201. Which interaction mainly explains the unusually high boiling point of ethanol compared with ethane?
ⓐ. Intermolecular hydrogen bonding
ⓑ. Ionic bonding between molecules
ⓒ. Metallic bonding in liquid ethanol
ⓓ. Covalent network formation
Correct Answer: Intermolecular hydrogen bonding
Explanation: Ethanol contains a polar \(O-H\) bond and lone pairs on oxygen. The hydrogen of one ethanol molecule can interact with the oxygen lone pair of another molecule, forming intermolecular hydrogen bonds. These attractions require extra energy to overcome during boiling. Ethane lacks an \(O-H\) bond and cannot form comparable hydrogen-bonded associations.
202. In alcohols, intermolecular hydrogen bonding occurs mainly between:
ⓐ. carbon of one molecule and carbon of another molecule
ⓑ. hydrogen of an alkyl group and carbon of another molecule
ⓒ. \(O-H\) hydrogen and oxygen lone pair of another molecule
ⓓ. oxygen of one molecule and oxygen nucleus of the same molecule only
Correct Answer: \(O-H\) hydrogen and oxygen lone pair of another molecule
Explanation: Alcohol molecules contain a strongly polar \(O-H\) bond. The hydrogen attached to oxygen carries partial positive character and can interact with a lone pair on oxygen of a neighbouring molecule. This attraction is called intermolecular hydrogen bonding. It is not simply a contact between two carbon atoms or between ordinary \(C-H\) hydrogens.
203. Which compound can form intermolecular hydrogen bonds with molecules of the same compound most effectively?
ⓐ. \(CH_3OCH_3\)
ⓑ. \(CH_3CH_2Cl\)
ⓒ. \(CH_3CH_2CH_3\)
ⓓ. \(CH_3CH_2OH\)
Correct Answer: \(CH_3CH_2OH\)
Explanation: \(CH_3CH_2OH\) has an \(O-H\) bond and oxygen lone pairs, so one molecule can donate and another can accept a hydrogen bond. \(CH_3OCH_3\) has oxygen lone pairs but no \(O-H\) bond, so it cannot self-associate by hydrogen-bond donation. Propane and chloroethane do not contain the necessary \(O-H\) group. The alcohol structure therefore supports the strongest self-association among the given compounds.
204. Which statement best explains why lower alcohols are generally more soluble in water than comparable hydrocarbons?
ⓐ. Alcohols contain only nonpolar \(C-C\) bonds.
ⓑ. Alcohols have no oxygen atom in their structure.
ⓒ. Alcohols form ionic salts with water instantly.
ⓓ. Alcohols can form hydrogen bonds with water.
Correct Answer: Alcohols can form hydrogen bonds with water.
Explanation: Lower alcohols contain a polar hydroxyl group. The \(O-H\) group of an alcohol can form hydrogen bonds with water molecules. This interaction helps alcohol molecules mix with water more readily than hydrocarbons of comparable size. Hydrocarbons lack such polar groups and are therefore much less soluble in water.
205. Which factor mainly increases the viscosity of alcohols compared with similar hydrocarbons?
ⓐ. Association through hydrogen bonding
ⓑ. Complete absence of molecular attraction
ⓒ. Conversion into metallic crystals
ⓓ. Presence of only nonpolar bonds
Correct Answer: Association through hydrogen bonding
Explanation: Alcohol molecules can attract one another through intermolecular hydrogen bonds. These attractions make the liquid molecules resist flow more than molecules held only by weak dispersion forces. As a result, alcohols often show higher viscosity than comparable hydrocarbons. The effect becomes more noticeable when multiple \(OH\) groups are present.
206. Which compound is expected to have a higher boiling point due to hydrogen bonding?
ⓐ. \(CH_3CH_3\)
ⓑ. \(CH_3OCH_3\)
ⓒ. \(CH_3CH_2OH\)
ⓓ. \(CH_3CH_2CH_3\)
Correct Answer: \(CH_3CH_2OH\)
Explanation: \(CH_3CH_2OH\) contains a hydroxyl group and can form intermolecular hydrogen bonds. \(CH_3OCH_3\) is an ether and cannot donate hydrogen bonds to another molecule of itself because it lacks an \(O-H\) bond. Alkanes such as \(CH_3CH_3\) and \(CH_3CH_2CH_3\) have only weak intermolecular forces. Stronger association in ethanol raises its boiling point.
207. Which statement correctly compares alcohols and haloalkanes of similar molecular mass?
ⓐ. Haloalkanes always boil higher because they contain halogen atoms.
ⓑ. Alcohols often boil higher due to hydrogen bonding.
ⓒ. Both have identical boiling points because both contain carbon.
ⓓ. Alcohols always boil lower because \(O-H\) bonds are nonpolar.
Correct Answer: Alcohols often boil higher due to hydrogen bonding.
Explanation: Alcohols contain an \(O-H\) group, which allows intermolecular hydrogen bonding. Haloalkanes may have polar \(C-X\) bonds, but they do not usually form the same strong self-association through \(O-H\) hydrogen bonds. Therefore alcohols of comparable molecular mass often show higher boiling points. The difference comes from intermolecular attraction, not just the presence of carbon or a heteroatom.
