Aldehydes Ketones and Carboxylic Acids Practice Quiz (32 questions)

1. Which structural feature defines a carbonyl group?

A. A carbon–oxygen double bond

B. A carbon–carbon double bond

C. An oxygen–hydrogen double bond

D. A carbon–oxygen single bond

Answer: (A)

Explanation

A carbonyl group consists of carbon double-bonded to oxygen. A single C–O bond is not a carbonyl, a C=C bond lacks oxygen, and an O–H double bond is not the defined group.

2. A compound has a carbonyl carbon bonded to one carbon atom and one hydrogen atom. How is the compound classified?

A. A ketone

B. An alcohol

C. A carboxylic acid

D. An aldehyde

Answer: (D)

Explanation

An aldehyde has a carbonyl carbon bonded to a carbon and a hydrogen. A ketone has two carbon attachments, while a carboxylic acid and an alcohol are distinguished by hydroxyl-containing groups.

3. In a polar carbonyl group, which behavior is expected when a nucleophile approaches?

A. The nucleophile is attracted to the electrophilic carbonyl carbon

B. The nucleophile is attracted equally to both atoms of a nonpolar bond

C. The nucleophile is repelled by the electrophilic carbonyl carbon

D. The nucleophile is attracted to the electrophilic oxygen atom

Answer: (A)

Explanation

Oxygen is more electronegative than carbon, polarizing the bond so the carbonyl carbon is electrophilic and the oxygen nucleophilic. Reversing the polarity or treating the bond as nonpolar gives the wrong site of attraction.

4. An open-chain aliphatic ketone is derived from the corresponding alkane named hexane. Which ending is used in its IUPAC name?

A. -oic acid

B. -one

C. -ane

D. -al

Answer: (B)

Explanation

Open-chain aliphatic ketones are named from the corresponding alkane by replacing the final -e with -one. The -al ending is used for aldehydes, -ane retains the alkane name, and -oic acid names carboxylic acids.

5. A five-carbon aldehyde chain is being numbered for naming, with the aldehyde group at one end. From which end should numbering begin?

A. From the aldehyde-carbon end

B. From the end farthest from the aldehyde group

C. From the end nearest the first substituent

D. From the end nearest the chain midpoint

Answer: (A)

Explanation

Aldehyde chains are numbered starting at the aldehyde carbon, which is the end bearing the group. Numbering from a carbonyl-nearest end is the ketone rule, while the other choices ignore the aldehyde group's required starting point.

6. A chemist oxidizes one sample of 1-propanol and another of 2-propanol. Which pair of carbonyl products should form, respectively?

A. Propanal and propanal

B. Propanone and propanal

C. Propanone and propanone

D. Propanal and propanone

Answer: (D)

Explanation

Primary alcohols oxidize to aldehydes, while secondary alcohols oxidize to ketones. Reversing the sequence swaps those products, and assigning the same product to both alcohols ignores the distinction.

7. A chemist needs to convert an acyl chloride to an aldehyde by hydrogenation. Which catalyst and support should be used for this named reaction?

A. Copper on barium sulfate

B. Silver on alumina

C. Palladium on carbon

D. Palladium on barium sulfate

Answer: (D)

Explanation

Rosenmund reduction hydrogenates acyl chlorides to aldehydes using palladium on barium sulfate. Palladium on carbon changes the support, while copper and silver are associated with alcohol dehydrogenation rather than this reduction.

8. A student compares a carbonyl compound with a hydrocarbon, an ether, and an alcohol of comparable molecular mass. Which boiling-point pattern should the student expect?

A. Above the alcohol, but below the hydrocarbon and ether

B. Below the hydrocarbon and ether, but above the alcohol

C. Above the hydrocarbon and ether, but below the alcohol

D. Below the hydrocarbon, but above the ether and alcohol

Answer: (C)

Explanation

Dipole–dipole association raises carbonyl compounds’ boiling points above those of comparable hydrocarbons and ethers, while the absence of intermolecular hydrogen bonding keeps them below comparable alcohols. The hydrogen-bonding misconception places them above alcohols, and treating them as nonpolar misses their dipole-based association.

9. Two aldehydes have the same functional group, but one has a substantially longer alkyl chain. What change in water solubility is expected for the longer-chain aldehyde?

A. Its water solubility is lower

B. Its water solubility is higher

C. Its water solubility is unchanged

D. It becomes miscible in all proportions

Answer: (A)

Explanation

Water solubility decreases rapidly as the alkyl chain grows, even though the carbonyl group can hydrogen-bond with water. Equal solubility ignores the chain-length effect, while miscibility in all proportions applies to lower members.

10. During a reaction, a nucleophile attacks a carbonyl group. Which sequence of events produces the neutral addition product?

