesium bond. Water supplies a proton and destroys the reagent before it can react with a carbonyl compound. The reaction gives a hydrocarbon, \(R-H\), instead of the desired addition product. Therefore the ether solvent must be dry and the apparatus must be moisture-free.
708. Which equation shows destruction of a Grignard reagent by water?
ⓐ. \[R-OH + H_2O \rightarrow R-O-R + H_2\]
ⓑ. \[R-O-R' + Na \rightarrow R-ONa + R'Na\]
ⓒ. \[R-CHO + H_2O \rightarrow R-COOH + H_2\]
ⓓ. \[R-MgX + H_2O \rightarrow R-H + Mg(OH)X\]
Correct Answer: \[R-MgX + H_2O \rightarrow R-H + Mg(OH)X\]
Explanation: \(\textbf{Grignard character:}\)
The carbon attached to magnesium behaves like a strongly basic centre.
\(\textbf{Effect of water:}\)
Water provides a proton.
\(\textbf{Product from organic group:}\)
The organic group becomes \(R-H\).
\(\textbf{Equation:}\)
\[
R-MgX + H_2O \rightarrow R-H + Mg(OH)X
\]
\(\textbf{Final Answer:}\)
Water destroys the Grignard reagent by protonation.
709. Which compound is the alcohol present in alcoholic beverages?
ⓐ. Methanol
ⓑ. Ethanol
ⓒ. Phenol
ⓓ. Ethoxyethane
Correct Answer: Ethanol
Explanation: Ethanol, \(C_2H_5OH\), is the alcohol present in alcoholic beverages. Methanol, \(CH_3OH\), is highly poisonous and must not be consumed. Phenol is corrosive and structurally different because its \(OH\) group is attached directly to a benzene ring. Ethoxyethane is an ether, not an alcohol.
710. Which statement about ethanol is accurate?
ⓐ. It is a solvent and fuel, but excess intake is harmful.
ⓑ. It is used as solvent and fuel, and is harmless in excess.
ⓒ. It has the formula \(CH_3OH\).
ⓓ. It does not contain an \(O-H\) bond.
Correct Answer: It is a solvent and fuel, but excess intake is harmful.
Explanation: Ethanol is widely used as a solvent because it dissolves many organic substances and mixes with water. It can also be used as a fuel or fuel additive. Although ethanol is the beverage alcohol, excessive consumption is harmful and can cause serious health problems. Its formula is \(C_2H_5OH\), not \(CH_3OH\).
711. Which formula represents ethanol?
ⓐ. \(CH_3OH\)
ⓑ. \(C_2H_5OH\)
ⓒ. \(C_6H_5OH\)
ⓓ. \(C_2H_5OC_2H_5\)
Correct Answer: \(C_2H_5OH\)
Explanation: Ethanol contains two carbon atoms and one hydroxyl group. Its formula is \(C_2H_5OH\). \(CH_3OH\) is methanol, \(C_6H_5OH\) is phenol, and \(C_2H_5OC_2H_5\) is diethyl ether. Correct formula recognition is important because these compounds have very different properties and hazards.
712. Which use is commonly associated with ethanol?
ⓐ. As an antiseptic in suitable concentration
ⓑ. As a source of \(N_2\) gas in diazonium reactions
ⓒ. As a reagent for converting ethers into iodides
ⓓ. As the main product of zinc dust reduction of phenol
Correct Answer: As an antiseptic in suitable concentration
Explanation: Ethanol is used as an antiseptic in suitable aqueous concentration because it can denature proteins and disrupt microbial membranes. Pure ethanol is not always the most effective antiseptic because some water helps the denaturation process. Ethanol is also used as a solvent and fuel. It is not the reagent used for ether cleavage or zinc dust reduction of phenol.
713. Which statement best describes denatured alcohol?
ⓐ. Ethanol made unfit for drinking by toxic additives
ⓑ. Pure phenol dissolved in water
ⓒ. Methanol made unfit for drinking by toxic additives
ⓓ. Ether treated with \(NaOH\)
Correct Answer: Ethanol made unfit for drinking by toxic additives
Explanation: Denatured alcohol is ethanol that has been deliberately made unsuitable for drinking. Substances such as methanol or bitter additives may be added. The purpose is to allow industrial or laboratory use while preventing misuse as a beverage. Denatured alcohol remains unsafe for consumption.
