Online Test — Aldehydes, Ketones and Carboxylic Acids
20 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 20
The hybridisation of the carbonyl carbon in an aldehyde is:
sp2
sp
sp3
sp3d
Explanation: Three coplanar sigma bonds and one pi bond mean sp2.
Question 2 of 20
Rosenmund reduction converts an acyl chloride into a(n):
alcohol
aldehyde
alkane
ester
Explanation: H2 over Pd/BaSO4 stops at the aldehyde.
Question 3 of 20
Which compound gives a positive iodoform test?
diethyl ketone
propanal
acetone
benzaldehyde
Explanation: Acetone has a CH3CO– group, so it gives CHI3.
Question 4 of 20
Tollens reagent is:
Fehling solution
Schiff reagent
I2/NaOH
ammoniacal AgNO3
Explanation: Tollens reagent is ammoniacal silver nitrate; aldehydes give a silver mirror.
Question 5 of 20
The strongest acid among the following is:
trichloroacetic acid
formic acid
chloroacetic acid
acetic acid
Explanation: Three –I chlorine atoms stabilise the anion most, so trichloroacetic acid is strongest.
Question 6 of 20
Which aldehyde undergoes the Cannizzaro reaction?
acetaldehyde
benzaldehyde
butanal
propanal
Explanation: Benzaldehyde has no α-H and disproportionates in conc. alkali.
Question 7 of 20
Clemmensen reduction uses:
NH2NH2/KOH
NaBH4
Zn-Hg/conc. HCl
LiAlH4
Explanation: Clemmensen uses zinc amalgam with concentrated HCl (acidic conditions).
Question 8 of 20
Addition of NaHSO3 to acetaldehyde gives a:
cyanohydrin
hemiacetal
hydrazone
crystalline bisulphite adduct
Explanation: The bisulphite addition product is crystalline and used for purification.
Question 9 of 20
Aldehydes are more reactive than ketones in nucleophilic addition because of:
lower steric hindrance and higher δ+
greater steric hindrance
hydrogen bonding
higher molar mass
Explanation: Less crowding and a more electrophilic carbon make aldehydes more reactive.
Question 10 of 20
Grignard reagent + dry ice (CO2) then H3O+ yields a:
ketone
carboxylic acid
primary alcohol
aldehyde
Explanation: RMgX adds to CO2 to give RCOOH after hydrolysis.
Question 11 of 20
Which reagent oxidises a primary alcohol only up to the aldehyde?
K2Cr2O7/H+
acidified KMnO4
PCC
hot conc. HNO3
Explanation: PCC is mild and anhydrous, stopping at the aldehyde.
Question 12 of 20
The product of aldol condensation of acetaldehyde after dehydration is:
butanal
butanoic acid
butan-2-one
but-2-enal
Explanation: 3-Hydroxybutanal loses water to give but-2-enal.
Question 13 of 20
Reaction of acetic acid with SOCl2 gives:
acetyl chloride
acetamide
ethyl acetate
acetic anhydride
Explanation: SOCl2 converts –COOH to –COCl (acetyl chloride).
Question 14 of 20
Which test distinguishes an aliphatic aldehyde from an aromatic aldehyde?
Tollens
Fehling
2,4-DNP
iodoform
Explanation: Fehling is positive only for aliphatic aldehydes; aromatic ones do not respond.
Question 15 of 20
The carboxyl group on a benzene ring is:
activating, o/p-directing
activating, meta-directing
deactivating, meta-directing
deactivating, o/p-directing
Explanation: –COOH withdraws electrons, deactivating the ring and directing meta.
Question 16 of 20
Which compound will NOT respond to Tollens test?
benzaldehyde
methanal
ethanal
propanone
Explanation: Propanone is a ketone and does not reduce Tollens reagent.
Question 17 of 20
Wolff–Kishner reduction of cyclohexanone gives:
cyclohexane
cyclohexanol
cyclohexene
benzene
Explanation: NH2NH2/KOH reduces C=O fully to CH2, giving cyclohexane.
Question 18 of 20
Which has the lowest $pK_a$ (strongest acid)?
CH3COOH
HCOOH
CH3CH2COOH
C6H5OH
Explanation: Formic acid (no electron-donating alkyl group) is the strongest of these and has the lowest $pK_a$; phenol is much weaker.
Question 19 of 20
Acetals are formed by addition of which nucleophile to a carbonyl?
HCN
NH3
alcohol (with dry HCl)
NaHSO3
Explanation: Two equivalents of alcohol with dry HCl give an acetal (a protecting group).
Question 20 of 20
A 2,4-dinitrophenylhydrazine (2,4-DNP) test is used to detect:
carboxylic acids
alcohols
ethers
the carbonyl group
Explanation: 2,4-DNP gives an orange precipitate with aldehydes and ketones (the >C=O group).