208. Which property of lower alcohols is most directly related to their ability to hydrogen bond with water?
ⓐ. Complete insolubility in water
ⓑ. Absence of polarity
ⓒ. Metallic conductivity
ⓓ. High water miscibility
Correct Answer: High water miscibility
Explanation: Lower alcohols have small hydrocarbon parts and polar hydroxyl groups. Their \(OH\) groups can form hydrogen bonds with water molecules. Because the nonpolar alkyl part is still small, the hydrogen-bonding effect dominates. This explains why alcohols such as methanol and ethanol mix very well with water.
209. Which statement about phenol and hydrogen bonding is accurate?
ⓐ. Phenol cannot form hydrogen bonds because it has no oxygen.
ⓑ. Phenol forms hydrogen bonds only through carbon-carbon bonds.
ⓒ. Phenol forms hydrogen bonds through its \(OH\) group.
ⓓ. Phenol is completely nonpolar because it has an aromatic ring.
Correct Answer: Phenol forms hydrogen bonds through its \(OH\) group.
Explanation: Phenol contains an \(O-H\) group directly attached to an aromatic ring. The hydrogen attached to oxygen can participate in hydrogen bonding with oxygen atoms of other phenol molecules. This contributes to its boiling point being higher than that of many non-hydrogen-bonding aromatic compounds. The aromatic ring affects solubility but does not remove the ability of the \(OH\) group to hydrogen bond.
210. Why is phenol less soluble in water than lower alcohols such as ethanol?
ⓐ. Its aromatic ring reduces the polar \(OH\) effect.
ⓑ. It contains no hydroxyl group.
ⓒ. Its aliphatic ring reduces the polar \(OH\) effect.
ⓓ. It lacks any polar bond in the molecule.
Correct Answer: Its aromatic ring reduces the polar \(OH\) effect.
Explanation: Phenol has a polar \(OH\) group that can form hydrogen bonds with water. However, it also contains a large hydrophobic benzene ring. The nonpolar aromatic portion reduces the overall tendency of phenol to dissolve in water. Lower alcohols such as ethanol have much smaller hydrocarbon parts, so their \(OH\)-water hydrogen bonding has a stronger solubility effect.
211. Which compound contains an \(OH\) group but is less water-soluble than ethanol mainly because of a larger hydrophobic part?
ⓐ. \(CH_3OH\)
ⓑ. \(CH_3CH_2OH\)
ⓒ. \(CH_3OCH_3\)
ⓓ. \(C_6H_5OH\)
Correct Answer: \(C_6H_5OH\)
Explanation: \(C_6H_5OH\), phenol, contains a hydroxyl group capable of hydrogen bonding with water. Its benzene ring is large and hydrophobic compared with the alkyl group in ethanol. This reduces its solubility in water. The compound still shows hydrogen bonding, but the aromatic ring limits complete miscibility.
212. Which comparison between phenol and benzene is most reasonable?
ⓐ. Benzene has stronger hydrogen bonding than phenol.
ⓑ. Phenol boils higher because it hydrogen-bonds.
ⓒ. Both have identical boiling points because both are aromatic.
ⓓ. Phenol is less polar because it contains an \(OH\) group.
Correct Answer: Phenol boils higher because it hydrogen-bonds.
Explanation: Phenol contains an \(O-H\) group and can form intermolecular hydrogen bonds. Benzene has no \(O-H\) bond and is held mainly by weaker intermolecular forces. Because hydrogen bonds require more energy to break, phenol has a higher boiling point than benzene. Aromaticity alone does not make their physical properties identical.
213. Which statement about ethers is correct regarding self-hydrogen bonding?
ⓐ. Ethers self-associate strongly because they have two \(O-H\) bonds.
ⓑ. Ethers self-associate like alcohols because all oxygen compounds donate hydrogen bonds.
ⓒ. Ethers do not self-associate by \(O-H\) hydrogen bonding because they lack an \(O-H\) bond.
ⓓ. Ethers form hydrogen bonds only after losing an alkyl group in water.
Correct Answer: Ethers do not self-associate by \(O-H\) hydrogen bonding because they lack an \(O-H\) bond.
Explanation: Ethers contain oxygen bonded to two carbon groups, as in \(R-O-R'\). They have lone pairs on oxygen but no hydrogen attached to oxygen. Without an \(O-H\) bond, an ether molecule cannot donate a hydrogen bond to another ether molecule in the same way alcohols do. This is why ethers generally have lower boiling points than isomeric alcohols.
214. Which compound can act as a hydrogen-bond acceptor but not as a hydrogen-bond donor through \(O-H\)?
ⓐ. \(CH_3OCH_3\)
ⓑ. \(CH_3CH_2OH\)
ⓒ. \(C_6H_5OH\)
ⓓ. \(HOCH_2CH_2OH\)
Correct Answer: \(CH_3OCH_3\)
Explanation: \(CH_3OCH_3\) is an ether, so its oxygen atom has lone pairs that can accept hydrogen bonds. However, it has no \(O-H\) bond and cannot donate a hydrogen bond through oxygen-bound hydrogen. Alcohols and phenols contain \(O-H\) groups and can act as hydrogen-bond donors. This acceptor-only behaviour is a key feature of ethers.