A. Attack at carbonyl carbon, tetrahedral alkoxide formation, then protonation

B. Attack at carbonyl carbon, unchanged planar intermediate, then protonation

C. Protonation of carbonyl oxygen, then attack at carbonyl carbon

D. Attack at carbonyl oxygen, tetrahedral alcohol formation, then deprotonation

Answer: (A)

Explanation

Nucleophilic attack at the electrophilic carbonyl carbon changes carbon from sp2 to sp3 and forms a tetrahedral alkoxide, which is then protonated. Attacking oxygen misidentifies the target, retaining a planar intermediate misses the hybridisation change, and prior protonation reverses the described sequence.

11. A chemist compares an aldehyde and a ketone with the same nucleophile. Which feature generally makes the aldehyde react faster in nucleophilic addition?

A. It has more steric hindrance and a less electrophilic carbonyl carbon

B. It is more readily oxidised, which accelerates nucleophilic addition

C. It has less steric hindrance but a less electrophilic carbonyl carbon

D. It has less steric hindrance and a more electrophilic carbonyl carbon

Answer: (D)

Explanation

A ketone’s two alkyl groups both hinder nucleophile approach and reduce carbonyl-carbon electrophilicity more strongly, so aldehydes are generally more reactive. The claim that alkyl groups increase electrophilicity reverses their electronic effect; assigning greater hindrance to aldehydes reverses the steric comparison; oxidation is a different reaction.

12. A chemist reduces propanal with sodium borohydride. What type of alcohol is formed?

A. A carboxylic acid

B. A primary alcohol

C. A hydrocarbon with a CH2 group

D. A secondary alcohol

Answer: (B)

Explanation

Sodium borohydride reduces aldehydes to primary alcohols, while ketones give secondary alcohols. A secondary alcohol applies the ketone pattern, a CH2 product is associated with Clemmensen or Wolff–Kishner reduction, and a carboxylic acid is an oxidation product.

13. A carbonyl compound is treated with hydrazine and then heated with strong alkali. Which transformation does this procedure carry out?

A. Conversion of the carbonyl group to a primary alcohol

B. Conversion of the carbonyl group to a secondary alcohol

C. Conversion of the carbonyl group to a carboxylic acid

D. Conversion of the carbonyl group to CH2

Answer: (D)

Explanation

Wolff–Kishner reduction uses hydrazine followed by heating with strong alkali to convert the carbonyl group to CH2. Zinc amalgam and concentrated hydrochloric acid are Clemmensen conditions; alcohols are products of other reductions, and a carboxylic acid is an oxidation product.

14. A sample of an aldehyde and a sample of a ketone are each treated with a common oxidising agent under mild conditions. Which outcome is generally expected?

A. Both compounds form alcohols through reduction of the carbonyl group

B. The aldehyde forms a carboxylic acid, while the ketone generally resists mild oxidation

C. The ketone forms smaller carboxylic acids through mild bond cleavage

D. The ketone forms a carboxylic acid, while the aldehyde generally resists mild oxidation

Answer: (B)

Explanation

Aldehydes are readily oxidised to carboxylic acids by common oxidants, whereas ketones generally need vigorous conditions that cleave carbon–carbon bonds. The reverse reactivity claim swaps their oxidation behaviour, alcohol formation is reduction, and mild conditions do not describe the vigorous ketone oxidation process.

15. Why can an aldehyde or ketone lose an alpha hydrogen relatively readily?

A. The carbonyl withdraws electrons, and the conjugate base is resonance-stabilized.

B. The oxygen atom alone makes the alpha hydrogen acidic, independent of the carbonyl group.

C. The carbonyl withdraws electrons, but the conjugate base lacks resonance stabilization.

D. The carbonyl donates electrons, and the conjugate base is resonance-stabilized.

Answer: (A)

Explanation

The electron-withdrawing carbonyl group and resonance stabilization of the conjugate base together explain alpha-hydrogen acidity. Electron donation reverses the carbonyl effect, while the other distractors omit or misplace the stated stabilization.

16. A ketone with at least one alpha hydrogen is treated with dilute base. What product sequence is expected?

A. A beta-hydroxy ketone forms, then may lose water to yield an alpha,beta-unsaturated carbonyl.

B. An alcohol and a carboxylate form by disproportionation, without a beta-hydroxy intermediate.

C. A carboxylate forms directly, with no carbon-carbon bond-forming step.

D. An alpha,beta-unsaturated carbonyl forms first, then gains water to yield a beta-hydroxy ketone.

Answer: (A)

Explanation

A carbonyl compound with an alpha hydrogen undergoes base-catalysed aldol addition to form a beta-hydroxy carbonyl, which can dehydrate to an alpha,beta-unsaturated carbonyl. Disproportionation is the Cannizzaro pathway, and the dehydration distractor reverses the sequence.