714. Which compound is commonly known for antiseptic use but is corrosive and toxic in concentrated form?
ⓐ. Phenol
ⓑ. Ethane
ⓒ. Dimethyl ether
ⓓ. Sodium chloride
Correct Answer: Phenol
Explanation: Phenol has historical importance as an antiseptic. However, phenol is corrosive and toxic, especially in concentrated form. Its \(OH\) group is directly attached to an aromatic ring, making its properties different from ordinary alcohols. It must therefore be handled carefully.
715. Which use is associated with phenol in chemical industry?
ⓐ. Direct conversion into glucose by yeast
ⓑ. Preparation of table salt
ⓒ. Production of oxygen gas from water only
ⓓ. Making phenol-formaldehyde resins
Correct Answer: Making phenol-formaldehyde resins
Explanation: Phenol is an important starting material in making phenol-formaldehyde resins. These resins are formed by reaction of phenol with formaldehyde under suitable conditions. Phenol is also used in making dyes, drugs, and other aromatic compounds. It is not used for fermentation of glucose or preparation of table salt.
716. Which statement about phenol is correct?
ⓐ. It is less reactive than benzene toward all electrophiles.
ⓑ. It is aromatic and used in resins, dyes, and antiseptics.
ⓒ. It is a simple ether with no \(O-H\) bond.
ⓓ. It is the alcohol present in beverages.
Correct Answer: It is aromatic and used in resins, dyes, and antiseptics.
Explanation: Phenol contains an \(OH\) group directly attached to a benzene ring. It is activated toward electrophilic substitution because of resonance donation from oxygen. Phenol has uses in resin manufacture, dye chemistry, and antiseptic applications, though it is toxic and corrosive. It is not a beverage alcohol or a simple ether.
717. Which compound is historically used as an anaesthetic and is also a volatile ether?
ⓐ. Diethyl ether
ⓑ. Ethanoic acid
ⓒ. Picric acid
ⓓ. Sodium phenoxide
Correct Answer: Diethyl ether
Explanation: Diethyl ether is a volatile ether with the structure \(C_2H_5OC_2H_5\). It has historical importance as an anaesthetic. It is also highly flammable and can form peroxides on storage in air. These hazards limit careless handling and storage.
718. Which formula represents diethyl ether?
ⓐ. \(CH_3OH\)
ⓑ. \(C_3H_7OCH_3\)
ⓒ. \(C_2H_5OC_2H_5\)
ⓓ. \(C_6H_5OH\)
Correct Answer: \(C_2H_5OC_2H_5\)
Explanation: Diethyl ether has two ethyl groups attached to the same oxygen atom. Its formula is \(C_2H_5OC_2H_5\). Ethanol, \(C_2H_5OH\), has an \(O-H\) bond and is an alcohol. Phenol, \(C_6H_5OH\), has \(OH\) directly attached to a benzene ring.
719. Which property makes diethyl ether especially hazardous in storage and use?
ⓐ. It is nonvolatile and nonflammable.
ⓑ. It is highly flammable and can form peroxides.
ⓒ. It is nonflammable and cannot form peroxides during storage.
ⓓ. It turns into sodium phenoxide in air.
Correct Answer: It is highly flammable and can form peroxides.
Explanation: Diethyl ether is very volatile, so it can easily produce flammable vapours. It can also form peroxide impurities when stored for long periods in contact with air. These peroxides can be explosive, especially if concentrated during evaporation or distillation. Therefore diethyl ether must be stored and handled carefully.
720. Which statement correctly matches compound and use or hazard?
ⓐ. Methanol — safe beverage alcohol
ⓑ. Ethanol — solvent, fuel, and antiseptic use
ⓒ. Phenol — harmless food flavour
ⓓ. Diethyl ether — nonflammable inorganic salt
Correct Answer: Ethanol — solvent, fuel, and antiseptic use
Explanation: Ethanol is widely used as a solvent, fuel, and antiseptic in suitable concentration. Methanol is poisonous and must not be consumed. Phenol is corrosive and toxic, though it has industrial and antiseptic importance. Diethyl ether is a flammable organic solvent, not an inorganic salt.