215. Which compound is expected to have the lower boiling point when compared with its isomeric alcohol \(CH_3CH_2OH\)?
ⓐ. \(CH_3CH_2CH_3\)
ⓑ. \(C_6H_5OH\)
ⓒ. \(HOCH_2CH_2OH\)
ⓓ. \(CH_3OCH_3\)
Correct Answer: \(CH_3OCH_3\)
Explanation: \(CH_3OCH_3\) and \(CH_3CH_2OH\) have the same molecular formula \(C_2H_6O\), but different functional groups. Ethanol contains an \(O-H\) bond and forms intermolecular hydrogen bonds. Dimethyl ether lacks an \(O-H\) bond, so its molecules are less strongly associated. Hence dimethyl ether has a lower boiling point than ethanol.
216. Which statement explains why ethers show some solubility in water despite lacking an \(O-H\) bond?
ⓐ. Their carbon chains are completely ionic in water.
ⓑ. Oxygen lone pairs accept hydrogen bonds from water.
ⓒ. They form \(O-H\) bonds by breaking all \(C-O\) bonds first.
ⓓ. They are always converted into alcohols in cold water.
Correct Answer: Oxygen lone pairs accept hydrogen bonds from water.
Explanation: Ether oxygen has lone pairs and can accept hydrogen bonds from water molecules. This gives lower ethers some solubility in water. However, ethers cannot donate hydrogen bonds because they do not contain an \(O-H\) bond. As the hydrocarbon part becomes larger, the nonpolar effect reduces solubility.
217. Which order best represents the ability for self-association through \(O-H\) hydrogen bonding?
ⓐ. Alcohols and phenols \(>\) ethers
ⓑ. Ethers \(>\) alcohols and phenols
ⓒ. Hydrocarbons \(>\) alcohols
ⓓ. Ethers \(=\) alkanes \(>\) phenols
Correct Answer: Alcohols and phenols \(>\) ethers
Explanation: Alcohols and phenols contain an \(O-H\) bond and oxygen lone pairs, allowing molecules of the same compound to form hydrogen-bonded associations. Ethers have oxygen lone pairs but do not have an \(O-H\) bond. Therefore ethers cannot self-associate through \(O-H\) hydrogen bonding in the same way. This difference strongly affects boiling point trends.
218. Which statement best compares ethanol and dimethyl ether in water?
ⓐ. Dimethyl ether donates and accepts H-bonds; ethanol mainly accepts.
ⓑ. Ethanol cannot form hydrogen bonds with water.
ⓒ. Ethanol donates and accepts H-bonds; dimethyl ether mainly accepts.
ⓓ. Both are completely nonpolar and insoluble in water.
Correct Answer: Ethanol donates and accepts H-bonds; dimethyl ether mainly accepts.
Explanation: Ethanol has an \(O-H\) bond, so it can donate a hydrogen bond, and its oxygen lone pairs can accept hydrogen bonds. Dimethyl ether has oxygen lone pairs, so it can accept hydrogen bonds from water. It cannot donate through \(O-H\) because that bond is absent. This explains why ethanol interacts more strongly with water than dimethyl ether.
219. Why do lower ethers generally boil below isomeric alcohols?
ⓐ. Ethers have stronger \(O-H\) hydrogen bonding.
ⓑ. Ethers contain no polar bonds at all.
ⓒ. Alcohols have no intermolecular attraction.
ⓓ. Ethers lack self \(O-H\) hydrogen bonding.
Correct Answer: Ethers lack self \(O-H\) hydrogen bonding.
Explanation: Isomeric alcohols and ethers may have the same molecular formula, but their functional groups differ. Alcohols contain \(O-H\) bonds and can form strong intermolecular hydrogen bonds. Ethers lack \(O-H\) bonds and cannot self-associate in the same way. As a result, ethers usually require less energy to boil than their isomeric alcohols.
220. Which statement correctly describes hydrogen bonding in \(C_2H_5OC_2H_5\)?
ⓐ. It donates hydrogen bonds through oxygen-bound hydrogen.
ⓑ. It accepts hydrogen bonds but cannot donate through \(O-H\).
ⓒ. It self-associates strongly like ethane-\(1,2\)-diol.
ⓓ. It has no oxygen lone pairs available for interaction.
Correct Answer: It accepts hydrogen bonds but cannot donate through \(O-H\).
Explanation: \(C_2H_5OC_2H_5\) is diethyl ether. Its oxygen atom has lone pairs, so it can accept hydrogen bonds from suitable donors such as water. However, it does not contain an \(O-H\) bond, so it cannot donate hydrogen bonds through oxygen-bound hydrogen. This distinction explains its lower boiling point compared with alcohols of comparable molar mass.