17. An aldehyde with no alpha hydrogen is heated with concentrated alkali. What transformation characterizes the reaction?

A. Both aldehyde molecules are oxidised to carboxylates without reduction.

B. Two aldehyde molecules combine into a beta-hydroxy carbonyl through aldol addition.

C. Both aldehyde molecules are reduced to alcohols without oxidation.

D. One aldehyde molecule is reduced to an alcohol while another is oxidised to a carboxylate.

Answer: (D)

Explanation

The Cannizzaro reaction is disproportionation: one aldehyde molecule is reduced to an alcohol and another is oxidised to a carboxylate. Aldol addition requires an alpha hydrogen, while the other alternatives omit one side of the redox process.

18. A laboratory needs a formaldehyde-based solution to preserve biological specimens and a resin for making polymeric products. Which material fits both uses?

A. Benzaldehyde as an aromatic industrial material

B. Acetaldehyde as a chemical manufacturing feedstock

C. Formaldehyde as a 40% formalin solution

D. Acetone as a common industrial solvent

Answer: (C)

Explanation

Formaldehyde in 40% formalin is used to preserve biological specimens, and formaldehyde is also used to make Bakelite and urea-formaldehyde glues. Benzaldehyde is associated with perfumery and dyes, acetaldehyde with chemical manufacture, and acetone with solvent use.

19. A manufacturer needs a ketone commonly used as an industrial solvent. Which pair consists of such solvents?

A. Benzaldehyde and acetone

B. Acetaldehyde and ethyl methyl ketone

C. Acetone and ethyl methyl ketone

D. Formaldehyde and benzaldehyde

Answer: (C)

Explanation

Acetone and ethyl methyl ketone are common industrial solvents. Benzaldehyde is used in perfumery and dye industries, acetaldehyde serves as a manufacturing starting material, and formaldehyde is used in preservation and polymer production.

20. An unbranched saturated acid has four carbon atoms in its longest chain, including the carboxyl carbon. What is its IUPAC name?

A. Butane acid

B. Butanoic acid

C. Propanoic acid

D. Butyric acid

Answer: (B)

Explanation

The corresponding four-carbon alkane is butane; replacing its final -e with -oic acid gives butanoic acid, with the carboxyl carbon numbered one. Butyric acid is the common name, propanoic acid has one fewer carbon, and butane acid does not follow the naming rule.

21. A compound has a –COOH group attached to an aromatic group. How is it classified based on the group attached to the carboxyl carbon?

A. An aromatic ester

B. An aromatic carboxylic acid

C. An aliphatic carboxylic acid

D. An aliphatic aldehyde

Answer: (B)

Explanation

Carboxylic acids contain the –COOH group and are classified as aromatic when an aryl group is attached to the carboxyl carbon. An alkyl attachment makes the acid aliphatic, while an ester and an aldehyde have different functional groups.

22. A chemist reacts an ethyl Grignard reagent with carbon dioxide and then acidifies the product. Which carboxylic acid is formed?

A. Butanoic acid

B. Ethanoic acid

C. Propanoic acid

D. Propene

Answer: (C)

Explanation

Reaction with carbon dioxide followed by acidification adds one carbon to the alkyl group, so the two-carbon ethyl group gives the three-carbon acid propanoic acid. Ethanoic acid omits the added carbon, while butanoic acid adds an extra carbon.

23. A laboratory oxidation is performed on a primary alcohol using a suitable oxidising agent. What product class is expected?

A. An aldehyde

B. A primary alcohol

C. A carboxylic acid

D. A ketone

Answer: (C)

Explanation

Suitable oxidising agents convert primary alcohols to carboxylic acids. An aldehyde is an intermediate in some oxidation pathways, while reduction produces alcohols and ketones are not the stated product of primary-alcohol oxidation.

24. Why do carboxylic acids have higher boiling points than aldehydes, ketones, and alcohols of comparable molecular mass?

A. Their molecules form stronger covalent bonds within each molecule.

B. Their intermolecular forces are weaker, so more energy is needed to boil them.

C. Their lower molecular masses require more energy to separate their molecules.

D. Extensive intermolecular hydrogen bonding promotes dimer formation.

Answer: (D)

Explanation

Intermolecular hydrogen bonding leads to extensive association and dimer formation, raising the energy needed to boil carboxylic acids. The covalent-bond explanation confuses intermolecular association with bonds within a molecule, while weaker forces and lower molecular mass do not explain the higher boiling points.

25. A chemist compares two aliphatic carboxylic acids, one with four carbon atoms and one with eight. What should be expected about their behavior in water?

A. The eight-carbon acid is more soluble because longer chains form more hydrogen bonds.

B. Both acids are practically insoluble because each contains a hydrocarbon chain.

C. The four-carbon acid is miscible, while the eight-carbon acid is less soluble.

D. The four-carbon acid is less soluble because shorter chains are more hydrophobic.

Answer: (C)

Explanation

Carboxylic acids with up to four carbon atoms are miscible with water, and solubility decreases as the hydrocarbon chain grows. Equal solubility ignores this trend, while the other alternatives reverse the chain-length effect or confuse solubility with physical state.

26. Two acids have pKa values of 3.2 and 5.1. Which conclusion follows from the pKa definition?

A. The acids have equal strength because both pKa values are positive.

B. The acid with pKa 5.1 is stronger.

C. The acid with pKa 3.2 is weaker because its dissociation constant is smaller.

D. The acid with pKa 3.2 is stronger.

Answer: (D)

Explanation

Because $\mathrm{p}K_a=-\log K_a$, a smaller pKa corresponds to a larger acid dissociation constant and a stronger acid. The larger-pKa choice reverses the relationship, and pKa is neither directly proportional to $K_a$ nor a measure of undissociated-acid concentration.

27. A comparison shows that a carboxylic acid is stronger than a simple phenol. Which explanation best accounts for this difference?

A. Carboxylate charge is concentrated on one oxygen, making the conjugate base less stable.

B. Hydrogen bonding between neutral acid molecules directly accounts for the acidity difference.

C. Carboxylate charge is delocalized over two oxygen atoms in equivalent resonance structures.

D. Phenoxide charge is delocalized equally over two oxygen atoms in equivalent resonance structures.

Answer: (C)

Explanation

The carboxylate conjugate base is stabilized by two equivalent resonance structures that delocalize negative charge over two oxygen atoms, favoring proton loss. The phenoxide option misassigns its resonance distribution, and the alternatives either deny carboxylate stabilization or invoke a physical property rather than conjugate-base stability.

28. Two otherwise similar carboxylic acids differ by a substituent: one has an electron-withdrawing group and the other an electron-donating group. Which prediction follows?

A. The electron-withdrawing substituent weakens the acid by destabilizing its conjugate base.

B. The two substituents have the same effect because conjugate-base stability is unchanged.

C. The electron-withdrawing substituent strengthens the acid by stabilizing its conjugate base.

D. The electron-donating substituent strengthens the acid by stabilizing its conjugate base.

Answer: (C)

Explanation

Electron-withdrawing substituents stabilize the carboxylate conjugate base and increase acid strength, while electron-donating substituents destabilize it and decrease strength. The electron-donating choice reverses the substituent effects; the remaining choices disregard or invert the role of conjugate-base stability.

29. A chemist adds sodium hydrogencarbonate to an unknown organic sample and observes effervescence of carbon dioxide. Which functional group does this result help identify?

A. An alcohol group

B. A carboxyl group

C. An aldehyde group

D. An ester group

Answer: (B)

Explanation

Carboxylic acids release carbon dioxide when they react with carbonates or hydrogencarbonates, making this a test for the carboxyl group. Hydrogen release is associated with electropositive metals, while ester formation requires an alcohol or phenol.

30. A laboratory prepares an ester by reacting a carboxylic acid with a phenol in the presence of a mineral acid catalyst. Which description best matches the reaction mechanism and by-product?

A. Electrophilic substitution with loss of hydrogen

B. Salt formation with loss of a mineral acid

C. Nucleophilic addition with loss of carbon dioxide

D. Nucleophilic acyl substitution with loss of water

Answer: (D)

Explanation

Esterification proceeds through nucleophilic acyl substitution, and water is eliminated after the intermediate is formed. Carbon dioxide loss is associated with decarboxylation or reactions involving carbonates, not esterification.

31. A food producer needs a carboxylic acid commonly used both as a solvent and as vinegar. Which acid fits this use?

A. Ethanoic acid

B. Hexanedioic acid

C. Benzoic acid

D. Methanoic acid

Answer: (A)

Explanation

Ethanoic acid is used as a solvent and as vinegar in the food industry. Methanoic acid is associated with several industrial applications, while hexanedioic acid is used to manufacture nylon-6,6.

32. A manufacturer is selecting a carboxylic acid feedstock for producing nylon-6,6. Which acid should be chosen?

A. Higher fatty acids

B. Ethanoic acid

C. Benzoic acid

D. Hexanedioic acid

Answer: (D)

Explanation

Hexanedioic acid is used to manufacture nylon-6,6. Ethanoic acid is used as a solvent and vinegar, benzoic acid esters are used in perfumery, and higher fatty acids are used to manufacture soaps and detergents.